[Blink-WebWorkers] WorkerSharedTimer cancels extra delayed tasks.

Source/core/workers/WorkerThread.cpp

 /*
  * Copyright (C) 2008 Apple 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
@@ skipping 67 matching lines @@
     DEFINE_STATIC_LOCAL(HashSet<WorkerThread*>, threads, ());
     return threads;
 }
 
 unsigned WorkerThread::workerThreadCount()
 {
     MutexLocker lock(threadSetMutex());
     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)();
     virtual void setFiredFunction(SharedTimerFunction func)
     {
         m_sharedTimerFunction = func;
         if (!m_sharedTimerFunction)
             m_nextFireTime = 0.0;
     }
 
     virtual void setFireInterval(double interval)

[jochen (gone - plz use gerrit), 2014/09/16 14:17:04]

assume the following two calls happen:

setFireInterval(100);
setFireInterval(200);

we the won't schedule a new task, however, the existing task is still scheduled
for in 100ms. What's missing is to make the existing task do another
postDelayedTask with the remaining delta.

See e.g.
https://code.google.com/p/chromium/codesearch#chromium/src/base/timer/timer.c...
for what the main thread does

     {
         ASSERT(m_sharedTimerFunction);
 
         // See BlinkPlatformImpl::setSharedTimerFireInterval for explanation of
         // why ceil is used in the interval calculation.
         int64 delay = static_cast<int64>(ceil(interval * 1000));
 
         if (delay < 0) {
             delay = 0;
             m_nextFireTime = 0.0;
         }
 
         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 (interval < m_lastQueuedTaskTimer->nextFireInterval()) {
+                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;
+        m_lastQueuedTask = 0;
+        m_lastQueuedTaskTimer = 0;
     }
 
     double nextFireTime() { return m_nextFireTime; }
 
 private:
     void OnTimeout()
     {
         ASSERT(m_workerThread->workerGlobalScope());
+
+        m_lastQueuedTask = 0;
+        m_lastQueuedTaskTimer = 0;
+
         if (m_sharedTimerFunction && m_running && !m_workerThread->workerGlobalScope()->isClosing())
             m_sharedTimerFunction();
     }
 
     WorkerThread* m_workerThread;
     SharedTimerFunction m_sharedTimerFunction;
     double m_nextFireTime;
     bool m_running;
+    WorkerThreadCancelableTask* m_lastQueuedTask;
+    TimerBase* m_lastQueuedTaskTimer;
 };
 
 class WorkerThreadTask : public blink::WebThread::Task {
     WTF_MAKE_NONCOPYABLE(WorkerThreadTask); WTF_MAKE_FAST_ALLOCATED;
 public:
     static PassOwnPtr<WorkerThreadTask> create(const WorkerThread& workerThread, PassOwnPtr<ExecutionContextTask> task, bool isInstrumented)
     {
         return adoptPtr(new WorkerThreadTask(workerThread, task, isInstrumented));
     }
 
@@ skipping 345 matching lines @@
     InspectorInstrumentation::didLeaveNestedRunLoop(m_workerGlobalScope.get());
 }
 
 void WorkerThread::setWorkerInspectorController(WorkerInspectorController* workerInspectorController)
 {
     MutexLocker locker(m_workerInspectorControllerMutex);
     m_workerInspectorController = workerInspectorController;
 }
 
 } // namespace blink