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 #include "mozilla/SpinEventLoopUntil.h"
  13
  14 #include "nsThreadUtils.h"
  15 #include "LeakRefPtr.h"
  16
  17 class nsThreadSyncDispatch : public mozilla::Runnable {
  18  public:
  19   nsThreadSyncDispatch(already_AddRefed<nsIEventTarget> aOrigin,
  20                        already_AddRefed<nsIRunnable>&& aTask)
  21       : Runnable("nsThreadSyncDispatch"),
  22         mOrigin(aOrigin),
  23         mSyncTask(std::move(aTask)),
  24         mIsPending(true) {}
  25
  26   bool IsPending() {
  27     // This is an atomic acquire on the origin thread.
  28     return mIsPending;
  29   }
  30
  31   void SpinEventLoopUntilComplete(const nsACString& aVeryGoodReasonToDoThis) {
  32     mozilla::SpinEventLoopUntil(aVeryGoodReasonToDoThis,
  33                                 [&]() -> bool { return !IsPending(); });
  34   }
  35
  36  private:
  37   NS_IMETHOD Run() override {
  38     if (nsCOMPtr<nsIRunnable> task = mSyncTask.take()) {
  39       MOZ_ASSERT(!mSyncTask);
  40
  41       mozilla::DebugOnly<nsresult> result = task->Run();
  42       MOZ_ASSERT(NS_SUCCEEDED(result), "task in sync dispatch should not fail");
  43
  44       // We must release the task here to ensure that when the original
  45       // thread is unblocked, this task has been released.
  46       task = nullptr;
  47
  48       // This is an atomic release on the target thread.
  49       mIsPending = false;
  50
  51       // unblock the origin thread
  52       mOrigin->Dispatch(this, NS_DISPATCH_IGNORE_BLOCK_DISPATCH);
  53     }
  54
  55     return NS_OK;
  56   }
  57
  58   nsCOMPtr<nsIEventTarget> mOrigin;
  59   // The task is leaked by default when Run() is not called, because
  60   // otherwise we may release it in an incorrect thread.
  61   mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
  62   mozilla::Atomic<bool, mozilla::ReleaseAcquire> mIsPending;
  63 };
  64
  65 #endif  // nsThreadSyncDispatch_h_