dom/quota/ThreadUtils.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 DOM_QUOTA_THREADUTILS_H_
   8 #define DOM_QUOTA_THREADUTILS_H_
   9
  10 #include <cstdint>
  11 #include <functional>
  12
  13 #include "mozilla/StaticPrefsBase.h"
  14
  15 enum class nsresult : uint32_t;
  16
  17 namespace mozilla::dom::quota {
  18
  19 /**
  20  * Add a temporary thread observer and listen for the "AfterProcessNextEvent"
  21  * notification. Once the notification is received, remove the temporary thread
  22  * observer and call aCallback.
  23  * In practice, this calls aCallback immediately after the current thread is
  24  * done with running and releasing recently popped event from thread's event
  25  * queue.
  26  * If called multiple times, all the callbacks will be executed, in the
  27  * order in which RunAfterProcessingCurrentEvent() was called.
  28  * Use this method if you need to dispatch the same or some other runnable to
  29  * another thread in a way which prevents any race conditions (for example
  30  * unpredictable releases of objects).
  31  * This method should be used only in existing code which can't be easily
  32  * converted to use MozPromise which doesn't have the problem with
  33  * unpredictable releases of objects, see:
  34  * https://searchfox.org/mozilla-central/rev/4582d908c17fbf7924f5699609fe4a12c28ddc4a/xpcom/threads/MozPromise.h#866
  35  *
  36  * Note: Calling this method from a thread pool is not supported since thread
  37  * pools don't fire the "AfterProcessNextEvent" notification. The method has
  38  * a diagnostic assertion for that so any calls like that will be caught
  39  * in builds with enabled diagnostic assertions. The callback will never
  40  * get executed in other builds, such as release builds. The limitation can
  41  * be removed completely when thread pool implementation gets support for firing
  42  * the "AfterProcessNextEvent".
  43  */
  44 nsresult RunAfterProcessingCurrentEvent(std::function<void()>&& aCallback);
  45
  46 /**
  47  * Causes the current thread to yield for a specified amount of milliseconds if
  48  * a mirrored preference value is not zero.
  49  *
  50  * @param aMirroredPrefValue
  51  *   A mirrored preference value. If this value is greater than zero, the
  52  *   function will cause the current thread to sleep for that number of
  53  *   milliseconds.
  54  */
  55 void SleepIfEnabled(StripAtomic<RelaxedAtomicUint32> aMirroredPrefValue);
  56
  57 }  // namespace mozilla::dom::quota
  58
  59 #endif  // DOM_QUOTA_THREADUTILS_H_