Nika Layzell
4e62656d98
This patch introduces a new static helper, StaticBackgroundTaskQueue, which provides a threadsafe static, usable for NS_CreateBackgroundTaskQueue, which will be cleared to nullptr when the background task queue is killed during XPCOM shutdown. This approach may also be extensible in the future to virtual thread pools, potentially replacing SharedThreadPool for some use-cases. Differential Revision: https://phabricator.services.mozilla.com/D273517
68 lines
2.2 KiB
C++
68 lines
2.2 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_StaticBackgroundTaskQueue_h
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#define mozilla_StaticBackgroundTaskQueue_h
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#include "mozilla/Attributes.h"
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#include "mozilla/Mutex.h"
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#include "mozilla/NeverDestroyed.h"
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#include "mozilla/StaticString.h"
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#include "nsCOMPtr.h"
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#include "nsITargetShutdownTask.h"
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namespace mozilla {
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/**
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* Helper class for declaring a process-lifetime shared background task queue in
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* a thread-safe manner.
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*
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* This type is intended to be used as a static-local class, and will construct
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* the task queue when first accessed. The queue will automatically be cleaned
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* up during XPCOM shutdown, after which point Get() will return nullptr.
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*
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* This queue will run on the generic background task queue, and is created
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* using NS_CreateBackgroundTaskQueue.
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*
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* Example Usage:
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*
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* static already_AddRefed<nsISerialEventTarget> FooBarQueue() {
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* static StaticBackgroundTaskQueue sQueue("FooBar");
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* return sQueue.Get();
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* }
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*/
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class MOZ_STATIC_LOCAL_CLASS StaticBackgroundTaskQueue final {
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public:
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explicit StaticBackgroundTaskQueue(StaticString aName);
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already_AddRefed<nsISerialEventTarget> Get();
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private:
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// Inner Impl type. This is wrapped in NeverDestroyed<...> to avoid
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// introducing static destructors, and uses fake refcounting for the
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// nsITargetShutdownTask implementation.
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struct Impl final : public nsITargetShutdownTask {
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explicit Impl(StaticString aName);
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// nsISupports (fake refcounting, always static)
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NS_IMETHOD QueryInterface(REFNSIID aIID, void** aInstancePtr) override;
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NS_IMETHOD_(MozExternalRefCountType) AddRef() override { return 2; }
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NS_IMETHOD_(MozExternalRefCountType) Release() override { return 2; }
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// nsITargetShutdownTask
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void TargetShutdown() override;
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OffTheBooksMutex mMutex;
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nsCOMPtr<nsISerialEventTarget> mQueue MOZ_GUARDED_BY(mMutex);
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};
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NeverDestroyed<Impl> mImpl;
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};
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} // namespace mozilla
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#endif // mozilla_StaticBackgroundTaskQueue_h
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