Support PostTaskAndReply from a sequenced task.

base/threading/post_task_and_reply_impl.cc

Index: base/threading/post_task_and_reply_impl.cc
diff --git a/base/threading/post_task_and_reply_impl.cc b/base/threading/post_task_and_reply_impl.cc
index c906866cfb8e61143279a833ed4f5ea04971fb07..d68621c77b008ec9fc766904b34a7a29a5ac483f 100644
--- a/base/threading/post_task_and_reply_impl.cc
+++ b/base/threading/post_task_and_reply_impl.cc
@@ -5,41 +5,42 @@
 #include "base/threading/post_task_and_reply_impl.h"
 
 #include "base/bind.h"
-#include "base/location.h"
-#include "base/single_thread_task_runner.h"
-#include "base/threading/thread_task_runner_handle.h"
+#include "base/callback.h"
+#include "base/logging.h"
+#include "base/memory/ref_counted.h"
+#include "base/sequence_checker.h"
+#include "base/sequenced_task_runner.h"
+#include "base/threading/sequenced_task_runner_handle.h"
 
 namespace base {
 
 namespace {
 
-// This relay class remembers the MessageLoop that it was created on, and
-// ensures that both the |task| and |reply| Closures are deleted on this same
-// thread. Also, |task| is guaranteed to be deleted before |reply| is run or
-// deleted.
+// This relay class remembers the sequence that it was created on, and ensures
+// that both the |task| and |reply| Closures are deleted on this same sequence.
+// Also, |task| is guaranteed to be deleted before |reply| is run or deleted.
 //
-// If this is not possible because the originating MessageLoop is no longer
-// available, the the |task| and |reply| Closures are leaked.  Leaking is
-// considered preferable to having a thread-safetey violations caused by
-// invoking the Closure destructor on the wrong thread.
+// If RunReplyAndSelfDestruct() doesn't run because the originating execution
+// context is no longer available, then the |task| and |reply| Closures are
+// leaked. Leaking is considered preferable to having a thread-safetey
+// violations caused by invoking the Closure destructor on the wrong sequence.
 class PostTaskAndReplyRelay {
  public:
   PostTaskAndReplyRelay(const tracked_objects::Location& from_here,
                         const Closure& task,
                         const Closure& reply)
       : from_here_(from_here),
-        origin_task_runner_(ThreadTaskRunnerHandle::Get()) {
-    task_ = task;
-    reply_ = reply;
-  }
+        origin_task_runner_(SequencedTaskRunnerHandle::Get()),
+        reply_(reply),
+        task_(task) {}
 
   ~PostTaskAndReplyRelay() {
-    DCHECK(origin_task_runner_->BelongsToCurrentThread());
+    DCHECK(sequence_checker_.CalledOnValidSequence());
     task_.Reset();
     reply_.Reset();
   }
 
-  void Run() {
+  void RunTaskAndPostReply() {
     task_.Run();
     origin_task_runner_->PostTask(
         from_here_, Bind(&PostTaskAndReplyRelay::RunReplyAndSelfDestruct,
@@ -48,7 +49,7 @@ class PostTaskAndReplyRelay {
 
  private:
   void RunReplyAndSelfDestruct() {
-    DCHECK(origin_task_runner_->BelongsToCurrentThread());
+    DCHECK(sequence_checker_.CalledOnValidSequence());
 
     // Force |task_| to be released before |reply_| is to ensure that no one
     // accidentally depends on |task_| keeping one of its arguments alive while
@@ -61,8 +62,9 @@ class PostTaskAndReplyRelay {
     delete this;
   }
 
-  tracked_objects::Location from_here_;
-  scoped_refptr<SingleThreadTaskRunner> origin_task_runner_;
+  const SequenceChecker sequence_checker_;
+  const tracked_objects::Location from_here_;
+  const scoped_refptr<SequencedTaskRunner> origin_task_runner_;
   Closure reply_;
   Closure task_;
 };
@@ -75,12 +77,11 @@ bool PostTaskAndReplyImpl::PostTaskAndReply(
     const tracked_objects::Location& from_here,
     const Closure& task,
     const Closure& reply) {
-  // TODO(tzik): Use DCHECK here once the crash is gone. http://crbug.com/541319
-  CHECK(!task.is_null()) << from_here.ToString();
-  CHECK(!reply.is_null()) << from_here.ToString();
+  DCHECK(!task.is_null()) << from_here.ToString();
+  DCHECK(!reply.is_null()) << from_here.ToString();
   PostTaskAndReplyRelay* relay =
       new PostTaskAndReplyRelay(from_here, task, reply);
-  if (!PostTask(from_here, Bind(&PostTaskAndReplyRelay::Run,
+  if (!PostTask(from_here, Bind(&PostTaskAndReplyRelay::RunTaskAndPostReply,
                                 Unretained(relay)))) {
     delete relay;
     return false;