Introduce a basic 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
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+/*
+ * Copyright (C) 2014 Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+ * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "config.h"
+#include "platform/scheduler/Scheduler.h"
+
+#include "platform/Task.h"
+#include "platform/TraceEvent.h"
+#include "public/platform/Platform.h"
+
+namespace WebCore {
+
+Scheduler* Scheduler::s_currentScheduler = 0;
+
+void Scheduler::initializeOnMainThread()
+{
+    s_currentScheduler = new Scheduler();
+}
+
+void Scheduler::shutdown()
+{
+    delete s_currentScheduler;
+    s_currentScheduler = nullptr;
+}
+
+Scheduler* Scheduler::current()
+{
+    return s_currentScheduler;
+}
+
+Scheduler::Scheduler()
+    : m_mainThread(blink::Platform::current()->currentThread())
+    , m_sharedTimerFunction(nullptr)
+    , m_workScheduled(false)
+    , m_hasPendingBeginFrameTask(false)
+{
+}
+
+Scheduler::~Scheduler()
+{
+    runScheduledTasks();
+    ASSERT(!chooseNextTask());
+}
+
+void Scheduler::scheduleTask(TaskQueue* queue, blink::WebThread::Task* task)
+{
+    MutexLocker lock(m_taskQueueLock);
+    queue->push_back(task);
+    if (m_workScheduled)
+        return;
+    m_workScheduled = true;
+    m_mainThread->postTask(new Task(WTF::bind(&Scheduler::runScheduledTasks, this)));
+}
+
+void Scheduler::runScheduledTasks()
+{
+    TRACE_EVENT0("blink", "Scheduler::runScheduledTasks");
+    {
+        MutexLocker lock(m_taskQueueLock);
+        m_workScheduled = false;
+        m_hasPendingBeginFrameTask = false;
+    }
+    while (OwnPtr<blink::WebThread::Task> task = chooseNextTask())
+        task->run();
+}
+
+PassOwnPtr<blink::WebThread::Task> Scheduler::chooseNextTask()
+{
+    MutexLocker lock(m_taskQueueLock);
+    TaskQueue* queues[] = {
+        &m_pendingInputTasks,
+        &m_pendingCompositorTasks,
+        &m_pendingTasks,
+    };
+
+    for (size_t i = 0; i < arraysize(queues); i++) {
+        if (!queues[i]->size())
+            continue;
+        OwnPtr<blink::WebThread::Task> task = adoptPtr(queues[i]->front());
+        queues[i]->pop_front();
+        return task.release();
+    }
+    return nullptr;
+}
+
+void Scheduler::runSharedTimer()
+{
+    TRACE_EVENT0("blink", "Scheduler::runSharedTimer");
+    if (shouldYieldForHighPriorityWork()) {
+        postTask(new Task(WTF::bind(&Scheduler::runSharedTimer, this)));
+        return;
+    }
+    if (m_sharedTimerFunction)
+        m_sharedTimerFunction();
+}
+
+void Scheduler::postTask(blink::WebThread::Task* task)
+{
+    scheduleTask(&m_pendingTasks, task);
+}
+
+void Scheduler::postInputTask(blink::WebThread::Task* task)
+{
+    scheduleTask(&m_pendingInputTasks, task);
+}
+
+void Scheduler::postCompositorTask(blink::WebThread::Task* task)
+{
+    scheduleTask(&m_pendingCompositorTasks, task);
+}
+
+void Scheduler::postBeginFrameTask(blink::WebThread::Task* task, double frameTime, double deadline, double interval)
+{
+    {
+        MutexLocker lock(m_taskQueueLock);
+        m_hasPendingBeginFrameTask = true;
+    }
+    postCompositorTask(task);
+}
+
+void Scheduler::sharedTimerAdapter()
+{
+    current()->runSharedTimer();
+}
+
+void Scheduler::setSharedTimerFiredFunction(void (*function)())
+{
+    m_sharedTimerFunction = function;
+    blink::Platform::current()->setSharedTimerFiredFunction(function ? &Scheduler::sharedTimerAdapter : nullptr);
+}
+
+void Scheduler::setSharedTimerFireInterval(double interval)
+{
+    blink::Platform::current()->setSharedTimerFireInterval(interval);
+}
+
+void Scheduler::stopSharedTimer()
+{
+    blink::Platform::current()->stopSharedTimer();
+}
+
+bool Scheduler::shouldYieldForHighPriorityWork()
+{
+    // TODO: Use atomics.
+    MutexLocker lock(m_taskQueueLock);
+    bool yield = m_pendingInputTasks.size() || m_hasPendingBeginFrameTask;
+    TRACE_EVENT_INSTANT1("blink", "Scheduler::shouldYieldForHighPriorityWork", "yield", yield);
+    return yield;
+}
+
+}