[Blink-WebWorkers] WorkerSharedTimer cancels extra delayed tasks.

Source/core/workers/WorkerThread.cpp

Index: Source/core/workers/WorkerThread.cpp
diff --git a/Source/core/workers/WorkerThread.cpp b/Source/core/workers/WorkerThread.cpp
index 6b444d379c3e6da148216e69ff8901912ea97fad..14124885b2621042b442757e4bfc4da06e02266e 100644
--- a/Source/core/workers/WorkerThread.cpp
+++ b/Source/core/workers/WorkerThread.cpp
@@ -85,12 +85,40 @@ unsigned WorkerThread::workerThreadCount()
     return workerThreads().size();
 }
 
+class WorkerThreadCancelableTask FINAL : public ExecutionContextTask {
+    WTF_MAKE_NONCOPYABLE(WorkerThreadCancelableTask); WTF_MAKE_FAST_ALLOCATED;
+public:
+    static PassOwnPtr<WorkerThreadCancelableTask> create(const Closure& closure)
+    {
+        return adoptPtr(new WorkerThreadCancelableTask(closure));
+    }
+
+    virtual void performTask(ExecutionContext*) OVERRIDE
+    {
+        if (!m_taskCanceled)
+            m_closure();
+    }
+
+    void cancelTask() { m_taskCanceled = true; }
+
+private:
+    explicit WorkerThreadCancelableTask(const Closure& closure)
+    : m_closure(closure)
+    , m_taskCanceled(false)
+    { }
+
+    Closure m_closure;
+    bool m_taskCanceled;
+};
+
 class WorkerSharedTimer : public SharedTimer {
 public:
     explicit WorkerSharedTimer(WorkerThread* workerThread)
         : m_workerThread(workerThread)
         , m_nextFireTime(0.0)
         , m_running(false)
+        , m_lastQueuedTask(0)
+        , m_lastQueuedTaskTimer(0)
     { }
 
     typedef void (*SharedTimerFunction)();
@@ -116,12 +144,36 @@ public:
 
         m_running = true;
         m_nextFireTime = currentTime() + interval;
-        m_workerThread->postDelayedTask(createSameThreadTask(&WorkerSharedTimer::OnTimeout, this), delay);
+        if (m_lastQueuedTask) {
+            // If something was queued up before this, check if its later than the current timer
+            if (m_lastQueuedTaskTimer->isActive()) {

[jochen (gone - plz use gerrit), 2014/09/19 13:37:09]

ok, if you want to go without posting a task for the time difference, we can
simplify this a bit:

get rid of m_lastQueuedTaskTimer, and just always cancel the currently queued
task

[Mayur Kankanwadi, 2014/09/19 13:53:24]

I am bit confused with this suggestion.
If we discard m_lastQueuedTaskTimer, how would we know if the top of heap timer
interval is greater or less than the currently passed timer interval. As it is
not mandatory that the interval sent across is smaller than that of the
previously queued task.

+                if (interval < m_lastQueuedTaskTimer->nextFireInterval()) {
+                    m_lastQueuedTask->cancelTask();
+                    m_lastQueuedTask = 0;
+                    m_lastQueuedTaskTimer = 0;
+                }
+            } else {
+                m_lastQueuedTask->cancelTask();
+                m_lastQueuedTask = 0;
+                m_lastQueuedTaskTimer = 0;
+            }
+        }
+        if (!m_lastQueuedTask) {
+            // Now queue the task as a cancellable one.
+            m_lastQueuedTask = WorkerThreadCancelableTask::create(bind(&WorkerSharedTimer::OnTimeout, this)).leakPtr();
+            m_workerThread->postDelayedTask(adoptPtr(m_lastQueuedTask), delay);
+            // The current timer should ideally be at the top of the heap as its assumed to be the smallest interval in the heap
+            m_lastQueuedTaskTimer = PlatformThreadData::current().threadTimers().timerHeap().first();
+        }
     }
 
     virtual void stop()
     {
         m_running = false;
+        if (m_lastQueuedTask)
+            m_lastQueuedTask->cancelTask();
+        m_lastQueuedTask = 0;
+        m_lastQueuedTaskTimer = 0;
     }
 
     double nextFireTime() { return m_nextFireTime; }
@@ -130,6 +182,10 @@ private:
     void OnTimeout()
     {
         ASSERT(m_workerThread->workerGlobalScope());
+
+        m_lastQueuedTask = 0;
+        m_lastQueuedTaskTimer = 0;
+
         if (m_sharedTimerFunction && m_running && !m_workerThread->workerGlobalScope()->isClosing())
             m_sharedTimerFunction();
     }
@@ -138,6 +194,8 @@ private:
     SharedTimerFunction m_sharedTimerFunction;
     double m_nextFireTime;
     bool m_running;
+    WorkerThreadCancelableTask* m_lastQueuedTask;
+    TimerBase* m_lastQueuedTaskTimer;
 };
 
 class WorkerThreadTask : public blink::WebThread::Task {