Created HOWITWORKS; cleanup of README

Addresses a request from @chrisboulton in GitHub issue chrisboulton#149

Slight grammar cleanup and content update in README.md
Mention of HOWITWORKS.md in README.md, referring those who want to know more that direction
Expanded and slightly cleaner version of a comment made in chrisboulton#149 that prompted this commit/PR
   was placed in HOWITWORKS.md

Signed-off-by: Daniel Hunsaker <[email protected]>

Author: danhunsaker

HOWITWORKS.md

@@ -0,0 +1,157 @@
+*For an overview of how to __use__ php-resque, see `README.md`.*
+
+The following is a step-by-step breakdown of how php-resque operates.
+
+## Enqueue Job ##
+
+What happens when you call `Resque::enqueue()`?
+
+1. `Resque::enqueue()` calls `Resque_Job::create()` with the same arguments it
+   received.
+2. `Resque_Job::create()` checks that your `$args` (the third argument) are
+   either `null` or in an array
+3. `Resque_Job::create()` generates a job ID (a "token" in most of the docs)
+4. `Resque_Job::create()` pushes the job to the requested queue (first
+   argument)
+5. `Resque_Job::create()`, if status monitoring is enabled for the job (fourth
+   argument), calls `Resque_Job_Status::create()` with the job ID as its only
+   argument
+6. `Resque_Job_Status::create()` creates a key in Redis with the job ID in its
+   name, and the current status (as well as a couple of timestamps) as its
+   value, then returns control to `Resque_Job::create()`
+7. `Resque_Job::create()` returns control to `Resque::enqueue()`, with the job
+   ID as a return value
+8. `Resque::enqueue()` triggers the `afterEnqueue` event, then returns control
+   to your application, again with the job ID as its return value
+
+## Workers At Work ##
+
+How do the workers process the queues?
+
+1. `Resque_Worker::work()`, the main loop of the worker process, calls
+   `Resque_Worker->reserve()` to check for a job
+2. `Resque_Worker->reserve()` checks whether to use blocking pops or not (from
+   `BLOCKING`), then acts accordingly:
+  * Blocking Pop
+    1. `Resque_Worker->reserve()` calls `Resque_Job::reserveBlocking()` with
+       the entire queue list and the timeout (from `INTERVAL`) as arguments
+    2. `Resque_Job::reserveBlocking()` calls `Resque::blpop()` (which in turn
+       calls Redis' `blpop`, after prepping the queue list for the call, then
+       processes the response for consistency with other aspects of the
+       library, before finally returning control [and the queue/content of the
+       retrieved job, if any] to `Resque_Job::reserveBlocking()`)
+    3. `Resque_Job::reserveBlocking()` checks whether the job content is an
+       array (it should contain the job's type [class], payload [args], and
+       ID), and aborts processing if not
+    4. `Resque_Job::reserveBlocking()` creates a new `Resque_Job` object with
+       the queue and content as constructor arguments to initialize the job
+       itself, and returns it, along with control of the process, to
+       `Resque_Worker->reserve()`
+  * Queue Polling
+    1. `Resque_Worker->reserve()` iterates through the queue list, calling
+       `Resque_Job::reserve()` with the current queue's name as the sole
+       argument on each pass
+    2. `Resque_Job::reserve()` passes the queue name on to `Resque::pop()`,
+       which in turn calls Redis' `lpop` with the same argument, then returns
+       control (and the job content, if any) to `Resque_Job::reserve()`
+    3. `Resque_Job::reserve()` checks whether the job content is an array (as
+       before, it should contain the job's type [class], payload [args], and
+       ID), and aborts processing if not
+    4. `Resque_Job::reserve()` creates a new `Resque_Job` object in the same
+       manner as above, and also returns this object (along with control of
+       the process) to `Resque_Worker->reserve()`
+3. In either case, `Resque_Worker->reserve()` returns the new `Resque_Job`
+   object, along with control, up to `Resque_Worker::work()`; if no job is
+   found, it simply returns `FALSE`
+  * No Jobs
+    1. If blocking mode is not enabled, `Resque_Worker::work()` sleeps for
+       `INTERVAL` seconds; it calls `usleep()` for this, so fractional seconds
+       *are* supported
+  * Job Reserved
+    1. `Resque_Worker::work()` triggers a `beforeFork` event
+    2. `Resque_Worker::work()` calls `Resque_Worker->workingOn()` with the new
+       `Resque_Job` object as its argument
+    3. `Resque_Worker->workingOn()` does some reference assignments to help keep
+       track of the worker/job relationship, then updates the job status from
+       `WAITING` to `RUNNING`
+    4. `Resque_Worker->workingOn()` stores the new `Resque_Job` object's payload
+       in a Redis key associated to the worker itself (this is to prevent the job
+       from being lost indefinitely, but does rely on that PID never being
+       allocated on that host to a different worker process), then returns control
+       to `Resque_Worker::work()`
+    5. `Resque_Worker::work()` forks a child process to run the actual `perform()`
+    6. The next steps differ between the worker and the child, now running in
+       separate processes:
+      * Worker
+        1. The worker waits for the job process to complete
+        2. If the exit status is not 0, the worker calls `Resque_Job->fail()` with
+           a `Resque_Job_DirtyExitException` as its only argument.
+        3. `Resque_Job->fail()` triggers an `onFailure` event
+        4. `Resque_Job->fail()` updates the job status from `RUNNING` to `FAILED`
+        5. `Resque_Job->fail()` calls `Resque_Failure::create()` with the job
+           payload, the `Resque_Job_DirtyExitException`, the internal ID of the
+           worker, and the queue name as arguments
+        6. `Resque_Failure::create()` creates a new object of whatever type has
+           been set as the `Resque_Failure` "backend" handler; by default, this is
+           a `Resque_Failure_Redis` object, whose constructor simply collects the
+           data passed into `Resque_Failure::create()` and pushes it into Redis
+           in the `failed` queue
+        7. `Resque_Job->fail()` increments two failure counters in Redis: one for
+           a total count, and one for the worker
+        8. `Resque_Job->fail()` returns control to the worker (still in
+           `Resque_Worker::work()`) without a value
+      * Job
+        1. The job calls `Resque_Worker->perform()` with the `Resque_Job` as its
+           only argument.
+        2. `Resque_Worker->perform()` sets up a `try...catch` block so it can
+           properly handle exceptions by marking jobs as failed (by calling
+           `Resque_Job->fail()`, as above)
+        3. Inside the `try...catch`, `Resque_Worker->perform()` triggers an
+           `afterFork` event
+        4. Still inside the `try...catch`, `Resque_Worker->perform()` calls
+           `Resque_Job->perform()` with no arguments
+        5. `Resque_Job->perform()` calls `Resque_Job->getInstance()` with no
+           arguments
+        6. If `Resque_Job->getInstance()` has already been called, it returns the
+           existing instance; otherwise:
+        7. `Resque_Job->getInstance()` checks that the job's class (type) exists
+           and has a `perform()` method; if not, in either case, it throws an
+           exception which will be caught by `Resque_Worker->perform()`
+        8. `Resque_Job->getInstance()` creates an instance of the job's class, and
+           initializes it with a reference to the `Resque_Job` itself, the job's
+           arguments (which it gets by calling `Resque_Job->getArguments()`, which
+           in turn simply returns the value of `args[0]`, or an empty array if no
+           arguments were passed), and the queue name
+        9. `Resque_Job->getInstance()` returns control, along with the job class
+           instance, to `Resque_Job->perform()`
+        10. `Resque_Job->perform()` sets up its own `try...catch` block to handle
+            `Resque_Job_DontPerform` exceptions; any other exceptions are passed
+            up to `Resque_Worker->perform()`
+        11. `Resque_Job->perform()` triggers a `beforePerform` event
+        12. `Resque_Job->perform()` calls `setUp()` on the instance, if it exists
+        13. `Resque_Job->perform()` calls `perform()` on the instance
+        14. `Resque_Job->perform()` calls `tearDown()` on the instance, if it
+            exists
+        15. `Resque_Job->perform()` triggers an `afterPerform` event
+        16. The `try...catch` block ends, suppressing `Resque_Job_DontPerform`
+            exceptions by returning control, and the value `FALSE`, to
+            `Resque_Worker->perform()`; any other situation returns the value
+            `TRUE` along with control, instead
+        17. The `try...catch` block in `Resque_Worker->perform()` ends
+        18. `Resque_Worker->perform()` updates the job status from `RUNNING` to
+            `COMPLETE`, then returns control, with no value, to the worker (again
+            still in `Resque_Worker::work()`)
+        19. `Resque_Worker::work()` calls `exit(0)` to terminate the job process
+            cleanly
+      * SPECIAL CASE: Non-forking OS (Windows)
+        1. Same as the job above, except it doesn't call `exit(0)` when done
+    7. `Resque_Worker::work()` calls `Resque_Worker->doneWorking()` with no
+       arguments
+    8. `Resque_Worker->doneWorking()` increments two processed counters in Redis:
+       one for a total count, and one for the worker
+    9. `Resque_Worker->doneWorking()` deletes the Redis key set in
+       `Resque_Worker->workingOn()`, then returns control, with no value, to
+       `Resque_Worker::work()`
+4. `Resque_Worker::work()` returns control to the beginning of the main loop,
+   where it will wait for the next job to become available, and start this
+   process all over again