Introduce a basic Blink Scheduler

Source/platform/scheduler/Scheduler.h

+/*
+ * Copyright (C) 2014 Google Inc. All rights reserved.

[eseidel, 2014/07/15 15:59:11]

Please use the updated 2-line license. instead of this giant blob. :)

[Sami, 2014/07/15 19:20:05]

Ah, somehow I thought that was only for Chromium code but thanks for correcting
me.

+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. 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 INC. 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.
+ */
+
+#ifndef Scheduler_h
+#define Scheduler_h
+
+#include "platform/PlatformExport.h"
+#include "public/platform/WebThread.h"
+#include "wtf/Functional.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/ThreadingPrimitives.h"
+#include <deque>
+
+namespace WebCore {
+
+// The scheduler is an opinionated gateway for arranging work to be run 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 {
+    WTF_MAKE_NONCOPYABLE(Scheduler);
+public:
+    typedef Function<void()> Task;
+
+    static Scheduler* current();
+    static void initializeOnMainThread();
+    static void shutdown();
+
+    // The following entrypoints are used to schedule different types of tasks
+    // to be run on the main thread. They can be called from any thread.
+    void postInputTask(const Task&);
+    void postCompositorTask(const Task&);
+    void postTask(const Task&); // For generic (low priority) tasks.
+
+    // Returns true if there is high priority work pending on the main thread
+    // and the caller should yield to let the scheduler service that work.
+    // Can be called on the main thread.
+    bool shouldYieldForHighPriorityWork();
+
+    // The shared timer can be used to schedule a periodic callback which may
+    // get preempted by higher priority work.
+    void setSharedTimerFiredFunction(void (*function)());
+    void setSharedTimerFireInterval(double);
+    void stopSharedTimer();
+
+private:
+    Scheduler();
+    ~Scheduler();
+
+    void scheduleTask(const Task&);
+
+    static void sharedTimerAdapter();
+    void tickSharedTimer();
+
+    static Scheduler* s_currentScheduler;
+    blink::WebThread* m_mainThread;
+
+    void (*m_sharedTimerFunction)();
+};
+
+} // namespace WebCore
+
+#endif // Scheduler_h