xpcom/threads/nsThreadSyncDispatch.h

   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 class nsThreadSyncDispatch : public mozilla::Runnable {
  17  public:
  18   nsThreadSyncDispatch(already_AddRefed<nsIEventTarget> aOrigin,
  19                        already_AddRefed<nsIRunnable>&& aTask)
  20       : Runnable("nsThreadSyncDispatch"),
  21         mOrigin(aOrigin),
  22         mSyncTask(std::move(aTask)),
  23         mIsPending(true) {}
  24
  25   bool IsPending() {
  26     // This is an atomic acquire on the origin thread.
  27     return mIsPending;
  28   }
  29
  30  private:
  31   NS_IMETHOD Run() override {
  32     if (nsCOMPtr<nsIRunnable> task = mSyncTask.take()) {
  33       MOZ_ASSERT(!mSyncTask);
  34
  35       mozilla::DebugOnly<nsresult> result = task->Run();
  36       MOZ_ASSERT(NS_SUCCEEDED(result), "task in sync dispatch should not fail");
  37
  38       // We must release the task here to ensure that when the original
  39       // thread is unblocked, this task has been released.
  40       task = nullptr;
  41
  42       // This is an atomic release on the target thread.
  43       mIsPending = false;
  44
  45       // unblock the origin thread
  46       mOrigin->Dispatch(this, NS_DISPATCH_NORMAL);
  47     }
  48
  49     return NS_OK;
  50   }
  51
  52   nsCOMPtr<nsIEventTarget> mOrigin;
  53   // The task is leaked by default when Run() is not called, because
  54   // otherwise we may release it in an incorrect thread.
  55   mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
  56   mozilla::Atomic<bool, mozilla::ReleaseAcquire> mIsPending;
  57 };
  58
  59 #endif  // nsThreadSyncDispatch_h_