Prioritizing input and compositor tasks in the blink scheduler.

Source/platform/scheduler/DoubleBufferedDeque.h

Index: Source/platform/scheduler/DoubleBufferedDeque.h
diff --git a/Source/platform/scheduler/DoubleBufferedDeque.h b/Source/platform/scheduler/DoubleBufferedDeque.h
new file mode 100644
index 0000000000000000000000000000000000000000..cfae0599a35d763d91019b86cb409bd4a89012db
--- /dev/null
+++ b/Source/platform/scheduler/DoubleBufferedDeque.h
@@ -0,0 +1,44 @@
+#ifndef DoubleBufferedDeque_h

[Sami, 2014/08/08 15:31:13]

Please add a copyright header.

+#define DoubleBufferedDeque_h
+
+#include "wtf/Deque.h"
+#include "wtf/Noncopyable.h"
+#include "wtf/ThreadingPrimitives.h"
+
+namespace blink {
+
+template <typename T> class DoubleBufferedDeque {
+    WTF_MAKE_NONCOPYABLE(DoubleBufferedDeque);
+public:
+    DoubleBufferedDeque()
+        : m_activeIndex(0) { }
+
+    void append(const T& value)
+    {
+        Locker<Mutex> lock(m_mutex);
+        m_queue[m_activeIndex].append(value);
+    }
+
+    bool isEmpty()
+    {
+        Locker<Mutex> lock(m_mutex);
+        return m_queue[m_activeIndex].isEmpty();
+    }
+
+    WTF::Deque<T>& swapBuffers()
+    {
+        Locker<Mutex> lock(m_mutex);

[Sami, 2014/08/08 15:31:13]

Let's DCHECK that the new queue is empty here. If there are any tasks left in
there, we'll get an ordering bug.

[alexclarke, 2014/08/08 15:47:45]

Good idea, although I'll need to change one of the tests slightly because of
this :)

+        int oldIndex = m_activeIndex;
+        m_activeIndex ^= 1;
+        return m_queue[oldIndex];
+    }
+
+private:
+    WTF::Deque<T> m_queue[2];
+    int m_activeIndex;
+    Mutex m_mutex;
+};
+
+} // namespace blink
+
+#endif // DoubleBufferedDeque_h