Implement idle task scheduling.

Source/platform/scheduler/Scheduler.h

 // Copyright 2014 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.
 
 #ifndef Scheduler_h
 #define Scheduler_h
 
 #include "platform/PlatformExport.h"
 #include "platform/scheduler/TracedTask.h"
 #include "wtf/DoubleBufferedDeque.h"
 #include "wtf/Functional.h"
 #include "wtf/Noncopyable.h"
+#include "wtf/OwnPtr.h"
 #include "wtf/ThreadingPrimitives.h"
 
 namespace blink {
 class WebThread;
 struct WebBeginFrameArgs;
 
 // The scheduler is an opinionated gateway for arranging work to be run on the
 // main thread. It decides which tasks get priority over others based on a
 // scheduling policy and the overall system state.
 class PLATFORM_EXPORT Scheduler {
@@ skipping 34 matching lines @@
     // get preempted by higher priority work.
     void setSharedTimerFiredFunction(void (*function)());
     void setSharedTimerFireInterval(double);
     void stopSharedTimer();
 
 protected:
     class MainThreadPendingTaskRunner;
     class MainThreadPendingHighPriorityTaskRunner;
     friend class MainThreadPendingTaskRunner;
     friend class MainThreadPendingHighPriorityTaskRunner;
+    friend class TracedIdleTask;
 
     enum SchedulerPolicy {
         Normal,
         CompositorPriority,
     };
 
     Scheduler();
     virtual ~Scheduler();
 
-    void scheduleIdleTask(const TraceLocation&, const IdleTask&);
     void postHighPriorityTaskInternal(const TraceLocation&, const Task&, const char* traceName);
+    void postIdleTaskInternal(const TraceLocation&, const IdleTask&, const char* traceName);
 
     static void sharedTimerAdapter();
 
     // Start of main thread only members -----------------------------------
 
     // Only does work in CompositorPriority mode. Returns true if any work was done.
     bool runPendingHighPriorityTasksIfInCompositorPriority();
 
     // Returns true if any work was done.
     bool swapQueuesAndRunPendingTasks();
 
     void swapQueuesRunPendingTasksAndAllowHighPriorityTaskRunnerPosting();
 
     // Returns true if any work was done.
-    bool executeHighPriorityTasks(Deque<TracedTask>&);
+    bool executeHighPriorityTasks(Deque<OwnPtr<TracedTask> >&);
+
+    // Returns true if any work was done.
+    bool swapQueuesAndRunPendingIdleTasks();
+
+    // Returns true if any work was done.
+    bool executeIdleTasks(Deque<OwnPtr<TracedTask> >&);
+
+    // Reposts all the tasks in idleTasks onto the idle task queue.
+    void repostAllIdleTasks(Deque<OwnPtr<TracedTask> >&);
+
+    // Returns the time in seconds until the current frame deadline expires.
+    double getSecondsUntilFrameDeadline() const;

[Sami, 2014/09/24 14:00:40]

nit: drop the |get|, it's cleaner

[rmcilroy, 2014/09/29 17:42:57]

Done.

 
     // Return the current SchedulerPolicy.
     SchedulerPolicy schedulerPolicy() const;
 
     void maybeEnterNormalSchedulerPolicy();
 
     // Must be called while m_pendingTasksMutex is locked.
     void maybePostMainThreadPendingHighPriorityTaskRunner();
 
     void tickSharedTimer();
 
     void (*m_sharedTimerFunction)();
 
     // End of main thread only members -------------------------------------
 
     bool hasPendingHighPriorityWork() const;
 
     void enterSchedulerPolicyLocked(SchedulerPolicy);
 
     void enterSchedulerPolicy(SchedulerPolicy);
 
     static Scheduler* s_sharedScheduler;
 
     WebThread* m_mainThread;
 
     // This mutex protects calls to the pending task queue, m_highPriorityTaskRunnerPosted and
     // m_compositorPriorityPolicyEndTimeSeconds.
     Mutex m_pendingTasksMutex;
-    DoubleBufferedDeque<TracedTask> m_pendingHighPriorityTasks;
+    DoubleBufferedDeque<OwnPtr<TracedTask> > m_pendingHighPriorityTasks;

[Sami, 2014/09/24 14:00:40]

As of Nico's email to chromium-dev@ yesterday I think we can now finally write
>> here :)

[rmcilroy, 2014/09/29 17:42:57]

Acknowledged.

+    DoubleBufferedDeque<OwnPtr<TracedTask> > m_pendingIdleTasks;
     double m_compositorPriorityPolicyEndTimeSeconds;
 
+    double m_currentFrameDeadlineSeconds;
+
     // Declared volatile as it is atomically incremented.
     volatile int m_highPriorityTaskCount;
 
     bool m_highPriorityTaskRunnerPosted;
 
     // Don't access m_schedulerPolicy directly, use enterSchedulerPolicyLocked and SchedulerPolicy instead.
     volatile int m_schedulerPolicy;
 };
 
 } // namespace blink
 
 #endif // Scheduler_h