Pass Callback to TaskRunner by value and consume it on invocation (1)

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 <utility>
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/debug/leak_annotations.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_);
+                Closure task) override {
+    return WorkerPool::PostTask(from_here, std::move(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
   bool PostDelayedTask(const tracked_objects::Location& from_here,
-                       const Closure& task,
+                       Closure task,
                        TimeDelta delay) override;
   bool RunsTasksOnCurrentThread() const override;
 
  private:
   ~WorkerPoolTaskRunner() override;
 
   // Helper function for posting a delayed task. Asserts that the delay is
   // zero because non-zero delays are not supported.
   bool PostDelayedTaskAssertZeroDelay(
       const tracked_objects::Location& from_here,
-      const Closure& task,
+      Closure task,
       base::TimeDelta delay);
 
   const bool tasks_are_slow_;
 
   DISALLOW_COPY_AND_ASSIGN(WorkerPoolTaskRunner);
 };
 
 WorkerPoolTaskRunner::WorkerPoolTaskRunner(bool tasks_are_slow)
     : tasks_are_slow_(tasks_are_slow) {
 }
 
 WorkerPoolTaskRunner::~WorkerPoolTaskRunner() {
 }
 
 bool WorkerPoolTaskRunner::PostDelayedTask(
     const tracked_objects::Location& from_here,
-    const Closure& task,
+    Closure task,
     TimeDelta delay) {
-  return PostDelayedTaskAssertZeroDelay(from_here, task, delay);
+  return PostDelayedTaskAssertZeroDelay(from_here, std::move(task), delay);
 }
 
 bool WorkerPoolTaskRunner::RunsTasksOnCurrentThread() const {
   return WorkerPool::RunsTasksOnCurrentThread();
 }
 
 bool WorkerPoolTaskRunner::PostDelayedTaskAssertZeroDelay(
     const tracked_objects::Location& from_here,
-    const Closure& task,
+    Closure task,
     base::TimeDelta delay) {
   DCHECK_EQ(delay.InMillisecondsRoundedUp(), 0)
       << "WorkerPoolTaskRunner does not support non-zero delays";
-  return WorkerPool::PostTask(from_here, task, tasks_are_slow_);
+  return WorkerPool::PostTask(from_here, std::move(task), tasks_are_slow_);
 }
 
 struct TaskRunnerHolder {
   TaskRunnerHolder() {
     taskrunners_[0] = new WorkerPoolTaskRunner(false);
     taskrunners_[1] = new WorkerPoolTaskRunner(true);
   }
   scoped_refptr<TaskRunner> taskrunners_[2];
 };
 
@@ skipping 14 matching lines @@
 }
 
 // static
 const scoped_refptr<TaskRunner>&
 WorkerPool::GetTaskRunner(bool tasks_are_slow) {
   static auto* task_runner_holder = new TaskRunnerHolder();
   return task_runner_holder->taskrunners_[tasks_are_slow];
 }
 
 }  // namespace base