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       1             : /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
       2             : /* vim: set ts=8 sts=2 et sw=2 tw=80: */
       3             : /* This Source Code Form is subject to the terms of the Mozilla Public
       4             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       5             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       6             : 
       7             : #ifndef nsThreadSyncDispatch_h_
       8             : #define nsThreadSyncDispatch_h_
       9             : 
      10             : #include "mozilla/Atomics.h"
      11             : #include "mozilla/DebugOnly.h"
      12             : 
      13             : #include "nsThreadUtils.h"
      14             : #include "LeakRefPtr.h"
      15             : 
      16           0 : class nsThreadSyncDispatch : public mozilla::Runnable
      17             : {
      18             : public:
      19           0 :   nsThreadSyncDispatch(nsIThread* aOrigin, already_AddRefed<nsIRunnable>&& aTask)
      20           0 :     : Runnable("nsThreadSyncDispatch")
      21             :     , mOrigin(aOrigin)
      22           0 :     , mSyncTask(mozilla::Move(aTask))
      23           0 :     , mIsPending(true)
      24             :   {
      25           0 :   }
      26             : 
      27           0 :   bool IsPending()
      28             :   {
      29             :     // This is an atomic acquire on the origin thread.
      30           0 :     return mIsPending;
      31             :   }
      32             : 
      33             : private:
      34           0 :   NS_IMETHOD Run() override
      35             :   {
      36           0 :     if (nsCOMPtr<nsIRunnable> task = mSyncTask.take()) {
      37           0 :       MOZ_ASSERT(!mSyncTask);
      38             : 
      39           0 :       mozilla::DebugOnly<nsresult> result = task->Run();
      40           0 :       MOZ_ASSERT(NS_SUCCEEDED(result),
      41             :                  "task in sync dispatch should not fail");
      42             : 
      43             :       // We must release the task here to ensure that when the original
      44             :       // thread is unblocked, this task has been released.
      45           0 :       task = nullptr;
      46             : 
      47             :       // This is an atomic release on the target thread.
      48           0 :       mIsPending = false;
      49             : 
      50             :       // unblock the origin thread
      51           0 :       mOrigin->Dispatch(this, NS_DISPATCH_NORMAL);
      52             :     }
      53             : 
      54           0 :     return NS_OK;
      55             :   }
      56             : 
      57             :   nsCOMPtr<nsIThread> mOrigin;
      58             :   // The task is leaked by default when Run() is not called, because
      59             :   // otherwise we may release it in an incorrect thread.
      60             :   mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
      61             :   mozilla::Atomic<bool, mozilla::ReleaseAcquire> mIsPending;
      62             : };
      63             : 
      64             : #endif // nsThreadSyncDispatch_h_