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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 01:47:29 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-19 01:47:29 +0000
commit0ebf5bdf043a27fd3dfb7f92e0cb63d88954c44d (patch)
treea31f07c9bcca9d56ce61e9a1ffd30ef350d513aa /xpcom/threads/TaskQueue.h
parentInitial commit. (diff)
downloadfirefox-esr-upstream/115.8.0esr.tar.xz
firefox-esr-upstream/115.8.0esr.zip
Adding upstream version 115.8.0esr.upstream/115.8.0esr
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'xpcom/threads/TaskQueue.h')
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1 files changed, 281 insertions, 0 deletions
diff --git a/xpcom/threads/TaskQueue.h b/xpcom/threads/TaskQueue.h
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+/* -*- 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<bool, bool, false> 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<TaskQueue> {
+ class EventTargetWrapper;
+
+ public:
+ NS_DECL_ISUPPORTS_INHERITED
+ NS_DECL_NSIDIRECTTASKDISPATCHER
+ MOZ_DECLARE_REFCOUNTED_TYPENAME(TaskQueue)
+
+ static RefPtr<TaskQueue> Create(already_AddRefed<nsIEventTarget> aTarget,
+ const char* aName,
+ bool aSupportsTailDispatch = false);
+
+ TaskDispatcher& TailDispatcher() override;
+
+ NS_IMETHOD Dispatch(already_AddRefed<nsIRunnable> aEvent,
+ uint32_t aFlags) override {
+ nsCOMPtr<nsIRunnable> 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<nsIRunnable> aRunnable,
+ DispatchReason aReason = NormalDispatch) override {
+ nsCOMPtr<nsIRunnable> 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<bool, bool, false>;
+
+ // 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<CancelPromise> 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<ShutdownPromise> 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>;
+
+ TaskQueue(already_AddRefed<nsIEventTarget> 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<nsIRunnable>& aRunnable, uint32_t aFlags,
+ DispatchReason aReason = NormalDispatch);
+
+ void MaybeResolveShutdown();
+
+ nsCOMPtr<nsIEventTarget> mTarget MOZ_GUARDED_BY(mQueueMonitor);
+
+ // Handle for this TaskQueue being registered with our target if it implements
+ // TaskQueueTracker.
+ UniquePtr<TaskQueueTrackerEntry> mTrackerEntry MOZ_GUARDED_BY(mQueueMonitor);
+
+ // Monitor that protects the queue, mIsRunning, mIsShutdown and
+ // mShutdownTasks;
+ Monitor mQueueMonitor;
+
+ typedef struct TaskStruct {
+ nsCOMPtr<nsIRunnable> event;
+ uint32_t flags;
+ } TaskStruct;
+
+ // Queue of tasks to run.
+ Queue<TaskStruct> mTasks MOZ_GUARDED_BY(mQueueMonitor);
+
+ // List of tasks to run during shutdown.
+ nsTArray<nsCOMPtr<nsITargetShutdownTask>> 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<PRThread*> 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<AutoTaskDispatcher> 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<ShutdownPromise> 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<TaskQueue> 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<RefPtr<TaskQueue>> GetAllTrackedTaskQueues();
+
+ protected:
+ virtual ~TaskQueueTracker();
+
+ private:
+ friend class TaskQueueTrackerEntry;
+
+ Mutex mMutex{"TaskQueueTracker"};
+ LinkedList<TaskQueueTrackerEntry> mEntries MOZ_GUARDED_BY(mMutex);
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(TaskQueueTracker, MOZILLA_TASKQUEUETRACKER_IID)
+
+} // namespace mozilla
+
+#endif // TaskQueue_h_
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