Prioritizing input and compositor tasks in the blink scheduler.

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 61ae7aef1d486bd618417a2d2d62c14c08db06bc..4788297cae7e8c66e63c9a5e62e6723c610a0309 100644
--- a/Source/platform/scheduler/Scheduler.cpp
+++ b/Source/platform/scheduler/Scheduler.cpp
@@ -5,58 +5,63 @@
 #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 "platform/TraceLocation.h"
 #include "public/platform/Platform.h"
-#include "public/platform/WebThread.h"
+#include "wtf/WeakPtr.h"
 
 namespace blink {
 
 namespace {
 
-class MainThreadTaskAdapter : public blink::WebThread::Task {
+class MainThreadIdleTaskAdapter : public blink::WebThread::Task {
 public:
-    explicit MainThreadTaskAdapter(const TraceLocation& location, const Scheduler::Task& task)
-        : m_location(location)
-        , m_task(task)
+    MainThreadIdleTaskAdapter(const Scheduler::IdleTask& idleTask, double allottedTimeMs)
+        : m_idleTask(idleTask)
+        , m_allottedTimeMs(allottedTimeMs)
     {
     }
 
     // WebThread::Task implementation.
     virtual void run() OVERRIDE
     {
-        TRACE_EVENT2("blink", "MainThreadTaskAdapter::run",
-            "src_file", m_location.fileName(),
-            "src_func", m_location.functionName());
-        m_task();
+        TRACE_EVENT1("blink", "MainThreadIdleTaskAdapter::run", "allottedTime", m_allottedTimeMs);
+        m_idleTask(m_allottedTimeMs);
     }
 
 private:
-    const TraceLocation m_location;
-    Scheduler::Task m_task;
+    Scheduler::IdleTask m_idleTask;
+    double m_allottedTimeMs;
 };
 
-class MainThreadIdleTaskAdapter : public blink::WebThread::Task {
+class MainThreadPendingTaskRunner : public blink::WebThread::Task {
 public:
-    MainThreadIdleTaskAdapter(const Scheduler::IdleTask& idleTask, double allottedTimeMs)
-        : m_idleTask(idleTask)
-        , m_allottedTimeMs(allottedTimeMs)
+    MainThreadPendingTaskRunner()
+        : m_weakPtrFactory(this)
     {
+        s_taskInFlight = m_weakPtrFactory.createWeakPtr();
     }
 
     // WebThread::Task implementation.
     virtual void run() OVERRIDE
     {
-        TRACE_EVENT1("blink", "MainThreadIdleTaskAdapter::run", "allottedTime", m_allottedTimeMs);
-        m_idleTask(m_allottedTimeMs);
+        Scheduler::shared()->runPendingTasks();
+    }
+
+    static bool isTaskInFlight()
+    {
+        return s_taskInFlight;
     }
 
 private:
-    Scheduler::IdleTask m_idleTask;
-    double m_allottedTimeMs;
+    WeakPtrFactory<MainThreadPendingTaskRunner> m_weakPtrFactory;
+
+    static WeakPtr<MainThreadPendingTaskRunner> s_taskInFlight;
 };
 
+WeakPtr<MainThreadPendingTaskRunner> MainThreadPendingTaskRunner::s_taskInFlight;

[Sami, 2014/08/07 14:24:45]

I think we need to avoid non-POD static initializers. There's a DEFINE_GLOBAL
macro if we really need this, but is there a way we could avoid it by maybe
keeping track of whether the task is pending with a normal (atomic) bool?

[alexclarke, 2014/08/07 15:15:29]

Done.

 }
 
 Scheduler* Scheduler::s_sharedScheduler = nullptr;
@@ -85,11 +90,7 @@ Scheduler::Scheduler()
 
 Scheduler::~Scheduler()
 {
-}
-
-void Scheduler::scheduleTask(const TraceLocation& location, const Task& task)
-{
-    m_mainThread->postTask(new MainThreadTaskAdapter(location, task));
+    runPendingTasks();
 }
 
 void Scheduler::scheduleIdleTask(const IdleTask& idleTask)
@@ -100,17 +101,20 @@ void Scheduler::scheduleIdleTask(const IdleTask& idleTask)
 
 void Scheduler::postTask(const TraceLocation& location, const Task& task)
 {
-    scheduleTask(location, task);
+    m_pendingLowPriorityTasks.append(TracedTask(task, location));
+    maybePostTaskLoopOnMainThread();
 }
 
 void Scheduler::postInputTask(const TraceLocation& location, const Task& task)
 {
-    scheduleTask(location, task);
+    m_pendingInputTasks.append(TracedTask(task, location));
+    maybePostTaskLoopOnMainThread();
 }
 
 void Scheduler::postCompositorTask(const TraceLocation& location, const Task& task)
 {
-    scheduleTask(location, task);
+    m_pendingCompositorTasks.append(TracedTask(task, location));
+    maybePostTaskLoopOnMainThread();
 }
 
 void Scheduler::postIdleTask(const IdleTask& idleTask)
@@ -121,7 +125,48 @@ void Scheduler::postIdleTask(const IdleTask& idleTask)
 void Scheduler::tickSharedTimer()
 {
     TRACE_EVENT0("blink", "Scheduler::tickSharedTimer");
+
+    runHighPriorityTasks();
     m_sharedTimerFunction();
+    runHighPriorityTasks();
+}
+
+void Scheduler::runPendingTasks()
+{
+    TRACE_EVENT0("blink", "Scheduler::runPendingTasks");
+
+    // Execute tasks from the queues in order of priority.
+    for (;;) {
+        runHighPriorityTasks();
+
+        if (m_pendingLowPriorityTasks.isEmpty())
+            break;
+        m_pendingLowPriorityTasks.takeFirst().run();
+    }
+}
+
+void Scheduler::runHighPriorityTasks()
+{
+    TRACE_EVENT0("blink", "Scheduler::runHighPriorityTasks");
+
+    for (;;) {
+        if (!m_pendingInputTasks.isEmpty()) {
+            m_pendingInputTasks.takeFirst().run();
+            continue;
+        }
+
+        if (m_pendingCompositorTasks.isEmpty())
+            break;
+        m_pendingCompositorTasks.takeFirst().run();
+    }
+}
+
+void Scheduler::maybePostTaskLoopOnMainThread()
+{
+    if (MainThreadPendingTaskRunner::isTaskInFlight())
+        return;
+
+    m_mainThread->postTask(new MainThreadPendingTaskRunner());
 }
 
 void Scheduler::sharedTimerAdapter()
@@ -147,7 +192,15 @@ void Scheduler::stopSharedTimer()
 
 bool Scheduler::shouldYieldForHighPriorityWork()
 {
-    return false;
+    return !m_pendingInputTasks.isEmpty() || !m_pendingCompositorTasks.isEmpty();
+}
+
+void Scheduler::TracedTask::run()
+{
+    TRACE_EVENT2("blink", "TracedTask::run",
+        "src_file", m_location.fileName(),
+        "src_func", m_location.functionName());
+    m_task();
 }
 
 } // namespace blink