Implement idle task scheduling.

Source/platform/scheduler/Scheduler.cpp

 // 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.
 
 #include "config.h"
 #include "platform/scheduler/Scheduler.h"
 
 #include "platform/PlatformThreadData.h"
 #include "platform/Task.h"
 #include "platform/ThreadTimers.h"
 #include "platform/TraceEvent.h"
 #include "public/platform/Platform.h"
 #include "wtf/MainThread.h"
 
 namespace blink {
 
 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.
 // Note if the scheduler gets shutdown, this may be run after.
 class Scheduler::MainThreadPendingHighPriorityTaskRunner : public WebThread::Task {
 public:
     MainThreadPendingHighPriorityTaskRunner()
     {
         ASSERT(Scheduler::shared());
     }
@@ skipping 21 matching lines @@
         const Scheduler::Task& task, const TraceLocation& location, const char* traceName)
         : m_task(task, location, traceName)
     {
         ASSERT(Scheduler::shared());
     }
 
     // WebThread::Task implementation.
     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(const TracedIdleTask& idleTask)
+        : m_idleTask(idleTask)
+    {
+        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();
+
+            if (scheduler->canRunIdleTask()) {
+                m_idleTask.run();
+                // Run the next idle task if possible.
+                scheduler->maybePostMainThreadPendingIdleTask();
+            } else {
+                scheduler->repostIdleTaskAtFront(m_idleTask);

[alexclarke, 2014/09/30 15:47:51]

It seems complex to pop and then repost the task if we can't run it.  Why not do
the pop here if scheduler->canRunIdleTask() is true?

[Sami, 2014/09/30 16:14:47]

Yeah, that seems simpler. Just need to be careful about locking and re-entrancy.

[rmcilroy, 2014/10/03 09:40:24]

Make sense, done.

+            }
+        }
+    }
+
+private:
+    TracedIdleTask m_idleTask;
+};
+
+
 Scheduler* Scheduler::s_sharedScheduler = nullptr;
 
 void Scheduler::initializeOnMainThread()
 {
     s_sharedScheduler = new Scheduler();
 }
 
 void Scheduler::shutdown()
 {
     delete s_sharedScheduler;
     s_sharedScheduler = nullptr;
 }
 
 Scheduler* Scheduler::shared()
 {
     return s_sharedScheduler;
 }
 
 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)
 {
 }
 
 Scheduler::~Scheduler()
 {
     while (hasPendingHighPriorityWork()) {
         swapQueuesAndRunPendingTasks();
     }
 }
 
-void Scheduler::willBeginFrame(const WebBeginFrameArgs& args)
+void Scheduler::willBeginFrame(double frameDeadlineSeconds)
 {
-    // TODO: Use frame deadline and interval to schedule idle tasks.
+    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));
+    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"));
 }
 
 void Scheduler::postInputTask(const TraceLocation& location, const Task& task)
 {
     postHighPriorityTaskInternal(location, task, "Scheduler::InputTask");
 }
 
 void Scheduler::didReceiveInputEvent()
 {
     enterSchedulerPolicy(CompositorPriority);
 }
 
 void Scheduler::postCompositorTask(const TraceLocation& location, const Task& task)
 {
     postHighPriorityTaskInternal(location, task, "Scheduler::CompositorTask");
 }
 
 void Scheduler::postIpcTask(const TraceLocation& location, const Task& task)
 {
     // FIXME: we want IPCs to be high priority, but we can't currently do that because some of them can take a very long
     // time to process. These need refactoring but we need to add some infrastructure to identify them.
     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());
     if (m_highPriorityTaskRunnerPosted)
         return;
     m_mainThread->postTask(new MainThreadPendingHighPriorityTaskRunner());
     m_highPriorityTaskRunnerPosted = true;
 }
 
-void Scheduler::postIdleTask(const TraceLocation& location, const IdleTask& idleTask)
+bool Scheduler::maybePostMainThreadPendingIdleTask()
 {
-    scheduleIdleTask(location, idleTask);
+    TRACE_EVENT0("blink", "Scheduler::maybePostMainThreadPendingIdleTask");
+    if (canRunIdleTask()) {
+        Locker<Mutex> lock(m_pendingTasksMutex);
+        if (!m_pendingIdleTasks.isEmpty()) {
+            m_mainThread->postTask(new MainThreadPendingIdleTaskRunner(m_pendingIdleTasks.takeFirst()));
+            return true;
+        }
+    }
+    return false;
 }
 
 void Scheduler::tickSharedTimer()
 {
     TRACE_EVENT0("blink", "Scheduler::tickSharedTimer");
 
     // Run any high priority tasks that are queued up, otherwise the blink timers will yield immediately.
     bool workDone = runPendingHighPriorityTasksIfInCompositorPriority();
     m_sharedTimerFunction();
 
@@ skipping 12 matching lines @@
     return swapQueuesAndRunPendingTasks();
 }
 
 bool Scheduler::swapQueuesAndRunPendingTasks()
 {
     ASSERT(isMainThread());
 
     // 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);
 }
 
 void Scheduler::swapQueuesRunPendingTasksAndAllowHighPriorityTaskRunnerPosting()
 {
     ASSERT(isMainThread());
 
     // 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();
     executeHighPriorityTasks(highPriorityTasks);
 }
 
 void Scheduler::maybeEnterNormalSchedulerPolicy()
 {
     ASSERT(isMainThread());
     ASSERT(m_pendingTasksMutex.locked());
 
     // Go back to the normal scheduler policy if enough time has elapsed.
     if (schedulerPolicy() == CompositorPriority && Platform::current()->monotonicallyIncreasingTime() > m_compositorPriorityPolicyEndTimeSeconds)
         enterSchedulerPolicyLocked(Normal);
 }
 
-bool Scheduler::executeHighPriorityTasks(Deque<TracedTask>& highPriorityTasks)
+bool Scheduler::executeHighPriorityTasks(Deque<TracedStandardTask>& highPriorityTasks)
 {
     TRACE_EVENT0("blink", "Scheduler::executeHighPriorityTasks");
     int highPriorityTasksExecuted = 0;
     while (!highPriorityTasks.isEmpty()) {
         highPriorityTasks.takeFirst().run();
         highPriorityTasksExecuted++;
     }
 
     int highPriorityTaskCount = atomicSubtract(&m_highPriorityTaskCount, highPriorityTasksExecuted);
     ASSERT_UNUSED(highPriorityTaskCount, highPriorityTaskCount >= 0);
     TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("blink.scheduler"), "PendingHighPriorityTasks", m_highPriorityTaskCount);
     return highPriorityTasksExecuted > 0;
 }
 
+void Scheduler::repostIdleTaskAtFront(const TracedIdleTask& idleTask)
+{
+    Locker<Mutex> lock(m_pendingTasksMutex);
+    // Post at the front since the task didn't get a chance to run.
+    m_pendingIdleTasks.prepend(idleTask);
+}
+
 void Scheduler::sharedTimerAdapter()
 {
     shared()->tickSharedTimer();
 }
 
 void Scheduler::setSharedTimerFiredFunction(void (*function)())
 {
     m_sharedTimerFunction = function;
     blink::Platform::current()->setSharedTimerFiredFunction(function ? &Scheduler::sharedTimerAdapter : nullptr);
 }
@@ skipping 20 matching lines @@
 bool Scheduler::hasPendingHighPriorityWork() const
 {
     // This method is expected to be run on the main thread, but the high priority tasks will be posted by
     // other threads. We could use locks here, but this function is (sometimes) called a lot by
     // ThreadTimers::sharedTimerFiredInternal so we decided to use atomics + barrier loads here which
     // should be cheaper.
     // NOTE it's possible the barrier read is overkill here, since delayed yielding isn't a big deal.
     return acquireLoad(&m_highPriorityTaskCount) != 0;
 }
 
+double Scheduler::currentFrameDeadlineSeconds() const
+{
+    return m_currentFrameDeadlineSeconds;
+}
+
+bool Scheduler::canRunIdleTask() const
+{
+    return m_currentFrameCommitted && (m_currentFrameDeadlineSeconds > Platform::current()->monotonicallyIncreasingTime());
+}
+
 Scheduler::SchedulerPolicy Scheduler::schedulerPolicy() const
 {
     ASSERT(isMainThread());
     // It's important not to miss the transition from normal to low latency mode, otherwise we're likely to
     // delay the processing of input tasks. Since that transition is triggered by a different thread, we
     // need either a lock or a memory barrier, and the memory barrier is probably cheaper.
     return static_cast<SchedulerPolicy>(acquireLoad(&m_schedulerPolicy));
 }
 
 void Scheduler::enterSchedulerPolicy(SchedulerPolicy schedulerPolicy)
 {
     Locker<Mutex> lock(m_pendingTasksMutex);
     enterSchedulerPolicyLocked(schedulerPolicy);
 }
 
 void Scheduler::enterSchedulerPolicyLocked(SchedulerPolicy schedulerPolicy)
 {
     ASSERT(m_pendingTasksMutex.locked());
     if (schedulerPolicy == CompositorPriority)
         m_compositorPriorityPolicyEndTimeSeconds = Platform::current()->monotonicallyIncreasingTime() + kLowSchedulerPolicyAfterTouchTimeSeconds;
 
     releaseStore(&m_schedulerPolicy, schedulerPolicy);
     TRACE_COUNTER1(TRACE_DISABLED_BY_DEFAULT("blink.scheduler"), "SchedulerPolicy", schedulerPolicy);
 }
 
 } // namespace blink