From 36d22d82aa202bb199967e9512281e9a53db42c9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 21:33:14 +0200 Subject: Adding upstream version 115.7.0esr. Signed-off-by: Daniel Baumann --- xpcom/threads/TaskQueue.h | 281 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 281 insertions(+) create mode 100644 xpcom/threads/TaskQueue.h (limited to 'xpcom/threads/TaskQueue.h') diff --git a/xpcom/threads/TaskQueue.h b/xpcom/threads/TaskQueue.h new file mode 100644 index 0000000000..b9321866a9 --- /dev/null +++ b/xpcom/threads/TaskQueue.h @@ -0,0 +1,281 @@ +/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ +/* vim: set ts=8 sts=2 et sw=2 tw=80: */ +/* This Source Code Form is subject to the terms of the Mozilla Public + * License, v. 2.0. If a copy of the MPL was not distributed with this + * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ + +#ifndef TaskQueue_h_ +#define TaskQueue_h_ + +#include "mozilla/AbstractThread.h" +#include "mozilla/Maybe.h" +#include "mozilla/Monitor.h" +#include "mozilla/MozPromise.h" +#include "mozilla/Queue.h" +#include "mozilla/RefPtr.h" +#include "mozilla/TaskDispatcher.h" +#include "mozilla/ThreadSafeWeakPtr.h" +#include "nsIDirectTaskDispatcher.h" +#include "nsThreadUtils.h" + +namespace mozilla { + +typedef MozPromise ShutdownPromise; + +class TaskQueueTrackerEntry; + +// Abstracts executing runnables in order on an arbitrary event target. The +// runnables dispatched to the TaskQueue will be executed in the order in which +// they're received, and are guaranteed to not be executed concurrently. +// They may be executed on different threads, and a memory barrier is used +// to make this threadsafe for objects that aren't already threadsafe. +// +// Note, since a TaskQueue can also be converted to an nsIEventTarget using +// WrapAsEventTarget() its possible to construct a hierarchy of TaskQueues. +// Consider these three TaskQueues: +// +// TQ1 dispatches to the main thread +// TQ2 dispatches to TQ1 +// TQ3 dispatches to TQ1 +// +// This ensures there is only ever a single runnable from the entire chain on +// the main thread. It also ensures that TQ2 and TQ3 only have a single +// runnable in TQ1 at any time. +// +// This arrangement lets you prioritize work by dispatching runnables directly +// to TQ1. You can issue many runnables for important work. Meanwhile the TQ2 +// and TQ3 work will always execute at most one runnable and then yield. +// +// A TaskQueue does not require explicit shutdown, however it provides a +// BeginShutdown() method that places TaskQueue in a shut down state and returns +// a promise that gets resolved once all pending tasks have completed +class TaskQueue final : public AbstractThread, + public nsIDirectTaskDispatcher, + public SupportsThreadSafeWeakPtr { + class EventTargetWrapper; + + public: + NS_DECL_ISUPPORTS_INHERITED + NS_DECL_NSIDIRECTTASKDISPATCHER + MOZ_DECLARE_REFCOUNTED_TYPENAME(TaskQueue) + + static RefPtr Create(already_AddRefed aTarget, + const char* aName, + bool aSupportsTailDispatch = false); + + TaskDispatcher& TailDispatcher() override; + + NS_IMETHOD Dispatch(already_AddRefed aEvent, + uint32_t aFlags) override { + nsCOMPtr runnable = aEvent; + { + MonitorAutoLock mon(mQueueMonitor); + return DispatchLocked(/* passed by ref */ runnable, aFlags, + NormalDispatch); + } + // If the ownership of |r| is not transferred in DispatchLocked() due to + // dispatch failure, it will be deleted here outside the lock. We do so + // since the destructor of the runnable might access TaskQueue and result + // in deadlocks. + } + + [[nodiscard]] nsresult Dispatch( + already_AddRefed aRunnable, + DispatchReason aReason = NormalDispatch) override { + nsCOMPtr r = aRunnable; + { + MonitorAutoLock mon(mQueueMonitor); + return DispatchLocked(/* passed by ref */ r, NS_DISPATCH_NORMAL, aReason); + } + // If the ownership of |r| is not transferred in DispatchLocked() due to + // dispatch failure, it will be deleted here outside the lock. We do so + // since the destructor of the runnable might access TaskQueue and result + // in deadlocks. + } + + // So we can access nsIEventTarget::Dispatch(nsIRunnable*, uint32_t aFlags) + using nsIEventTarget::Dispatch; + + NS_IMETHOD RegisterShutdownTask(nsITargetShutdownTask* aTask) override; + NS_IMETHOD UnregisterShutdownTask(nsITargetShutdownTask* aTask) override; + + using CancelPromise = MozPromise; + + // Dispatches a task to cancel any pending DelayedRunnables. Idempotent. Only + // dispatches the task on the first call. Creating DelayedRunnables after this + // is called will result in assertion failures. + RefPtr CancelDelayedRunnables(); + + // Puts the queue in a shutdown state and returns immediately. The queue will + // remain alive at least until all the events are drained, because the Runners + // hold a strong reference to the task queue, and one of them is always held + // by the target event queue when the task queue is non-empty. + // + // The returned promise is resolved when the queue goes empty. + RefPtr BeginShutdown(); + + // Blocks until all task finish executing. + void AwaitIdle(); + + // Blocks until the queue is flagged for shutdown and all tasks have finished + // executing. + void AwaitShutdownAndIdle(); + + bool IsEmpty(); + + // Returns true if the current thread is currently running a Runnable in + // the task queue. + bool IsCurrentThreadIn() const override; + using nsISerialEventTarget::IsOnCurrentThread; + + private: + friend class SupportsThreadSafeWeakPtr; + + TaskQueue(already_AddRefed aTarget, const char* aName, + bool aSupportsTailDispatch); + + virtual ~TaskQueue(); + + // Blocks until all task finish executing. Called internally by methods + // that need to wait until the task queue is idle. + // mQueueMonitor must be held. + void AwaitIdleLocked(); + + nsresult DispatchLocked(nsCOMPtr& aRunnable, uint32_t aFlags, + DispatchReason aReason = NormalDispatch); + + void MaybeResolveShutdown(); + + nsCOMPtr mTarget MOZ_GUARDED_BY(mQueueMonitor); + + // Handle for this TaskQueue being registered with our target if it implements + // TaskQueueTracker. + UniquePtr mTrackerEntry MOZ_GUARDED_BY(mQueueMonitor); + + // Monitor that protects the queue, mIsRunning, mIsShutdown and + // mShutdownTasks; + Monitor mQueueMonitor; + + typedef struct TaskStruct { + nsCOMPtr event; + uint32_t flags; + } TaskStruct; + + // Queue of tasks to run. + Queue mTasks MOZ_GUARDED_BY(mQueueMonitor); + + // List of tasks to run during shutdown. + nsTArray> mShutdownTasks + MOZ_GUARDED_BY(mQueueMonitor); + + // The thread currently running the task queue. We store a reference + // to this so that IsCurrentThreadIn() can tell if the current thread + // is the thread currently running in the task queue. + // + // This may be read on any thread, but may only be written on mRunningThread. + // The thread can't die while we're running in it, and we only use it for + // pointer-comparison with the current thread anyway - so we make it atomic + // and don't refcount it. + Atomic mRunningThread; + + // RAII class that gets instantiated for each dispatched task. + class AutoTaskGuard { + public: + explicit AutoTaskGuard(TaskQueue* aQueue) + : mQueue(aQueue), mLastCurrentThread(nullptr) { + // NB: We don't hold the lock to aQueue here. Don't do anything that + // might require it. + MOZ_ASSERT(!mQueue->mTailDispatcher); + mTaskDispatcher.emplace(aQueue, + /* aIsTailDispatcher = */ true); + mQueue->mTailDispatcher = mTaskDispatcher.ptr(); + + mLastCurrentThread = sCurrentThreadTLS.get(); + sCurrentThreadTLS.set(aQueue); + + MOZ_ASSERT(mQueue->mRunningThread == nullptr); + mQueue->mRunningThread = PR_GetCurrentThread(); + } + + ~AutoTaskGuard() { + mTaskDispatcher->DrainDirectTasks(); + mTaskDispatcher.reset(); + + MOZ_ASSERT(mQueue->mRunningThread == PR_GetCurrentThread()); + mQueue->mRunningThread = nullptr; + + sCurrentThreadTLS.set(mLastCurrentThread); + mQueue->mTailDispatcher = nullptr; + } + + private: + Maybe mTaskDispatcher; + TaskQueue* mQueue; + AbstractThread* mLastCurrentThread; + }; + + TaskDispatcher* mTailDispatcher; + + // True if we've dispatched an event to the target to execute events from + // the queue. + bool mIsRunning MOZ_GUARDED_BY(mQueueMonitor); + + // True if we've started our shutdown process. + bool mIsShutdown MOZ_GUARDED_BY(mQueueMonitor); + MozPromiseHolder mShutdownPromise + MOZ_GUARDED_BY(mQueueMonitor); + + // The name of this TaskQueue. Useful when debugging dispatch failures. + const char* const mName; + + SimpleTaskQueue mDirectTasks; + + class Runner : public Runnable { + public: + explicit Runner(TaskQueue* aQueue) + : Runnable("TaskQueue::Runner"), mQueue(aQueue) {} + NS_IMETHOD Run() override; + + private: + RefPtr mQueue; + }; +}; + +#define MOZILLA_TASKQUEUETRACKER_IID \ + { \ + 0x765c4b56, 0xd5f6, 0x4a9f, { \ + 0x91, 0xcf, 0x51, 0x47, 0xb3, 0xc1, 0x7e, 0xa6 \ + } \ + } + +// XPCOM "interface" which may be implemented by nsIEventTarget implementations +// which want to keep track of what TaskQueue instances are currently targeting +// them. This may be used to asynchronously shutdown TaskQueues targeting a +// threadpool or other event target before the threadpool goes away. +// +// This explicitly TaskQueue-aware tracker is used instead of +// `nsITargetShutdownTask` as the operations required to shut down a TaskQueue +// are asynchronous, which is not a requirement of that interface. +class TaskQueueTracker : public nsISupports { + public: + NS_DECLARE_STATIC_IID_ACCESSOR(MOZILLA_TASKQUEUETRACKER_IID) + + // Get a strong reference to every TaskQueue currently tracked by this + // TaskQueueTracker. May be called from any thraed. + nsTArray> GetAllTrackedTaskQueues(); + + protected: + virtual ~TaskQueueTracker(); + + private: + friend class TaskQueueTrackerEntry; + + Mutex mMutex{"TaskQueueTracker"}; + LinkedList mEntries MOZ_GUARDED_BY(mMutex); +}; + +NS_DEFINE_STATIC_IID_ACCESSOR(TaskQueueTracker, MOZILLA_TASKQUEUETRACKER_IID) + +} // namespace mozilla + +#endif // TaskQueue_h_ -- cgit v1.2.3