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8-Concurrency.html
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<!DOCTYPE html><html lang="en-US"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width,height=device-height,initial-scale=1.0"><meta name="apple-mobile-web-app-capable" content="yes"><meta http-equiv="X-UA-Compatible" content="ie=edge"><meta property="og:type" content="website"><meta name="twitter:card" content="summary"><style>@media screen{body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button{appearance:none;background-color:initial;border:0;color:inherit;cursor:pointer;font-size:inherit;opacity:.8;outline:none;padding:0;transition:opacity .2s linear;-webkit-tap-highlight-color:transparent}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:disabled,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button:disabled,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button:disabled,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button:disabled{cursor:not-allowed;opacity:.15!important}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:hover,body[data-bespoke-view=next] .bespoke-marp-parent>.bespoke-marp-osc>button:hover,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-info-container button:hover,body[data-bespoke-view=presenter] .bespoke-marp-presenter-container .bespoke-marp-presenter-note-container button:hover{opacity:1}body[data-bespoke-view=""] .bespoke-marp-parent>.bespoke-marp-osc>button:hover:active,body[data-bespoke-view=next] 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:is(h1, marp-h1){font-size:2em;margin:0.67em 0}div#\:\$p > svg > foreignObject > section video::-webkit-media-controls{will-change:transform}@page {size:1280px 720px;margin:0}@media print{html, body{background-color:#fff;margin:0;page-break-inside:avoid;break-inside:avoid-page}div#\:\$p > svg > foreignObject > section{page-break-before:always;break-before:page}div#\:\$p > svg > foreignObject > section, div#\:\$p > svg > foreignObject > section *{-webkit-print-color-adjust:exact!important;animation-delay:0s!important;animation-duration:0s!important;color-adjust:exact!important;transition:none!important}div#\:\$p > svg[data-marpit-svg]{display:block;height:100vh;width:100vw}}div#\:\$p > svg > foreignObject > :where(section){container-type:size}div#\:\$p > svg > foreignObject > section img[data-marp-twemoji]{background:transparent;height:1em;margin:0 .05em 0 .1em;vertical-align:-.1em;width:1em}/*!
* Marp / Marpit Gaia theme.
*
* @theme gaia
* @author Yuki Hattori
*
* @auto-scaling true
* @size 16:9 1280px 720px
* @size 4:3 960px 720px
*/div#\:\$p > svg > foreignObject > section :is(pre, marp-pre) code.hljs{display:block;overflow-x:auto;padding:1em}div#\:\$p > svg > foreignObject > section code.hljs{padding:3px 5px}div#\:\$p > svg > foreignObject > section .hljs{background:#000;color:#f8f8f8}div#\:\$p > svg > foreignObject > section .hljs-comment,div#\:\$p > svg > foreignObject > section .hljs-quote{color:#aeaeae;font-style:italic}div#\:\$p > svg > foreignObject > section .hljs-keyword,div#\:\$p > svg > foreignObject > section .hljs-selector-tag,div#\:\$p > svg > foreignObject > section .hljs-type{color:#e28964}div#\:\$p > svg > foreignObject > section .hljs-string{color:#65b042}div#\:\$p > svg > foreignObject > section .hljs-subst{color:#daefa3}div#\:\$p > svg > foreignObject > section .hljs-link,div#\:\$p > svg > foreignObject > section .hljs-regexp{color:#e9c062}div#\:\$p > svg > foreignObject > section .hljs-name,div#\:\$p > svg > foreignObject > section .hljs-section,div#\:\$p > svg > foreignObject > section 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marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{font-weight:inherit}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h2, marp-h2)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h3, marp-h3)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h4, marp-h4)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h5, marp-h5)::part(auto-scaling),div#\:\$p > svg > foreignObject > section :is(h6, marp-h6)::part(auto-scaling){max-height:580px}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1){font-size:1.8em}div#\:\$p > svg > foreignObject > section :is(h2, marp-h2){font-size:1.5em}div#\:\$p > svg > foreignObject > section :is(h3, marp-h3){font-size:1.3em}div#\:\$p > svg > foreignObject > section :is(h4, 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:is(pre, marp-pre)::part(auto-scaling){max-height:calc(580px - 1em)}div#\:\$p > svg > foreignObject > section blockquote{margin:1em 0 0;padding:0 1em;position:relative}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before{content:"“";display:block;font-family:Times New Roman,serif;font-weight:700;position:absolute}div#\:\$p > svg > foreignObject > section blockquote:before{left:0;top:0}div#\:\$p > svg > foreignObject > section blockquote:after{bottom:0;right:0;transform:rotate(180deg)}div#\:\$p > svg > foreignObject > section blockquote>:first-child{margin-top:0}div#\:\$p > svg > foreignObject > section mark{background:transparent}div#\:\$p > svg > foreignObject > section table{border-collapse:collapse;border-spacing:0;margin:1em 0 0}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-style:solid;border-width:1px;padding:.2em .4em}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section:after{box-sizing:border-box;font-size:66%;height:70px;line-height:50px;overflow:hidden;padding:10px 25px;position:absolute}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:66%;}div#\:\$p > svg > foreignObject > section header{top:0}div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header{left:0;right:0}div#\:\$p > svg > foreignObject > section footer{bottom:0}div#\:\$p > svg > foreignObject > section{background-color:var(--color-background);background-image:linear-gradient(135deg, hsla(0,0%,53%,0), hsla(0,0%,53%,.02) 50%, hsla(0,0%,100%,0) 0, hsla(0,0%,100%,.05));color:var(--color-foreground);font-family:Lato,Avenir Next,Avenir,Trebuchet MS,Segoe UI,sans-serif;font-size:35px;height:720px;letter-spacing:1.25px;line-height:1.35;padding:70px;width:1280px;word-wrap:break-word;--color-background:#fff8e1;--color-background-stripe:rgba(69,90,100,.1);--color-foreground:#455a64;--color-dimmed:#6a7a7d;--color-highlight:#0288d1;}div#\:\$p > svg > foreignObject > section{--marpit-root-font-size:35px;}div#\:\$p > svg > foreignObject > section:after{bottom:0;font-size:80%;right:0}div#\:\$p > svg > foreignObject > section:after{--marpit-root-font-size:80%;}div#\:\$p > svg > foreignObject > section a,div#\:\$p > svg > foreignObject > section mark{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section code{background:var(--color-dimmed);color:var(--color-background)}div#\:\$p > svg > foreignObject > section :is(h1, marp-h1) strong,div#\:\$p > svg > foreignObject > section :is(h2, marp-h2) strong,div#\:\$p > svg > foreignObject > section :is(h3, marp-h3) strong,div#\:\$p > svg > foreignObject > section :is(h4, marp-h4) strong,div#\:\$p > svg > foreignObject > section :is(h5, marp-h5) strong,div#\:\$p > svg > foreignObject > section :is(h6, marp-h6) strong{color:var(--color-highlight)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre){background:var(--color-foreground)}div#\:\$p > svg > foreignObject > section :is(pre, marp-pre)>code{background:transparent}div#\:\$p > svg > foreignObject > section blockquote:after,div#\:\$p > svg > foreignObject > section blockquote:before,div#\:\$p > svg > foreignObject > section footer,div#\:\$p > svg > foreignObject > section header,div#\:\$p > svg > foreignObject > section section:after{color:var(--color-dimmed)}div#\:\$p > svg > foreignObject > section table td,div#\:\$p > svg > foreignObject > section table th{border-color:var(--color-foreground)}div#\:\$p > svg > foreignObject > section table thead th{background:var(--color-foreground);color:var(--color-background)}div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) td,div#\:\$p > svg > foreignObject > section table tbody>tr:nth-child(odd) th{background:var(--color-background-stripe, transparent)}div#\:\$p > svg > foreignObject > section>:first-child,div#\:\$p > svg > foreignObject > section>header:first-child+*{margin-top:0}div#\:\$p > svg > foreignObject > section:where(.invert){--color-background:#455a64;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#dad8c8;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.gaia){--color-background:#0288d1;--color-background-stripe:rgba(255,248,225,.1);--color-foreground:#fff8e1;--color-dimmed:#cce2de;--color-highlight:#81d4fa;}div#\:\$p > svg > foreignObject > section:where(.lead){align-items:stretch;flex-flow:column nowrap;place-content:safe center center}div#\:\$p > svg > foreignObject > section:where(.lead) :is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) :is(h6, marp-h6){text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) p{text-align:center}div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h1, marp-h1),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h2, marp-h2),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h3, marp-h3),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h4, marp-h4),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h5, marp-h5),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>:is(h6, marp-h6),div#\:\$p > svg > foreignObject > section:where(.lead) blockquote>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) ol>li>p,div#\:\$p > svg > foreignObject > section:where(.lead) ul>li>p{text-align:left}div#\:\$p > svg > foreignObject > section:where(.lead) table{margin-left:auto;margin-right:auto}div#\:\$p > svg > foreignObject > section img{display:block;margin:0 auto}div#\:\$p > svg > foreignObject > section table{margin-left:auto;margin-right:auto;font-size:25px;width:100%;table-layout:fixed}div#\:\$p > svg > foreignObject > section td{border:1px solid black;text-align:center;padding:10px}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]{columns:initial!important;display:block!important;padding:0!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"]::after, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::before, div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"]::after{display:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container]{all:initial;display:flex;flex-direction:row;height:100%;overflow:hidden;width:100%}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container][data-marpit-advanced-background-direction="vertical"]{flex-direction:column}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split] > div[data-marpit-advanced-background-container]{width:var(--marpit-advanced-background-split, 50%)}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"][data-marpit-advanced-background-split="right"] > div[data-marpit-advanced-background-container]{margin-left:calc(100% - var(--marpit-advanced-background-split, 50%))}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure{all:initial;background-position:center;background-repeat:no-repeat;background-size:cover;flex:auto;margin:0}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="background"] > div[data-marpit-advanced-background-container] > figure > figcaption{position:absolute;border:0;clip:rect(0, 0, 0, 0);height:1px;margin:-1px;overflow:hidden;padding:0;white-space:nowrap;width:1px}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="content"], div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"]{background:transparent!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background="pseudo"], div#\:\$p > svg[data-marpit-svg] > foreignObject[data-marpit-advanced-background="pseudo"]{pointer-events:none!important}div#\:\$p > svg > foreignObject > section[data-marpit-advanced-background-split]{width:100%;height:100%}
</style></head><body><div class="bespoke-marp-osc"><button data-bespoke-marp-osc="prev" tabindex="-1" title="Previous slide">Previous slide</button><span data-bespoke-marp-osc="page"></span><button data-bespoke-marp-osc="next" tabindex="-1" title="Next slide">Next slide</button><button data-bespoke-marp-osc="fullscreen" tabindex="-1" title="Toggle fullscreen (f)">Toggle fullscreen</button><button data-bespoke-marp-osc="presenter" tabindex="-1" title="Open presenter view (p)">Open presenter view</button></div><div id=":$p"><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="en-US" class="lead" data-marpit-pagination="1" style="--paginate:true;--background-color:#fff;--class:lead;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:40%;" data-marpit-pagination-total="82" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/Java_logo.png");background-size:90%;"></figure></div></section></foreignObject><foreignObject width="60%" height="720"><section id="1" data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="en-US" class="lead" data-marpit-pagination="1" style="--paginate:true;--background-color:#fff;--class:lead;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:40%;" data-marpit-pagination-total="82" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h1 id="java%E9%AB%98%E7%BA%A7%E7%A8%8B%E5%BA%8F%E8%AE%BE%E8%AE%A1">Java高级程序设计</h1>
<h2 id="%E5%B9%B6%E5%8F%91%E7%BC%96%E7%A8%8B">并发编程</h2>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-class="lead" data-theme="gaia" lang="en-US" class="lead" data-marpit-pagination="1" style="" data-marpit-pagination-total="82" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="2" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="2" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E5%B9%B6%E5%8F%91">并发</h2>
<blockquote>
<p>空间是并存事物的次序 (Space is the order of existence of states which are simultaneous)</p>
</blockquote>
<div align="right"> —— Leibniz</div>
<blockquote>
<p>The world is concurrent.</p>
</blockquote>
<div align="right"> —— Joe Armstrong</div>
<blockquote>
<p>Concurrency occurs when two or more execution flows are able to run simultaneously.</p>
</blockquote>
<div align="right"> —— Edsger Wybe Dijkstra </div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="3" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="3" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E8%BF%9B%E7%A8%8B-vs-%E7%BA%BF%E7%A8%8B">进程 vs. 线程</h2>
<ul>
<li>进程：是系统进行资源分配和调度的一个独立单位，也是一个具有独立功能的程序；</li>
<li>线程：线程依托于进程而存在，是CPU调度和分派的基本单位，它是比进程更小的能独立运行的基本单位。线程自己基本上不拥有系统资源，只拥有一点在运行中必不可少的资源(如程序计数器、一组寄存器和栈)，但是它可与同属一个进程的其他的线程共享进程所拥有的全部资源。</li>
</ul>
<p><small>区别在于，进程属于资源分配的单位，而线程则是作业调度的单位；进程拥有自己的地址空间，而多个线程拥有自己的堆栈和局部变量，并共享所依托于进程的资源。</small></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="4" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="4" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E5%B9%B6%E5%8F%91-vs-%E5%B9%B6%E8%A1%8C">并发 vs 并行</h2>
<p><img src="images/8/Parallel_Concurrency.png" alt="" /></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="5" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="5" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="jvm-threads">JVM Threads</h2>
<p><img src="images/8/JVM_Threads.png" alt="" style="width:900px;" /></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="6" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="6" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<p><br /><br /><br /><br /><br />
<br /></p>
<div align="center" style="font-size:60px;">初级篇</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="7" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="7" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="runnable"><code>Runnable</code></h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-meta">@FunctionalInterface</span>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">interface</span> <span class="hljs-title class_">Runnable</span>
</code></pre>
<p>The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The class must define a method of no arguments called <code>run</code>.</p>
<p>Since:<br />
JDK1.0</p>
<p><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html">https://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="8" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="8" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E4%B8%BE%E4%BE%8B">举例</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">LiftOff</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">protected</span> <span class="hljs-type">int</span> <span class="hljs-variable">countDown</span> <span class="hljs-operator">=</span> <span class="hljs-number">10</span>; <span class="hljs-comment">// Default</span>
<span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-type">int</span> <span class="hljs-variable">taskCount</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> <span class="hljs-type">int</span> <span class="hljs-variable">id</span> <span class="hljs-operator">=</span> taskCount++;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">LiftOff</span><span class="hljs-params">(<span class="hljs-type">int</span> countDown)</span> { <span class="hljs-built_in">this</span>.countDown = countDown; }
<span class="hljs-keyword">public</span> String <span class="hljs-title function_">status</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"#"</span> + id + <span class="hljs-string">"("</span> + (countDown > <span class="hljs-number">0</span> ? countDown : <span class="hljs-string">"Liftoff!"</span>) + <span class="hljs-string">"), "</span>;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">while</span> (countDown-- > <span class="hljs-number">0</span>) {
System.out.print(status());
Thread.<span class="hljs-keyword">yield</span>(); <span class="hljs-comment">//后面解释</span>
}
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="9" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="9" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="run-it">Run it</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">MainThread</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">LiftOff</span> <span class="hljs-variable">launch</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">LiftOff</span>(<span class="hljs-number">10</span>);
launch.run(); <span class="hljs-comment">//is it a new thread?</span>
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-bash"><span class="hljs-comment">#0(9), #0(8), #0(7), #0(6), #0(5), #0(4), #0(3), #0(2), #0(1), #0(Liftoff!),</span>
</code></pre>
<p><small><code>Runnable</code>接口仅仅定义“任务”</small></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-type">Runnable</span> <span class="hljs-variable">r</span> <span class="hljs-operator">=</span> () -> { task code };
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="10" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="10" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="thread"><code>Thread</code></h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">Thread</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Object</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span>
</code></pre>
<p>A thread is a thread of execution in a program. The Java Virtual Machine allows an application to have multiple threads of execution running concurrently.</p>
<p>Since:<br />
JDK1.0</p>
<p><a href="https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html">https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html</a></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="11" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="11" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E4%B8%BE%E4%BE%8B-1">举例</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">BasicThreads</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-comment">//把任务装进线程里</span>
<span class="hljs-type">Thread</span> <span class="hljs-variable">t</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Thread</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">LiftOff</span>(<span class="hljs-number">10</span>));
t.start();
System.out.println(<span class="hljs-string">"Waiting for LiftOff"</span>);
}
}
</code></pre>
<p><small><code>Thread</code>对象像是运载火箭，<code>Runnable</code>的实现对象就是一个荷载（payload）</small></p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="12" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="12" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E6%88%96%E8%80%85">或者</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SimpleThread</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Thread</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">countDown</span> <span class="hljs-operator">=</span> <span class="hljs-number">5</span>; <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-type">int</span> <span class="hljs-variable">threadCount</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">SimpleThread</span><span class="hljs-params">()</span> {
<span class="hljs-built_in">super</span>(Integer.toString(++threadCount)); start();
}
<span class="hljs-keyword">public</span> String <span class="hljs-title function_">toString</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">return</span> <span class="hljs-string">"#"</span> + getName() + <span class="hljs-string">"("</span> + countDown + <span class="hljs-string">"), "</span>;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">while</span> (<span class="hljs-literal">true</span>) { System.out.print(<span class="hljs-built_in">this</span>); <span class="hljs-keyword">if</span> (--countDown == <span class="hljs-number">0</span>) <span class="hljs-keyword">return</span>; }
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++) { <span class="hljs-keyword">new</span> <span class="hljs-title class_">SimpleThread</span>(); }
}
}
</code></pre>
</section>
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<h2 id="warning">WARNING</h2>
<ul>
<li>
<p>The <code>run()</code> method should not be called directly by the application. The system calls it.</p>
</li>
<li>
<p>If the <code>run()</code> method is called explicitly by the application then the code is executed sequentially not concurrently.</p>
</li>
</ul>
</section>
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<h2 id="%E5%A4%9A%E7%BA%BF%E7%A8%8B%E8%B5%B0%E8%B5%B7">多线程，走起</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">MoreBasicThreads</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++)
<span class="hljs-keyword">new</span> <span class="hljs-title class_">Thread</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">LiftOff</span>(<span class="hljs-number">10</span>)).start();
System.out.println(<span class="hljs-string">"Waiting for LiftOff"</span>);
}
}
</code></pre>
<p>直接启动多个<font color=red>Thread</font></p>
</section>
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<h1 id="%E6%88%96%E8%80%85%E7%94%A8executorservice%E5%90%AF%E5%8A%A8">或者用<code>ExecutorService</code>启动</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">CachedThreadPool</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++)
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">LiftOff</span>(<span class="hljs-number">10</span>));
exec.shutdown();
}
}
</code></pre>
<p><small>根据需要创建新线程的线程池，如果现有线程没有可用的，则创建一个新线程并添加到池中，如果有被使用完但是还没销毁的线程，就复用该线程</small></p>
<p><small><a href="https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html">https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ExecutorService.html</a></small></p>
</section>
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<h2 id="%E7%BA%BF%E7%A8%8B%E6%B1%A0">线程池？</h2>
<ul>
<li>在面向对象编程中，创建和销毁对象是很费时间的，因为创建一个对象要获取内存资源或者其它更多资源。</li>
<li>在Java中更是如此，虚拟机将试图跟踪每一个对象，以便能够在对象销毁后进行垃圾回收。</li>
<li>所以提高服务程序效率的一个手段就是尽可能减少创建和销毁对象的次数，特别是一些很耗资源的对象创建和销毁。</li>
<li>如何利用已有对象来服务就是一个需要解决的关键问题，其实这就是一些"池化资源"技术产生的原因。</li>
</ul>
</section>
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<h2 id="%E6%88%96%E8%80%85%E5%8F%A6%E4%B8%80%E7%A7%8D%E7%AD%96%E7%95%A5">或者另一种策略</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">FixedThreadPool</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-comment">// Constructor argument is number of threads:</span>
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newFixedThreadPool(<span class="hljs-number">5</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++)
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">LiftOff</span>(<span class="hljs-number">10</span>));
exec.shutdown();
}
}
</code></pre>
<p><small>创建一个固定线程数的线程池，在任何时候最多只有n个线程被创建。如果在所有线程都处于活动状态时，有其他任务提交，他们将等待队列中直到线程可用。如果任何线程由于执行过程中的故障而终止，将会有一个新线程取代这个线程执行后续任务。</small></p>
</section>
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<h2 id="%E7%BA%BF%E7%A8%8B%E6%B1%A0%E5%B8%B8%E8%A7%81%E7%94%A8%E6%B3%95">线程池常见用法</h2>
<ul>
<li>调用<code>Executors</code>类的静态方法<code>newCachedThreadPool</code>或者<code>newFixedThreadPool</code></li>
<li>调用<code>submit</code>提交<code>Runnalbe</code>或<code>Callable</code>对象</li>
<li>保存好返回的<code>Future</code>对象，以便得到结果或者取消任务</li>
<li>当不想再提交任何任务时，调用<code>shutdown</code></li>
</ul>
</section>
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<h1 id="callable"><code>Callable</code></h1>
<p>如果需要获得异步执行的任务结果怎么办？</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-meta">@FunctionalInterface</span>
<span class="hljs-keyword">public</span> <span class="hljs-keyword">interface</span> <span class="hljs-title class_">Callable</span><V>
</code></pre>
<p><small>A task that returns a result and may throw an exception. Implementors define a single method with no arguments called call.<br />
The Callable interface is similar to Runnable, in that both are designed for classes whose instances are potentially executed by another thread. A Runnable, however, does not return a result and cannot throw a checked exception.</small></p>
</section>
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<h1 id="future"><code>Future</code></h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">interface</span> <span class="hljs-title class_">Future</span><V>
</code></pre>
<p><small>A Future represents the result of an asynchronous computation. Methods are provided to check if the computation is complete, to wait for its completion, and to retrieve the result of the computation. The result can only be retrieved using method get when the computation has completed, blocking if necessary until it is ready. Cancellation is performed by the cancel method.</small></p>
</section>
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<h1 id="futurev"><code>Future<V></code></h1>
<p>保存异步计算的结果</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"> V <span class="hljs-title function_">get</span><span class="hljs-params">()</span> <span class="hljs-comment">//阻塞，直到计算完成</span>
V <span class="hljs-title function_">get</span><span class="hljs-params">(<span class="hljs-type">long</span> timeout, TImeUnit unit)</span>
<span class="hljs-keyword">void</span> <span class="hljs-title function_">cancel</span><span class="hljs-params">(<span class="hljs-type">boolean</span> mayInterrupt)</span>
<span class="hljs-type">boolean</span> <span class="hljs-title function_">isCancelled</span><span class="hljs-params">()</span>
<span class="hljs-type">boolean</span> <span class="hljs-title function_">isDone</span><span class="hljs-params">()</span>
</code></pre>
<p><small>当调用<code>Future</code>的<code>get()</code>方法以获得结果时，当前线程就开始阻塞，直接<code>call()</code>方法结束返回结果。</small></p>
</section>
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<h1 id="%E4%B8%BE%E4%BE%8B-2">举例</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">MyCallable</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Callable</span><String>{
<span class="hljs-meta">@Override</span>
<span class="hljs-keyword">public</span> String <span class="hljs-title function_">call</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> Exception {
System.out.println(<span class="hljs-string">"做一些耗时的任务..."</span>);
Thread.sleep(<span class="hljs-number">5000</span>);
<span class="hljs-keyword">return</span> <span class="hljs-string">"OK"</span>;
}
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">FutureSimpleDemo</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> <span class="hljs-keyword">throws</span> InterruptedException, ExecutionException {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">executorService</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
Future<String> future = executorService.submit(<span class="hljs-keyword">new</span> <span class="hljs-title class_">MyCallable</span>());
System.out.println(<span class="hljs-string">"do something..."</span>);
System.out.println(<span class="hljs-string">"得到异步任务返回结果："</span> + future.get());
System.out.println(<span class="hljs-string">"Completed!"</span>);
}
}
</code></pre>
</section>
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<h1 id="sleep-%E7%9D%A1%E7%9C%A0">Sleep 睡眠</h1>
<p><small>Causes the currently executing thread to sleep (temporarily cease execution) for the specified number of milliseconds.</small></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SleepingTask</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">countDown</span> <span class="hljs-operator">=</span> <span class="hljs-number">10</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">while</span> (countDown-- > <span class="hljs-number">0</span>) {
TimeUnit.MILLISECONDS.sleep(<span class="hljs-number">100</span>); <span class="hljs-comment">// Old-style: Thread.sleep(100);</span>
}
} <span class="hljs-keyword">catch</span> (InterruptedException e) { System.err.println(<span class="hljs-string">"Interrupted"</span>); }<span class="hljs-comment">//可能被打断 </span>
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++) { exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SleepingTask</span>()); }
exec.shutdown();
}
}
</code></pre>
</section>
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<h2 id="yield-%E8%AE%A9%E4%BD%8D-%08">Yield 让位 </h2>
<p><small>A hint to the scheduler that the current thread is willing to yield its current use of a processor. The scheduler is free to ignore this hint.</small></p>
<ul>
<li><code>yield</code>和<code>sleep</code>的主要区别：
<ul>
<li><small>yield会临时暂停当前线程，让有同样优先级的正在等待的线程有机会执行</small></li>
<li><small>若没有正在等待的线程或者所有正在等待的线程的优先级都较低，则继续运行</small></li>
<li><small>执行yield的线程何时继续运行由线程调度器来决定，不同厂商可能有不同行为</small></li>
<li><small>yield方法不保证当前的线程会暂停或者停止，但是可以保证当前线程在调用yield方法时会放弃CPU</small></li>
</ul>
</li>
</ul>
</section>
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<h2 id="priority-%E4%BC%98%E5%85%88%E7%BA%A7">Priority 优先级</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SimplePriorities</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">countDown</span> <span class="hljs-operator">=</span> <span class="hljs-number">5</span>;
<span class="hljs-keyword">private</span> <span class="hljs-keyword">volatile</span> <span class="hljs-type">double</span> d; <span class="hljs-comment">// No optimization 后面再解释</span>
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> priority;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">SimplePriorities</span><span class="hljs-params">(<span class="hljs-type">int</span> priority)</span> {
<span class="hljs-built_in">this</span>.priority = priority;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
Thread.currentThread().setPriority(priority);
<span class="hljs-keyword">while</span> (<span class="hljs-literal">true</span>) {
<span class="hljs-comment">// An expensive, interruptable operation:</span>
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">1</span>; i < <span class="hljs-number">100000</span>; i++) {
d += (Math.PI + Math.E) / (<span class="hljs-type">double</span>) i;
<span class="hljs-keyword">if</span> (i % <span class="hljs-number">1000</span> == <span class="hljs-number">0</span>)
Thread.<span class="hljs-keyword">yield</span>();
}
System.out.println(<span class="hljs-built_in">this</span>);
<span class="hljs-keyword">if</span> (--countDown == <span class="hljs-number">0</span>) <span class="hljs-keyword">return</span>;
}
}
</code></pre>
</section>
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<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"> <span class="hljs-keyword">public</span> String <span class="hljs-title function_">toString</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">return</span> Thread.currentThread() + <span class="hljs-string">": "</span> + countDown;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">5</span>; i++)
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SimplePriorities</span>(Thread.MIN_PRIORITY));
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SimplePriorities</span>(Thread.MAX_PRIORITY));
exec.shutdown();
}
}
</code></pre>
<p>改变线程优先级这件事可以做，但尽量不要做</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="27" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="27" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="daemon-%E7%BA%BF%E7%A8%8B">Daemon 线程</h2>
<p><small>A daemon thread is a thread that does not prevent the JVM from exiting when the program finishes but the thread is still running. An example for a daemon thread is the garbage collection.</small></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SimpleDaemons</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">while</span> (<span class="hljs-literal">true</span>) {
TimeUnit.MILLISECONDS.sleep(<span class="hljs-number">100</span>);
System.out.println(Thread.currentThread() + <span class="hljs-string">" "</span> + <span class="hljs-built_in">this</span>);
}
} <span class="hljs-keyword">catch</span> (InterruptedException e) {
System.out.println(<span class="hljs-string">"sleep() interrupted"</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="28" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="28" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"> <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> <span class="hljs-keyword">throws</span> Exception {
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++) {
<span class="hljs-type">Thread</span> <span class="hljs-variable">daemon</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Thread</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SimpleDaemons</span>());
daemon.setDaemon(<span class="hljs-literal">true</span>); <span class="hljs-comment">// Must call before start()</span>
daemon.start();
}
System.out.println(<span class="hljs-string">"All daemons started"</span>);
TimeUnit.MILLISECONDS.sleep(<span class="hljs-number">99</span>);
}
}
</code></pre>
<p>后台运行线程，当所有非后台线程结束时，应用退出，所有Daemon线程被杀！</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="29" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="29" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E5%B0%8F%E7%BB%93">小结</h2>
<ul>
<li>
<p>Java关于线程编程的抽象</p>
<ul>
<li>Thread对象像是运载火箭，Runnable的实现对象就是一个荷载（payload）</li>
<li>Runnable/Callable --> Task</li>
<li>Thread --> let tasks go</li>
</ul>
</li>
</ul>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="30" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="30" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<p><br /><br /><br /><br /><br />
<br /></p>
<div align="center" style="font-size:60px;">中级篇</div>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="31" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="31" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E5%AE%9A%E4%B9%89%E4%B8%80%E4%B8%AA%E6%99%AE%E9%80%9A%E7%BA%BF%E7%A8%8B">定义一个普通线程</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Sleeper</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Thread</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> duration;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">Sleeper</span><span class="hljs-params">(String name, <span class="hljs-type">int</span> sleepTime)</span> {
<span class="hljs-built_in">super</span>(name);
duration = sleepTime;
start();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">try</span> {
sleep(duration);
} <span class="hljs-keyword">catch</span> (InterruptedException e) {
System.out.println(getName() + <span class="hljs-string">" was interrupted."</span>);
<span class="hljs-keyword">return</span>;
}
System.out.println(getName() + <span class="hljs-string">" has awakened"</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="32" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="32" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E5%AE%9A%E4%B8%80%E4%B8%AA%E7%AD%89%E5%BE%85%E7%BA%BF%E7%A8%8B">定一个等待线程</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Joiner</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Thread</span> {
<span class="hljs-keyword">private</span> Sleeper sleeper;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">Joiner</span><span class="hljs-params">(String name, Sleeper sleeper)</span> {
<span class="hljs-built_in">super</span>(name);
<span class="hljs-built_in">this</span>.sleeper = sleeper;
start();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">try</span> {
sleeper.join();
} <span class="hljs-keyword">catch</span> (InterruptedException e) {
System.out.println(<span class="hljs-string">"Interrupted"</span>);
}
System.out.println(getName() + <span class="hljs-string">" join completed"</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="33" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="33" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="join">Join</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">Joining</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">Sleeper</span> <span class="hljs-variable">sleepy</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Sleeper</span>(<span class="hljs-string">"Sleepy"</span>, <span class="hljs-number">1500</span>),
grumpy = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Sleeper</span>(<span class="hljs-string">"Grumpy"</span>, <span class="hljs-number">1500</span>);
<span class="hljs-type">Joiner</span> <span class="hljs-variable">dopey</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Joiner</span>(<span class="hljs-string">"Dopey"</span>, sleepy),
doc = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Joiner</span>(<span class="hljs-string">"Doc"</span>, grumpy);
grumpy.interrupt();
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code>Grumpy was interrupted.
Doc join completed
Sleepy has awakened
Dopey join completed
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="34" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="34" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="exceptions-in-threads">Exceptions in Threads</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">ExceptionThread</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">RuntimeException</span>();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ExceptionThread</span>());
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="35" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="35" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="uncaught-exceptions">Uncaught Exceptions</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">NaiveExceptionHandling</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-keyword">try</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ExceptionThread</span>());
exec.shutdown();
} <span class="hljs-keyword">catch</span> (RuntimeException ue) {
System.out.println(<span class="hljs-string">"Exception has been handled!"</span>); <span class="hljs-comment">// This statement will NOT execute!</span>
}
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code>Exception in thread "pool-1-thread-1" java.lang.RuntimeException
at concurrency.ExceptionThread.run(ExceptionThread.java:7)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="36" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="36" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="uncaughtexceptionhandler">UncaughtExceptionHandler</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">ExceptionThread2</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-type">Thread</span> <span class="hljs-variable">t</span> <span class="hljs-operator">=</span> Thread.currentThread();
System.out.println(<span class="hljs-string">"run() by "</span> + t);
System.out.println( <span class="hljs-string">"eh = "</span> + t.getUncaughtExceptionHandler());
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">RuntimeException</span>();
}
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">MyUncaughtExceptionHandler</span> <span class="hljs-keyword">implements</span>
<span class="hljs-title class_">Thread</span>.UncaughtExceptionHandler {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">uncaughtException</span><span class="hljs-params">(Thread t, Throwable e)</span> {
System.out.println(<span class="hljs-string">"caught "</span> + e);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="37" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="37" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="then">Then</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">HandlerThreadFactory</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">ThreadFactory</span> {
<span class="hljs-keyword">public</span> Thread <span class="hljs-title function_">newThread</span><span class="hljs-params">(Runnable r)</span> {
System.out.println(<span class="hljs-built_in">this</span> + <span class="hljs-string">" creating new Thread"</span>);
<span class="hljs-type">Thread</span> <span class="hljs-variable">t</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Thread</span>(r);
System.out.println(<span class="hljs-string">"created "</span> + t);
t.setUncaughtExceptionHandler(<span class="hljs-keyword">new</span> <span class="hljs-title class_">MyUncaughtExceptionHandler</span>());
System.out.println( <span class="hljs-string">"eh = "</span> + t.getUncaughtExceptionHandler());
<span class="hljs-keyword">return</span> t;
}
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">CaptureUncaughtException</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool(<span class="hljs-keyword">new</span> <span class="hljs-title class_">HandlerThreadFactory</span>());
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ExceptionThread2</span>());
exec.shutdown();
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="38" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="38" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E6%88%96%E8%80%85%E7%AE%80%E5%8D%95%E4%B8%80%E7%82%B9">或者简单一点</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SettingDefaultHandler</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
Thread.setDefaultUncaughtExceptionHandler(
<span class="hljs-keyword">new</span> <span class="hljs-title class_">MyUncaughtExceptionHandler</span>());
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ExceptionThread</span>());
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="39" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="39" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E8%B5%84%E6%BA%90%E5%85%B1%E4%BA%AB%E9%97%AE%E9%A2%98">资源共享问题</h2>
<p>葫芦娃在二维空间中可以随意走，多个葫芦娃在空间上如果随意走，那就会撞头。</p>
<p>因为一个空间位置，是不能共享的。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="40" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="40" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E7%A4%BA%E4%BE%8Bevengenerator">示例：EvenGenerator</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">abstract</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">IntGenerator</span> {
<span class="hljs-keyword">private</span> <span class="hljs-keyword">volatile</span> <span class="hljs-type">boolean</span> <span class="hljs-variable">canceled</span> <span class="hljs-operator">=</span> <span class="hljs-literal">false</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">abstract</span> <span class="hljs-type">int</span> <span class="hljs-title function_">next</span><span class="hljs-params">()</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">cancel</span><span class="hljs-params">()</span> { canceled = <span class="hljs-literal">true</span>; }
<span class="hljs-keyword">public</span> <span class="hljs-type">boolean</span> <span class="hljs-title function_">isCanceled</span><span class="hljs-params">()</span> { <span class="hljs-keyword">return</span> canceled; }
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">EvenGenerator</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">IntGenerator</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">currentEvenValue</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">public</span> <span class="hljs-type">int</span> <span class="hljs-title function_">next</span><span class="hljs-params">()</span> {
++currentEvenValue; <span class="hljs-comment">// Danger point here!</span>
++currentEvenValue;
<span class="hljs-keyword">return</span> currentEvenValue;
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="41" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="41" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<p>EvenChecker</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">EvenChecker</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">private</span> IntGenerator generator;
<span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> <span class="hljs-type">int</span> id;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">EvenChecker</span><span class="hljs-params">(IntGenerator g, <span class="hljs-type">int</span> ident)</span> {
generator = g; id = ident;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">while</span> (!generator.isCanceled()) {
<span class="hljs-type">int</span> <span class="hljs-variable">val</span> <span class="hljs-operator">=</span> generator.next();
<span class="hljs-keyword">if</span> (val % <span class="hljs-number">2</span> != <span class="hljs-number">0</span>) {
System.out.println(val + <span class="hljs-string">" not even!"</span>); generator.cancel(); <span class="hljs-comment">// Cancels all EvenCheckers</span>
}
}
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">test</span><span class="hljs-params">(IntGenerator gp, <span class="hljs-type">int</span> count)</span> {
System.out.println(<span class="hljs-string">"Press Control-C to exit"</span>);
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < count; i++) { exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">EvenChecker</span>(gp, i));}
exec.shutdown();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
EvenChecker.test(<span class="hljs-keyword">new</span> <span class="hljs-title class_">EvenGenerator</span>(), <span class="hljs-number">10</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="42" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="42" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E9%97%AE%E9%A2%98">问题</h1>
<p>In a multi-threaded environment, a <a href="https://en.wikipedia.org/wiki/Race_condition">race condition</a> occurs when two or more threads attempt to update mutable shared data at the same time. Java offers a mechanism to avoid race conditions by synchronizing thread access to shared data.</p>
<p>对资源加锁，使得对资源的访问顺序化，确保在某一时刻只有一个任务在使用共享资源（使其互斥）</p>
<p>Mutual Exclusion （Mutex）</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="43" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="43" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="lock">Lock</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">MutexEvenGenerator</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">IntGenerator</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">currentEvenValue</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">private</span> <span class="hljs-type">Lock</span> <span class="hljs-variable">lock</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReentrantLock</span>();
<span class="hljs-keyword">public</span> <span class="hljs-type">int</span> <span class="hljs-title function_">next</span><span class="hljs-params">()</span> {
<span class="hljs-comment">//加锁</span>
lock.lock(); <span class="hljs-comment">// block until condition holds</span>
<span class="hljs-keyword">try</span> {
++currentEvenValue;
Thread.<span class="hljs-keyword">yield</span>();
++currentEvenValue;
<span class="hljs-keyword">return</span> currentEvenValue;
} <span class="hljs-keyword">finally</span> {
lock.unlock(); <span class="hljs-comment">//一定要用try-catch的finally去释放锁</span>
}
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
EvenChecker.test(<span class="hljs-keyword">new</span> <span class="hljs-title class_">MutexEvenGenerator</span>(), <span class="hljs-number">10</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="44" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="44" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="reentrantlock"><code>ReentrantLock</code></h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">ReentrantLock</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Object</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Lock</span>, Serializable
</code></pre>
<p><small>A ReentrantLock is owned by the thread last successfully locking, but not yet unlocking it. A thread invoking <code>lock</code> will return, successfully acquiring the lock, when the lock is not owned by another thread. The method will return immediately if the current thread already owns the lock. </small></p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"> <span class="hljs-keyword">if</span> (lock.tryLock() ||
lock.tryLock(timeout, unit)) {
...
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="45" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="45" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="synchronized">Synchronized</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">SynchronizedEvenGenerator</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">IntGenerator</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">currentEvenValue</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-type">int</span> <span class="hljs-title function_">next</span><span class="hljs-params">()</span> {
++currentEvenValue;
Thread.<span class="hljs-keyword">yield</span>();
++currentEvenValue;
<span class="hljs-keyword">return</span> currentEvenValue;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
EvenChecker.test(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SynchronizedEvenGenerator</span>(), <span class="hljs-number">10</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="46" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="46" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="critical-sections-%E4%B8%B4%E7%95%8C%E5%8C%BA">Critical Sections 临界区</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">synchronized</span>(syncObject){
<span class="hljs-comment">//balabala</span>
}
</code></pre>
<p>加锁代码片段</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="47" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="47" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E7%A4%BA%E4%BE%8B">示例</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">PairManager1</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">PairManager</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">increment</span><span class="hljs-params">()</span> { <span class="hljs-comment">// Synchronize the entire method:</span>
p.incrementX();
p.incrementY();
store(getPair());
}
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">PairManager2</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">PairManager</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">increment</span><span class="hljs-params">()</span> {
Pair temp;
<span class="hljs-keyword">synchronized</span> (<span class="hljs-built_in">this</span>) { <span class="hljs-comment">// Use a critical section:</span>
p.incrementX();
p.incrementY();
temp = getPair();
}
store(temp);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="48" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:30%;" data-marpit-pagination-total="82" data-marpit-advanced-background="background" data-marpit-advanced-background-split="right"><div data-marpit-advanced-background-container="true" data-marpit-advanced-background-direction="horizontal"><figure style="background-image:url("images/8/Object-Monitor-Threads.PNG");background-size:contain;"></figure></div></section></foreignObject><foreignObject width="70%" height="720"><section id="48" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="48" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;--marpit-advanced-background-split:30%;" data-marpit-pagination-total="82" data-marpit-advanced-background="content" data-marpit-advanced-background-split="right">
<h2 id="lock-on-object">Lock on Object</h2>
<p><small>Java的每个对象都关联一个<a href="https://zh.wikipedia.org/wiki/%E7%9B%A3%E8%A6%96%E5%99%A8_(%E7%A8%8B%E5%BA%8F%E5%90%8C%E6%AD%A5%E5%8C%96)">管程</a>（monitor）以实现多个线程执行该对象上同步（synchronized）方法调用时的互斥。一个线程执行这个对象上的同步方法时JVM检查该对象的管程：</small></p>
<ul>
<li><small><small>如果该对象管程未被占有，当前调用线程可获得所有权并被允许执行改方法；</small></small></li>
<li><small><small>如果管程被另一个线程所有，则调用线程需要等待管程被释放。</small></small></li>
</ul>
<p><small>当一个线程完成同步方法调用时，它释放管程所有权，等待该管程的线程被允许执行同步方法。</small></p>
</section>
</foreignObject><foreignObject width="1280" height="720" data-marpit-advanced-background="pseudo"><section data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="48" style="" data-marpit-pagination-total="82" data-marpit-advanced-background="pseudo" data-marpit-advanced-background-split="right"></section></foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="49" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="49" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E4%B8%BE%E4%B8%AA%E4%BE%8B%E5%AD%90">举个例子</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Counter</span>{
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">count</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">Increment</span><span class="hljs-params">()</span> {
<span class="hljs-type">int</span> <span class="hljs-variable">n</span> <span class="hljs-operator">=</span> count;
count = n+<span class="hljs-number">1</span>;
}
}
</code></pre>
<p>如前所述，多个线程并发调用 <code>counter.Increment();</code>时存在竞争(race condition)。</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="50" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="50" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E5%8F%AF%E8%83%BD%E7%9A%84%E7%BB%93%E6%9E%9C">可能的结果</h1>
<table>
<thead>
<tr>
<th style="text-align:left">Thread 1</th>
<th style="text-align:left">Thread 2</th>
<th style="text-align:center">Count</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:left">counter.Increment();</td>
<td style="text-align:left">---</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">n = count; // 0</td>
<td style="text-align:left">---</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">---</td>
<td style="text-align:left">counter.Increment();</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">---</td>
<td style="text-align:left">n = count; // 0</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">---</td>
<td style="text-align:left">count = n + 1; // 1</td>
<td style="text-align:center">1</td>
</tr>
<tr>
<td style="text-align:left">count = n + 1; // 1</td>
<td style="text-align:left">---</td>
<td style="text-align:center">1</td>
</tr>
</tbody>
</table>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="51" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="51" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E4%BD%BF%E4%B9%8Bsynchronized">使之synchronized</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Counter</span>{
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">count</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-title function_">Increment</span><span class="hljs-params">()</span> {
<span class="hljs-type">int</span> <span class="hljs-variable">n</span> <span class="hljs-operator">=</span> count;
count = n+<span class="hljs-number">1</span>;
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="52" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="52" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E6%AD%A3%E7%A1%AE%E7%9A%84%E7%BB%93%E6%9E%9C">正确的结果</h1>
<table>
<thead>
<tr>
<th style="text-align:left">Thread 1</th>
<th style="text-align:left">Thread 2</th>
<th style="text-align:center">Count</th>
</tr>
</thead>
<tbody>
<tr>
<td style="text-align:left">counter.Increment();</td>
<td style="text-align:left">---</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">(acquires the monitor)</td>
<td style="text-align:left">---</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">n = count; // 0</td>
<td style="text-align:left">---</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">---</td>
<td style="text-align:left">counter.Increment();</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">---</td>
<td style="text-align:left">(can't acquire monitor)</td>
<td style="text-align:center">0</td>
</tr>
<tr>
<td style="text-align:left">count = n + 1; // 1</td>
<td style="text-align:left">--- (blocked)</td>
<td style="text-align:center">1</td>
</tr>
<tr>
<td style="text-align:left">(releases the monitor)</td>
<td style="text-align:left">--- (blocked)</td>
<td style="text-align:center">1</td>
</tr>
<tr>
<td style="text-align:left">----------------------</td>
<td style="text-align:left">(acquires the monitor)</td>
<td style="text-align:center">1</td>
</tr>
<tr>
<td style="text-align:left">----------------------</td>
<td style="text-align:left">n = count; // 1</td>
<td style="text-align:center">1</td>
</tr>
<tr>
<td style="text-align:left">---------------</td>
<td style="text-align:left">count = n + 1; // 2</td>
<td style="text-align:center">2</td>
</tr>
<tr>
<td style="text-align:left">--------------------</td>
<td style="text-align:left">(releases the monitor)</td>
<td style="text-align:center">2</td>
</tr>
</tbody>
</table>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="53" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="53" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="%E4%B8%BE%E4%BE%8B%E7%94%9F%E4%BA%A7%E8%80%85%E6%B6%88%E8%B4%B9%E8%80%85">举例：生产者消费者</h1>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Buffer</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">char</span>[] buffer;
<span class="hljs-keyword">private</span> <span class="hljs-type">int</span> <span class="hljs-variable">count</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>, in = <span class="hljs-number">0</span>, out = <span class="hljs-number">0</span>;
Buffer(<span class="hljs-type">int</span> size) {
buffer = <span class="hljs-keyword">new</span> <span class="hljs-title class_">char</span>[size];
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">Put</span><span class="hljs-params">(<span class="hljs-type">char</span> c)</span> {
<span class="hljs-keyword">while</span> (count == buffer.length) ;
System.out.println(<span class="hljs-string">"Producing "</span> + c + <span class="hljs-string">" ..."</span>);
buffer[in] = c;
in = (in + <span class="hljs-number">1</span>) % buffer.length;
count++;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-type">char</span> <span class="hljs-title function_">Get</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">while</span> (count == <span class="hljs-number">0</span>) ;
<span class="hljs-type">char</span> <span class="hljs-variable">c</span> <span class="hljs-operator">=</span> buffer[out];
out = (out + <span class="hljs-number">1</span>) % buffer.length;
count--;
System.out.println(<span class="hljs-string">"Consuming "</span> + c + <span class="hljs-string">" ..."</span>);
<span class="hljs-keyword">return</span> c;
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="54" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="54" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Producer</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Thread</span> {
<span class="hljs-keyword">private</span> Buffer buffer;
Producer(Buffer b) {
buffer = b;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++) {
buffer.Put((<span class="hljs-type">char</span>) (<span class="hljs-string">'A'</span> + i % <span class="hljs-number">26</span>));
}
}
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Consumer</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_">Thread</span> {
<span class="hljs-keyword">private</span> Buffer buffer;
Consumer(Buffer b) {
buffer = b;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">for</span> (<span class="hljs-type">int</span> <span class="hljs-variable">i</span> <span class="hljs-operator">=</span> <span class="hljs-number">0</span>; i < <span class="hljs-number">10</span>; i++) {
buffer.Get();
}
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="55" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="55" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">PC</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> {
<span class="hljs-type">Buffer</span> <span class="hljs-variable">b</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Buffer</span>(<span class="hljs-number">4</span>);
<span class="hljs-type">Producer</span> <span class="hljs-variable">p</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Producer</span>(b);
<span class="hljs-type">Consumer</span> <span class="hljs-variable">c</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Consumer</span>(b);
p.start();
c.start();
}
}
</code></pre>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-bash">Producing A ...
Producing B ...
Producing C ...
Producing D ...
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="56" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="56" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="thread-coordination">Thread coordination</h1>
<p>If buffer is full, wait until consumer gets.</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">Put</span><span class="hljs-params">(<span class="hljs-type">char</span> c)</span> {
<span class="hljs-keyword">while</span>(count == buffer.length) {
<span class="hljs-keyword">try</span> { wait(); }
<span class="hljs-keyword">catch</span> (InterruptedException e) { }
<span class="hljs-keyword">finally</span> { }
}
System.out.println(<span class="hljs-string">"Producing "</span> + c + <span class="hljs-string">" ..."</span>);
buffer[in] = c;
in = (in + <span class="hljs-number">1</span>) % buffer.length;
count++;
notify();
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="57" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="57" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="thread-coordination-1">Thread coordination</h1>
<p>If buffer is empty, wait until producer puts.</p>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-type">char</span> <span class="hljs-title function_">Get</span><span class="hljs-params">()</span> {
<span class="hljs-keyword">while</span> (count == <span class="hljs-number">0</span>) {
<span class="hljs-keyword">try</span> { wait(); }
<span class="hljs-keyword">catch</span> (InterruptedException e) { }
<span class="hljs-keyword">finally</span> { }
}
<span class="hljs-type">char</span> <span class="hljs-variable">c</span> <span class="hljs-operator">=</span> buffer[out];
out = (out + <span class="hljs-number">1</span>) % buffer.length;
count--;
System.out.println(<span class="hljs-string">"Consuming "</span> + c + <span class="hljs-string">" ..."</span>);
notify();
<span class="hljs-keyword">return</span> c;
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="58" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="58" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h1 id="wait--notifynotifyall"><code>wait</code> & <code>notify()</code>/<code>notifyAll()</code></h1>
<p>The <code>wait()</code> method suspends the calling thread and temporarily releases ownership of the monitor (so it allows other threads to acquire the monitor). The suspended thread that called <code>wait()</code> wakes up only when another thread calls <code>notify()</code> or <code>notifyAll()</code> on that object.</p>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="59" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="59" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<h2 id="%E8%BF%98%E6%98%AF%E7%9C%8B%E4%B8%AA%E4%BE%8B%E5%AD%90">还是看个例子</h2>
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Car</span> {
<span class="hljs-keyword">private</span> <span class="hljs-type">boolean</span> <span class="hljs-variable">waxOn</span> <span class="hljs-operator">=</span> <span class="hljs-literal">false</span>;
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">wax</span><span class="hljs-params">()</span> {
System.out.println(<span class="hljs-string">"Wax On by "</span> + Thread.currentThread().getName());
waxOn = <span class="hljs-literal">true</span>;
notifyAll();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">buff</span><span class="hljs-params">()</span> {
System.out.println(<span class="hljs-string">"Wax Off by "</span> + Thread.currentThread().getName());
waxOn = <span class="hljs-literal">false</span>;
notifyAll();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">waitForWaxing</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> InterruptedException {
<span class="hljs-keyword">while</span> (waxOn == <span class="hljs-literal">false</span>)
wait();
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">synchronized</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">waitForBuffing</span><span class="hljs-params">()</span> <span class="hljs-keyword">throws</span> InterruptedException {
<span class="hljs-keyword">while</span> (waxOn == <span class="hljs-literal">true</span>)
wait();
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="60" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="60" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">WaxOn</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">private</span> Car car;
<span class="hljs-keyword">private</span> String name;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">WaxOn</span><span class="hljs-params">(Car c, String name)</span> {
<span class="hljs-built_in">this</span>.car = c;
<span class="hljs-built_in">this</span>.name = name;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
Thread.currentThread().setName(name);
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">while</span> (!Thread.interrupted()) {
car.waitForBuffing();
TimeUnit.MILLISECONDS.sleep(<span class="hljs-number">200</span>);
car.wax();
}
} <span class="hljs-keyword">catch</span> (InterruptedException e) {
System.out.println(<span class="hljs-string">"Exiting via interrupt"</span>);
}
System.out.println(<span class="hljs-string">"Ending Wax On task"</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="61" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="61" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">class</span> <span class="hljs-title class_">WaxOff</span> <span class="hljs-keyword">implements</span> <span class="hljs-title class_">Runnable</span> {
<span class="hljs-keyword">private</span> Car car;
<span class="hljs-keyword">private</span> String name;
<span class="hljs-keyword">public</span> <span class="hljs-title function_">WaxOff</span><span class="hljs-params">(Car c, String name)</span> {
<span class="hljs-built_in">this</span>.car = c;
<span class="hljs-built_in">this</span>.name = name;
}
<span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">run</span><span class="hljs-params">()</span> {
Thread.currentThread().setName(name);
<span class="hljs-keyword">try</span> {
<span class="hljs-keyword">while</span> (!Thread.interrupted()) {
car.waitForWaxing();
TimeUnit.MILLISECONDS.sleep(<span class="hljs-number">500</span>);
car.buff();
}
} <span class="hljs-keyword">catch</span> (InterruptedException e) {
System.out.println(<span class="hljs-string">"Exiting via interrupt"</span>);
}
System.out.println(<span class="hljs-string">"Ending Wax Off task"</span>);
}
}
</code></pre>
</section>
</foreignObject></svg><svg data-marpit-svg="" viewBox="0 0 1280 720"><foreignObject width="1280" height="720"><section id="62" data-paginate="true" data-background-color="#fff" data-theme="gaia" lang="en-US" data-marpit-pagination="62" style="--paginate:true;--background-color:#fff;--theme:gaia;background-color:#fff;background-image:none;" data-marpit-pagination-total="82">
<pre is="marp-pre" data-auto-scaling="downscale-only"><code class="language-java"><span class="hljs-keyword">public</span> <span class="hljs-keyword">class</span> <span class="hljs-title class_">WaxOMatic</span> {
<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title function_">main</span><span class="hljs-params">(String[] args)</span> <span class="hljs-keyword">throws</span> Exception {
<span class="hljs-type">Car</span> <span class="hljs-variable">car</span> <span class="hljs-operator">=</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Car</span>();
<span class="hljs-type">ExecutorService</span> <span class="hljs-variable">exec</span> <span class="hljs-operator">=</span> Executors.newCachedThreadPool();
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WaxOff</span>(car, <span class="hljs-string">"A-OFF"</span>));
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WaxOn</span>(car, <span class="hljs-string">"B-ON"</span>));
exec.execute(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WaxOn</span>(car, <span class="hljs-string">"C-ON"</span>));
TimeUnit.SECONDS.sleep(<span class="hljs-number">5</span>); <span class="hljs-comment">// Run for a while...</span>