Implement idle task scheduling.

Source/platform/scheduler/Scheduler.cpp

Index: Source/platform/scheduler/Scheduler.cpp
diff --git a/Source/platform/scheduler/Scheduler.cpp b/Source/platform/scheduler/Scheduler.cpp
index c88c4203a6a7e3c9ad6a36fb3f400e6ea1a7bcc0..218fba7f99afc324cbec7555908e241905852cea 100644
--- a/Source/platform/scheduler/Scheduler.cpp
+++ b/Source/platform/scheduler/Scheduler.cpp
@@ -19,32 +19,6 @@ namespace {
 // The time we should stay in CompositorPriority mode for, after a touch event.
 double kLowSchedulerPolicyAfterTouchTimeSeconds = 0.1;
 
-// Can be created from any thread.
-// Note if the scheduler gets shutdown, this may be run after.
-class MainThreadIdleTaskAdapter : public WebThread::Task {
-public:
-    MainThreadIdleTaskAdapter(const Scheduler::IdleTask& idleTask, double allottedTimeMs, const TraceLocation& location)
-        : m_idleTask(idleTask)
-        , m_allottedTimeMs(allottedTimeMs)
-        , m_location(location)
-    {
-    }
-
-    // WebThread::Task implementation.
-    virtual void run() OVERRIDE
-    {
-        TRACE_EVENT2("blink", "MainThreadIdleTaskAdapter::run",
-            "src_file", m_location.fileName(),
-            "src_func", m_location.functionName());
-        m_idleTask(m_allottedTimeMs);
-    }
-
-private:
-    Scheduler::IdleTask m_idleTask;
-    double m_allottedTimeMs;
-    TraceLocation m_location;
-};
-
 } // namespace
 
 // Typically only created from compositor or render threads.
@@ -86,16 +60,45 @@ public:
     virtual void run() OVERRIDE
     {
         Scheduler* scheduler = Scheduler::shared();
-        // FIXME: This check should't be necessary, tasks should not outlive blink.
+        // FIXME: This check shouldn't be necessary, tasks should not outlive blink.
         ASSERT(scheduler);
         if (scheduler)
-            Scheduler::shared()->runPendingHighPriorityTasksIfInCompositorPriority();
+            scheduler->runPendingHighPriorityTasksIfInCompositorPriority();
+
         m_task.run();
     }
 
-    TracedTask m_task;
+private:
+    TracedStandardTask m_task;
 };
 
+
+// Can be created from any thread.
+// Note if the scheduler gets shutdown, this may be run after.
+class Scheduler::MainThreadPendingIdleTaskRunner : public WebThread::Task {
+public:
+    MainThreadPendingIdleTaskRunner()
+    {
+        ASSERT(Scheduler::shared());
+    }
+
+    // WebThread::Task implementation.
+    virtual void run() OVERRIDE
+    {
+        Scheduler* scheduler = Scheduler::shared();
+        // FIXME: This check shouldn't be necessary, tasks should not outlive blink.
+        ASSERT(scheduler);
+        if (scheduler) {
+            scheduler->runPendingHighPriorityTasksIfInCompositorPriority();

[jochen (gone - plz use gerrit), 2014/10/06 07:33:19]

if we're in compositor priority, why run an idle task next?

[Sami, 2014/10/06 09:48:30]

Right, this call could be removed from here and we could have
maybeRunPendingIdleTask() bail out if there's pending high priority work.

[rmcilroy, 2014/10/06 11:29:42]

The original reason I had this here was in case we change to compositor priority
(or a high prio task is posted) in-between the MainThreadPendingIdleTaskRunner
being posted on the run loop and it being run.  

I just talked to Sami and we decided just to make CanRunIdleTask return false if
when we should yield to high priority tasks (so this task wouldn't get posted).

+            scheduler->maybeRunPendingIdleTask();
+            // If possible, run the next idle task by reposting on the main thread.
+            scheduler->maybePostMainThreadPendingIdleTask();
+        }
+    }
+
+};
+
+
 Scheduler* Scheduler::s_sharedScheduler = nullptr;
 
 void Scheduler::initializeOnMainThread()
@@ -118,6 +121,7 @@ Scheduler::Scheduler()
     : m_sharedTimerFunction(nullptr)
     , m_mainThread(blink::Platform::current()->currentThread())
     , m_compositorPriorityPolicyEndTimeSeconds(0)
+    , m_currentFrameDeadlineSeconds(0)
     , m_highPriorityTaskCount(0)
     , m_highPriorityTaskRunnerPosted(false)
     , m_schedulerPolicy(Normal)
@@ -131,32 +135,37 @@ Scheduler::~Scheduler()
     }
 }
 
-void Scheduler::willBeginFrame(const WebBeginFrameArgs& args)
+void Scheduler::willBeginFrame(double frameDeadlineSeconds)
 {
-    // TODO: Use frame deadline and interval to schedule idle tasks.
+    ASSERT(isMainThread());
+    m_currentFrameCommitted = false;
+    m_currentFrameDeadlineSeconds = frameDeadlineSeconds;
+    // TODO: Schedule a deferred task here to run idle work if didCommitFrameToCompositor never get's called
 }
 
 void Scheduler::didCommitFrameToCompositor()
 {
-    // TODO: Trigger the frame deadline immediately.
-}
-
-void Scheduler::scheduleIdleTask(const TraceLocation& location, const IdleTask& idleTask)
-{
-    // TODO: send a real allottedTime here.
-    m_mainThread->postTask(new MainThreadIdleTaskAdapter(idleTask, 0, location));
+    ASSERT(isMainThread());
+    m_currentFrameCommitted = true;
+    maybePostMainThreadPendingIdleTask();
 }
 
 void Scheduler::postHighPriorityTaskInternal(const TraceLocation& location, const Task& task, const char* traceName)
 {
     Locker<Mutex> lock(m_pendingTasksMutex);
 
-    m_pendingHighPriorityTasks.append(TracedTask(task, location, traceName));
+    m_pendingHighPriorityTasks.append(TracedStandardTask(task, location, traceName));
     atomicIncrement(&m_highPriorityTaskCount);
     maybePostMainThreadPendingHighPriorityTaskRunner();
     TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("blink.scheduler"), "PendingHighPriorityTasks", m_highPriorityTaskCount);
 }
 
+void Scheduler::postIdleTaskInternal(const TraceLocation& location, const IdleTask& idleTask, const char* traceName)
+{
+    Locker<Mutex> lock(m_pendingTasksMutex);
+    m_pendingIdleTasks.append(TracedIdleTask(idleTask, location, traceName));
+}
+
 void Scheduler::postTask(const TraceLocation& location, const Task& task)
 {
     m_mainThread->postTask(new MainThreadPendingTaskRunner(task, location, "Scheduler::MainThreadTask"));
@@ -184,6 +193,11 @@ void Scheduler::postIpcTask(const TraceLocation& location, const Task& task)
     m_mainThread->postTask(new MainThreadPendingTaskRunner(task, location, "Scheduler::IpcTask"));
 }
 
+void Scheduler::postIdleTask(const TraceLocation& location, const IdleTask& idleTask)
+{
+    postIdleTaskInternal(location, idleTask, "Scheduler::IdleTask");
+}
+
 void Scheduler::maybePostMainThreadPendingHighPriorityTaskRunner()
 {
     ASSERT(m_pendingTasksMutex.locked());
@@ -193,9 +207,18 @@ void Scheduler::maybePostMainThreadPendingHighPriorityTaskRunner()
     m_highPriorityTaskRunnerPosted = true;
 }
 
-void Scheduler::postIdleTask(const TraceLocation& location, const IdleTask& idleTask)
+bool Scheduler::maybePostMainThreadPendingIdleTask()
 {
-    scheduleIdleTask(location, idleTask);
+    ASSERT(isMainThread());
+    TRACE_EVENT0("blink", "Scheduler::maybePostMainThreadPendingIdleTask");
+    if (canRunIdleTask()) {
+        Locker<Mutex> lock(m_pendingTasksMutex);
+        if (!m_pendingIdleTasks.isEmpty()) {
+            m_mainThread->postTask(new MainThreadPendingIdleTaskRunner());
+            return true;
+        }
+    }
+    return false;
 }
 
 void Scheduler::tickSharedTimer()
@@ -221,6 +244,23 @@ bool Scheduler::runPendingHighPriorityTasksIfInCompositorPriority()
     return swapQueuesAndRunPendingTasks();
 }
 
+bool Scheduler::maybeRunPendingIdleTask()
+{
+    ASSERT(isMainThread());
+    if (!canRunIdleTask())
+        return false;
+
+    takeFirstPendingIdleTask().run();
+    return true;
+}
+
+TracedIdleTask Scheduler::takeFirstPendingIdleTask()
+{
+    Locker<Mutex> lock(m_pendingTasksMutex);
+    ASSERT(!m_pendingIdleTasks.isEmpty());
+    return m_pendingIdleTasks.takeFirst();
+}
+
 bool Scheduler::swapQueuesAndRunPendingTasks()
 {
     ASSERT(isMainThread());
@@ -228,7 +268,7 @@ bool Scheduler::swapQueuesAndRunPendingTasks()
     // These locks guard against another thread posting input or compositor tasks while we swap the buffers.
     // One the buffers have been swapped we can safely access the returned deque without having to lock.
     m_pendingTasksMutex.lock();
-    Deque<TracedTask>& highPriorityTasks = m_pendingHighPriorityTasks.swapBuffers();
+    Deque<TracedStandardTask>& highPriorityTasks = m_pendingHighPriorityTasks.swapBuffers();
     maybeEnterNormalSchedulerPolicy();
     m_pendingTasksMutex.unlock();
     return executeHighPriorityTasks(highPriorityTasks);
@@ -241,7 +281,7 @@ void Scheduler::swapQueuesRunPendingTasksAndAllowHighPriorityTaskRunnerPosting()
     // These locks guard against another thread posting input or compositor tasks while we swap the buffers.
     // One the buffers have been swapped we can safely access the returned deque without having to lock.
     m_pendingTasksMutex.lock();
-    Deque<TracedTask>& highPriorityTasks = m_pendingHighPriorityTasks.swapBuffers();
+    Deque<TracedStandardTask>& highPriorityTasks = m_pendingHighPriorityTasks.swapBuffers();
     m_highPriorityTaskRunnerPosted = false;
     maybeEnterNormalSchedulerPolicy();
     m_pendingTasksMutex.unlock();
@@ -258,7 +298,7 @@ void Scheduler::maybeEnterNormalSchedulerPolicy()
         enterSchedulerPolicyLocked(Normal);
 }
 
-bool Scheduler::executeHighPriorityTasks(Deque<TracedTask>& highPriorityTasks)
+bool Scheduler::executeHighPriorityTasks(Deque<TracedStandardTask>& highPriorityTasks)
 {
     TRACE_EVENT0("blink", "Scheduler::executeHighPriorityTasks");
     int highPriorityTasksExecuted = 0;
@@ -313,6 +353,19 @@ bool Scheduler::hasPendingHighPriorityWork() const
     return acquireLoad(&m_highPriorityTaskCount) != 0;
 }
 
+double Scheduler::currentFrameDeadlineForIdleTasks() const
+{
+    ASSERT(isMainThread());
+    // TODO: Make idle time more fine-grain chunks when in Compositor priority.
+    return m_currentFrameDeadlineSeconds;
+}
+
+bool Scheduler::canRunIdleTask() const
+{
+    ASSERT(isMainThread());
+    return m_currentFrameCommitted && (m_currentFrameDeadlineSeconds > Platform::current()->monotonicallyIncreasingTime());

[Sami, 2014/10/06 09:48:30]

To jochen's point, should we be checking !shouldYieldForHighPriorityWork() here
too?

[rmcilroy, 2014/10/06 11:29:42]

Done.

+}
+
 Scheduler::SchedulerPolicy Scheduler::schedulerPolicy() const
 {
     ASSERT(isMainThread());