subsetting java impl #1

joybestourous · 2023-08-10T18:19:17Z

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s-matyukevich

Looks good, but I have a lot of minor comments.

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancer.java

s-matyukevich · 2023-08-10T19:20:44Z

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancer.java

+
+    if (addresses.size() <= config.subsetSize) return allAddresses;
+    if (config.sortAddresses) {
+      // If we sort, we do so via destination hashcode. This is deterministic but differs from the goland instrumentation.


*golang

I guess we should align on this, not sure how realistic this is, but in theory people may want to combine go a java clients in a single ring.

Agreed, we should align. Do you know how golang does the comparison? How does it determine one address is "less than" or "greater than" another?

I looked into this myself. It looks like Address.Addr is a string, so golang is using simple string comparison. SocketAddress does not have an equivalent, so we'd have to call .toString() which isn't guaranteed to produce the same result. I think if we want to align, we should adjust on the golang side.

so we'd have to call .toString() which isn't guaranteed to produce the same result

Why do you think so? String representation of an IP should be the same in all languages, but hashes could be different.

Because if toString() is not overridden java will print out the class description. For example, the FakeSocketAddress we use here overrides toString() to be the name of the socket address, so we see [[FakeSocketAddress-server0]/{}]. Without that we get [[io.grpc.util.OutlierDetectionLoadBalancerTest$FakeSocketAddress@5ed4bc]/{}]. SocketAddress is abstract and does not have any valuable information for toString to be meaningful, and we can't guarantee all of it's extending classes override toString. Maybe that's still safer than hashcode, but there's no guarantee.

Yes, but can we implement a custom Comparator, which will use string representation of an IP, and use it for sorting? IMO it is much better to add to gRFC that addresses must be sorted by IP rather than by some type of hash and define what hashing function should be used.

Oh, sorry, I got the problem now, so what you are saying is that there is no way to safely get a string representation of an instance of SocketAddress in java? I guess that outside tests it will always be an instance of InetSocketAddress, which should correctly override toString() and the way FakeSocketAddress overrides it is also fine for tests. Can we receive an instance of any other class from the resolver?

Yes that's the problem. InetSocketAddress should be the most common, yeah, but the expectations will break if folks use a custom impl of SocketAddress. In general i'm wary of making assumptions like these because we are accepting any SocketAddress, not only InetSocketAddresses, but I suppose InetSocketAddress is well enough established at this point that it's acceptable to do this and just make sure the assumption is well documented.

s-matyukevich · 2023-08-10T19:29:46Z

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancer.java

+
+    ArrayList<EquivalentAddressGroup>  eaglist = new ArrayList<>();
+
+    for (EquivalentAddressGroup eag : allAddresses.getAddresses()) {


In what cases EquivalentAddressGroup can contain more then 1 address? I think if this happens it will break the current implementation. Maybe we should check for this case and return an error? Or we probably can construct eaglist directly from subset.

Why do you think this would break the current implementation? There is no guarantee that it will contain only one address (if there is, we should convince them to remove the EAG because it honestly is just overcomplicating their entire implementation)

I looked more into it and I think we should treat every EquivalentAddressGroup as a single address.

The description of this class says the following

A group of SocketAddresses that are considered equivalent when channel makes connections. Usually the addresses are addresses resolved from the same host name, and connecting to any of them is equally sufficient. They do have order. An address appears earlier on the list is likely to be tried earlier.

Looks like RoundRobin LB creates a sub-channel per EAG code

DNS resolver creates a EAG per resolved address code

I didn't figure out the use-case when EAG is useful, I think it is used in cases when a resolver can provide multiple addresses to connect to the same host, but I don't understand why this could be useful. Still, looks like the rest of the code treats EAG as a single address and probably should do the same.

Hm okay, I'll make this change because I agree it is more in line with what they have, but I will also file an issue/question with upstream regarding its purpose. To me it honestly looks like it exists solely because it would be annoying to remove.

Ah looks like there is an intended purpose: grpc#5263 (comment)

Good find, this make sense. I think it confirms that we should treat EAG as a single address.

util/src/main/java/io/grpc/util/DeterministicSubsettingLoadBalancer.java

util/src/test/java/io/grpc/util/DeterministicSubsettingLoadBalancerTest.java

6efa9ee added `volatile` to `attributes` after TSAN detected a data race that was added in 91d15ce. The race was because attributes may be read from another thread after `transportReady()`, and the post-filtering assignment occurred after `transportReady()`. The code now filters the attributes separately so they are updated before calling `transportReady()`. Original TSAN failure: ``` Read of size 4 at 0x0000cd44769c by thread T23: #0 io.grpc.netty.NettyClientHandler.getAttributes()Lio/grpc/Attributes; NettyClientHandler.java:327 #1 io.grpc.netty.NettyClientTransport.getAttributes()Lio/grpc/Attributes; NettyClientTransport.java:363 #2 io.grpc.netty.NettyClientTransport.newStream(Lio/grpc/MethodDescriptor;Lio/grpc/Metadata;Lio/grpc/CallOptions;[Lio/grpc/ClientStreamTracer;)Lio/grpc/internal/ClientStream; NettyClientTransport.java:183 grpc#3 io.grpc.internal.MetadataApplierImpl.apply(Lio/grpc/Metadata;)V MetadataApplierImpl.java:74 grpc#4 io.grpc.auth.GoogleAuthLibraryCallCredentials$1.onSuccess(Ljava/util/Map;)V GoogleAuthLibraryCallCredentials.java:141 grpc#5 com.google.auth.oauth2.OAuth2Credentials$FutureCallbackToMetadataCallbackAdapter.onSuccess(Lcom/google/auth/oauth2/OAuth2Credentials$OAuthValue;)V OAuth2Credentials.java:534 grpc#6 com.google.auth.oauth2.OAuth2Credentials$FutureCallbackToMetadataCallbackAdapter.onSuccess(Ljava/lang/Object;)V OAuth2Credentials.java:525 ... Previous write of size 4 at 0x0000cd44769c by thread T24: #0 io.grpc.netty.NettyClientHandler$FrameListener.onSettingsRead(Lio/netty/channel/ChannelHandlerContext;Lio/netty/handler/codec/http2/Http2Settings;)V NettyClientHandler.java:920 #1 io.netty.handler.codec.http2.DefaultHttp2ConnectionDecoder$FrameReadListener.onSettingsRead(Lio/netty/channel/ChannelHandlerContext;Lio/netty/handler/codec/http2/Http2Settings;)V DefaultHttp2ConnectionDecoder.java:515 ... ```

As discovered by TSAN, the adsStream field is not synchronized. ``` WARNING: ThreadSanitizer: data race (pid=1625) Read of size 4 at 0x00009b66fc88 by thread T23 (mutexes: write M0): #0 io.grpc.xds.ControlPlaneClient.isReady()Z ControlPlaneClient.java:203 #1 io.grpc.xds.ControlPlaneClient.readyHandler()V ControlPlaneClient.java:211 #2 io.grpc.xds.ControlPlaneClient$AdsStream.onReady()V ControlPlaneClient.java:328 grpc#3 io.grpc.xds.GrpcXdsTransportFactory$EventHandlerToCallListenerAdapter.onReady()V GrpcXdsTransportFactory.java:145 grpc#4 io.grpc.PartialForwardingClientCallListener.onReady()V PartialForwardingClientCallListener.java:44 grpc#5 io.grpc.ForwardingClientCallListener.onReady()V ForwardingClientCallListener.java:23 grpc#6 io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onReady()V ForwardingClientCallListener.java:40 grpc#7 io.grpc.PartialForwardingClientCallListener.onReady()V PartialForwardingClientCallListener.java:44 grpc#8 io.grpc.ForwardingClientCallListener.onReady()V ForwardingClientCallListener.java:23 grpc#9 io.grpc.ForwardingClientCallListener$SimpleForwardingClientCallListener.onReady()V ForwardingClientCallListener.java:40 grpc#10 io.grpc.internal.DelayedClientCall$DelayedListener.onReady()V DelayedClientCall.java:497 grpc#11 io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamOnReady.runInternal()V ClientCallImpl.java:781 grpc#12 io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamOnReady.runInContext()V ClientCallImpl.java:772 grpc#13 io.grpc.internal.ContextRunnable.run()V ContextRunnable.java:37 grpc#14 io.grpc.internal.SerializingExecutor.run()V SerializingExecutor.java:133 grpc#15 java.util.concurrent.ThreadPoolExecutor.runWorker(Ljava/util/concurrent/ThreadPoolExecutor$Worker;)V ThreadPoolExecutor.java:1130 grpc#16 java.util.concurrent.ThreadPoolExecutor$Worker.run()V ThreadPoolExecutor.java:630 grpc#17 java.lang.Thread.run()V Thread.java:830 grpc#18 (Generated Stub) <null> Previous write of size 4 at 0x00009b66fc88 by thread T4 (mutexes: write M1, write M2, write M3, write M4, write M5): #0 io.grpc.xds.ControlPlaneClient$AdsStream.cleanUp()V ControlPlaneClient.java:424 #1 io.grpc.xds.ControlPlaneClient$AdsStream.close(Ljava/lang/Exception;)V ControlPlaneClient.java:418 #2 io.grpc.xds.ControlPlaneClient$1.run()V ControlPlaneClient.java:130 grpc#3 io.grpc.SynchronizationContext.drain()V SynchronizationContext.java:94 grpc#4 io.grpc.SynchronizationContext.execute(Ljava/lang/Runnable;)V SynchronizationContext.java:126 grpc#5 io.grpc.xds.XdsClientImpl.shutdown()V XdsClientImpl.java:207 grpc#6 io.grpc.xds.SharedXdsClientPoolProvider$RefCountedXdsClientObjectPool.returnObject(Ljava/lang/Object;)Lio/grpc/xds/XdsClient; SharedXdsClientPoolProvider.java:144 grpc#7 io.grpc.xds.SharedXdsClientPoolProvider$RefCountedXdsClientObjectPool.returnObject(Ljava/lang/Object;)Ljava/lang/Object; SharedXdsClientPoolProvider.java:102 grpc#8 io.grpc.xds.XdsClientFederationTest.cleanUp()V XdsClientFederationTest.java:86 ```

joybestourous added 6 commits August 1, 2023 15:01

API, Provider, but no full impl yet

477f051

subset implementation

f1dd2f8

provider test

4058b5b

suppresswarnings

5782386

LBRT

2276082

testing

10fdbac

s-matyukevich reviewed Aug 10, 2023

View reviewed changes

joybestourous added 19 commits August 14, 2023 17:56

small fixes

6962789

remove DeterministicSubsettingSubchannel

944d80f

remove ChildHelper

ac6bddf

comments, maxDiff

b7869c4

one eag per addy

ed96951

static

3f9a619

more errors

9260f50

checkstyle

ab4ff7a

fix test

8e8aa9b

checkstyle

5a9e169

checkstyle

1751776

use toString

e31cd3d

use plugin

182e5f7

if {}

0bfd074

final fixes

7fdcfc9

cover uncovered lines with tests

76d686b

formatting

706c6f0

checkstyle

ab30f97

stray space

02433be

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subsetting java impl #1

subsetting java impl #1

joybestourous commented Aug 10, 2023

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s-matyukevich Aug 10, 2023

joybestourous Aug 14, 2023

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s-matyukevich Aug 16, 2023

joybestourous Aug 16, 2023 •

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joybestourous Aug 15, 2023

joybestourous Aug 15, 2023

s-matyukevich Aug 16, 2023


		ArrayList<EquivalentAddressGroup> eaglist = new ArrayList<>();

		for (EquivalentAddressGroup eag : allAddresses.getAddresses()) {

subsetting java impl #1

Are you sure you want to change the base?

subsetting java impl #1

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joybestourous commented Aug 10, 2023

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joybestourous Aug 16, 2023 • edited Loading

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joybestourous Aug 16, 2023 •

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