cc/scoped_thread_proxy.h

   1 // Copyright 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef CCScopedThreadProxy_h
   6 #define CCScopedThreadProxy_h
   7
   8 #include "CCThreadTask.h"
   9 #include "base/threading/platform_thread.h"
  10 #include <wtf/OwnPtr.h>
  11 #include <wtf/PassOwnPtr.h>
  12 #include <wtf/ThreadSafeRefCounted.h>
  13
  14 namespace cc {
  15
  16 // This class is a proxy used to post tasks to an target thread from any other thread. The proxy may be shut down at
  17 // any point from the target thread after which no more tasks posted to the proxy will run. In other words, all
  18 // tasks posted via a proxy are scoped to the lifecycle of the proxy. Use this when posting tasks to an object that
  19 // might die with tasks in flight.
  20 //
  21 // The proxy must be created and shut down from the target thread, tasks may be posted from any thread.
  22 //
  23 // Implementation note: Unlike ScopedRunnableMethodFactory in Chromium, pending tasks are not cancelled by actually
  24 // destroying the proxy. Instead each pending task holds a reference to the proxy to avoid maintaining an explicit
  25 // list of outstanding tasks.
  26 class CCScopedThreadProxy : public ThreadSafeRefCounted<CCScopedThreadProxy> {
  27 public:
  28     static PassRefPtr<CCScopedThreadProxy> create(CCThread* targetThread)
  29     {
  30         ASSERT(base::PlatformThread::CurrentId() == targetThread->threadID());
  31         return adoptRef(new CCScopedThreadProxy(targetThread));
  32     }
  33
  34     ~CCScopedThreadProxy();
  35
  36     // Can be called from any thread. Posts a task to the target thread that runs unless
  37     // shutdown() is called before it runs.
  38     void postTask(PassOwnPtr<CCThread::Task> task)
  39     {
  40         ref();
  41         m_targetThread->postTask(createCCThreadTask(this, &CCScopedThreadProxy::runTaskIfNotShutdown, task));
  42     }
  43
  44     void shutdown()
  45     {
  46         ASSERT(base::PlatformThread::CurrentId() == m_targetThread->threadID());
  47         ASSERT(!m_shutdown);
  48         m_shutdown = true;
  49     }
  50
  51 private:
  52     explicit CCScopedThreadProxy(CCThread* targetThread);
  53
  54     void runTaskIfNotShutdown(PassOwnPtr<CCThread::Task> popTask)
  55     {
  56         OwnPtr<CCThread::Task> task = popTask;
  57         // If our shutdown flag is set, it's possible that m_targetThread has already been destroyed so don't
  58         // touch it.
  59         if (m_shutdown) {
  60             deref();
  61             return;
  62         }
  63         ASSERT(base::PlatformThread::CurrentId() == m_targetThread->threadID());
  64         task->performTask();
  65         deref();
  66     }
  67
  68     CCThread* m_targetThread;
  69     bool m_shutdown; // Only accessed on the target thread
  70 };
  71
  72 }
  73
  74 #endif