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

chrome/browser/after_startup_task_utils.cc

 // Copyright 2015 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 "chrome/browser/after_startup_task_utils.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/lazy_instance.h"
@@ skipping 16 matching lines @@
 
 using content::BrowserThread;
 using content::WebContents;
 using content::WebContentsObserver;
 
 namespace {
 
 struct AfterStartupTask {
   AfterStartupTask(const tracked_objects::Location& from_here,
                    const scoped_refptr<base::TaskRunner>& task_runner,
-                   const base::Closure& task)
-      : from_here(from_here), task_runner(task_runner), task(task) {}
+                   base::Closure task)
+      : from_here(from_here), task_runner(task_runner), task(std::move(task)) {}
   ~AfterStartupTask() {}
 
   const tracked_objects::Location from_here;
   const scoped_refptr<base::TaskRunner> task_runner;
-  const base::Closure task;
+  base::Closure task;
 };
 
 // The flag may be read on any thread, but must only be set on the UI thread.
 base::LazyInstance<base::AtomicFlag>::Leaky g_startup_complete_flag;
 
 // The queue may only be accessed on the UI thread.
 base::LazyInstance<std::deque<AfterStartupTask*>>::Leaky g_after_startup_tasks;
 
 bool IsBrowserStartupComplete() {
   // Be sure to initialize the LazyInstance on the main thread since the flag
   // may only be set on it's initializing thread.
   if (g_startup_complete_flag == nullptr)
     return false;
   return g_startup_complete_flag.Get().IsSet();
 }
 
 void RunTask(std::unique_ptr<AfterStartupTask> queued_task) {
   // We're careful to delete the caller's |task| on the target runner's thread.
   DCHECK(queued_task->task_runner->RunsTasksOnCurrentThread());
-  queued_task->task.Run();
+  std::move(queued_task->task).Run();
 }
 
 void ScheduleTask(std::unique_ptr<AfterStartupTask> queued_task) {
   // Spread their execution over a brief time.
   const int kMinDelaySec = 0;
   const int kMaxDelaySec = 10;
   scoped_refptr<base::TaskRunner> target_runner = queued_task->task_runner;
   tracked_objects::Location from_here = queued_task->from_here;
   target_runner->PostDelayedTask(
       from_here, base::Bind(&RunTask, base::Passed(std::move(queued_task))),
@@ skipping 121 matching lines @@
 AfterStartupTaskUtils::Runner::Runner(
     scoped_refptr<base::TaskRunner> destination_runner)
     : destination_runner_(std::move(destination_runner)) {
   DCHECK(destination_runner_);
 }
 
 AfterStartupTaskUtils::Runner::~Runner() = default;
 
 bool AfterStartupTaskUtils::Runner::PostDelayedTask(
     const tracked_objects::Location& from_here,
-    const base::Closure& task,
+    base::Closure task,
     base::TimeDelta delay) {
   DCHECK(delay.is_zero());
-  AfterStartupTaskUtils::PostTask(from_here, destination_runner_, task);
+  AfterStartupTaskUtils::PostTask(from_here, destination_runner_,
+                                  std::move(task));
   return true;
 }
 
 bool AfterStartupTaskUtils::Runner::RunsTasksOnCurrentThread() const {
   return destination_runner_->RunsTasksOnCurrentThread();
 }
 
 void AfterStartupTaskUtils::StartMonitoringStartup() {
   // The observer is self-deleting.
   (new StartupObserver)->Start();
 }
 
 void AfterStartupTaskUtils::PostTask(
     const tracked_objects::Location& from_here,
     const scoped_refptr<base::TaskRunner>& destination_runner,
-    const base::Closure& task) {
+    base::Closure task) {
   if (IsBrowserStartupComplete()) {
-    destination_runner->PostTask(from_here, task);
+    destination_runner->PostTask(from_here, std::move(task));
     return;
   }
 
   std::unique_ptr<AfterStartupTask> queued_task(
-      new AfterStartupTask(from_here, destination_runner, task));
+      new AfterStartupTask(from_here, destination_runner, std::move(task)));
   QueueTask(std::move(queued_task));
 }
 
 void AfterStartupTaskUtils::SetBrowserStartupIsCompleteForTesting() {
   ::SetBrowserStartupIsComplete();
 }
 
 void AfterStartupTaskUtils::SetBrowserStartupIsComplete() {
   ::SetBrowserStartupIsComplete();
 }
 
 bool AfterStartupTaskUtils::IsBrowserStartupComplete() {
   return ::IsBrowserStartupComplete();
 }
 
 void AfterStartupTaskUtils::UnsafeResetForTesting() {
   DCHECK(g_after_startup_tasks.Get().empty());
   if (!IsBrowserStartupComplete())
     return;
   g_startup_complete_flag.Get().UnsafeResetForTesting();
   DCHECK(!IsBrowserStartupComplete());
 }