Support PostTaskAndReply from a sequenced task.

base/threading/worker_pool.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 "base/threading/worker_pool.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/debug/leak_annotations.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
 #include "base/task_runner.h"
 #include "base/threading/post_task_and_reply_impl.h"
 #include "base/tracked_objects.h"
 
 namespace base {
 
 namespace {
 
-class PostTaskAndReplyWorkerPool : public internal::PostTaskAndReplyImpl {
- public:
-  explicit PostTaskAndReplyWorkerPool(bool task_is_slow)
-      : task_is_slow_(task_is_slow) {
-  }
-  ~PostTaskAndReplyWorkerPool() override = default;
-
- private:
-  bool PostTask(const tracked_objects::Location& from_here,
-                const Closure& task) override {
-    return WorkerPool::PostTask(from_here, task, task_is_slow_);
-  }
-
-  bool task_is_slow_;
-};
-
 // WorkerPoolTaskRunner ---------------------------------------------
 // A TaskRunner which posts tasks to a WorkerPool with a
 // fixed ShutdownBehavior.
 //
 // Note that this class is RefCountedThreadSafe (inherited from TaskRunner).
 class WorkerPoolTaskRunner : public TaskRunner {
  public:
   explicit WorkerPoolTaskRunner(bool tasks_are_slow);
 
   // TaskRunner implementation
@@ skipping 60 matching lines @@
 bool WorkerPool::PostTaskAndReply(const tracked_objects::Location& from_here,
                                   const Closure& task,
                                   const Closure& reply,
                                   bool task_is_slow) {
   // Do not report PostTaskAndReplyRelay leaks in tests. There's nothing we can
   // do about them because WorkerPool doesn't have a flushing API.
   // http://crbug.com/248513
   // http://crbug.com/290897
   // Note: this annotation does not cover tasks posted through a TaskRunner.
   ANNOTATE_SCOPED_MEMORY_LEAK;
-  return PostTaskAndReplyWorkerPool(task_is_slow).PostTaskAndReply(
-      from_here, task, reply);
+  return internal::PostTaskAndReply(
+      from_here, task, reply,
+      Bind(
+          [](bool task_is_slow, const tracked_objects::Location& from_here,

[gab, 2016/07/25 17:57:44]

I think you can bind |task_is_slow| by value in the [] here (ref. lambda
capture) and forgo the piping trick below.

I guess whether that's allowed depends on one's interpretation of the "Lambda
Expressions" section @ https://chromium-cpp.appspot.com/

Turns out Dana is a great reference in this domain :-)

[fdoray, 2016/07/25 20:40:04]

I think this code
https://cs.chromium.org/chromium/src/base/bind_internal.h?q=bind_internal.h&s...
prevents me to use base::Bind with a lambda that captures variables. And I don't
know how to convert a lambda to a base::Callback without base::Bind.

+             const Closure& task) {
+            return WorkerPool::PostTask(from_here, task, task_is_slow);
+          },
+          task_is_slow));
 }
 
 // static
 const scoped_refptr<TaskRunner>&
 WorkerPool::GetTaskRunner(bool tasks_are_slow) {
   return g_taskrunners.Get().taskrunners_[tasks_are_slow];
 }
 
 }  // namespace base