Rewrite media::Pipeline state transition machinery and simplify shutdown.

media/base/serial_runner.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/base/serial_runner.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/message_loop.h"
 #include "base/message_loop_proxy.h"
 
 namespace media {
 
 // Converts a bound function accepting a Closure into a bound function
 // accepting a PipelineStatusCB. Since closures have no way of reporting a
 // status |status_cb| is executed with PIPELINE_OK.
 static void RunBoundClosure(
     const SerialRunner::BoundClosure& bound_closure,
     const PipelineStatusCB& status_cb) {
   bound_closure.Run(base::Bind(status_cb, PIPELINE_OK));
 }
 
-// Runs |status_cb| with |last_status| on |message_loop|, trampolining if
-// necessary.
+// Runs |status_cb| with |last_status| on |message_loop|.
 static void RunOnMessageLoop(
     const scoped_refptr<base::MessageLoopProxy>& message_loop,
     const PipelineStatusCB& status_cb,
     PipelineStatus last_status) {
-  if (!message_loop->BelongsToCurrentThread()) {
-    message_loop->PostTask(FROM_HERE, base::Bind(
-        &RunOnMessageLoop, message_loop, status_cb, last_status));
-    return;
-  }
-  status_cb.Run(last_status);
+  // Force post to permit cancellation of a series in the scenario where all
+  // bound functions run on the same thread.
+  message_loop->PostTask(FROM_HERE, base::Bind(status_cb, last_status));
 }
 
 SerialRunner::Queue::Queue() {}
 SerialRunner::Queue::~Queue() {}
 
 void SerialRunner::Queue::Push(
     const BoundClosure& bound_closure) {
   bound_fns_.push(base::Bind(&RunBoundClosure, bound_closure));
 }
 
@@ skipping 40 matching lines @@
     base::ResetAndReturn(&done_cb_).Run(last_status);
     return;
   }
 
   BoundPipelineStatusCB bound_fn = bound_fns_.Pop();
   bound_fn.Run(base::Bind(&RunOnMessageLoop, message_loop_, base::Bind(
       &SerialRunner::RunNextInSeries, weak_this_.GetWeakPtr())));
 }
 
 }  // namespace media