зеркало из https://github.com/mozilla/gecko-dev.git
132 строки
5.2 KiB
C++
132 строки
5.2 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
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#if !defined(AbstractThread_h_)
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# define AbstractThread_h_
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# include "mozilla/AlreadyAddRefed.h"
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# include "mozilla/ThreadLocal.h"
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# include "nscore.h"
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# include "nsISerialEventTarget.h"
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# include "nsISupports.h"
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class nsIEventTarget;
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class nsIRunnable;
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class nsIThread;
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namespace mozilla {
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class TaskDispatcher;
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/*
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* We often want to run tasks on a target that guarantees that events will never
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* run in parallel. There are various target types that achieve this - namely
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* nsIThread and TaskQueue. Note that nsIThreadPool (which implements
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* nsIEventTarget) does not have this property, so we do not want to use
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* nsIEventTarget for this purpose. This class encapsulates the specifics of
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* the structures we might use here and provides a consistent interface.
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*
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* At present, the supported AbstractThread implementations are TaskQueue,
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* AbstractThread::MainThread() and XPCOMThreadWrapper which can wrap any
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* nsThread.
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*
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* The primary use of XPCOMThreadWrapper is to allow any threads to provide
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* Direct Task dispatching which is similar (but not identical to) the microtask
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* semantics of JS promises. Instantiating a XPCOMThreadWrapper on the current
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* nsThread is sufficient to enable direct task dispatching.
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*
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* You shouldn't use pointers when comparing AbstractThread or nsIThread to
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* determine if you are currently on the thread, but instead use the
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* nsISerialEventTarget::IsOnCurrentThread() method.
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*/
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class AbstractThread : public nsISerialEventTarget {
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public:
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// Returns the AbstractThread that the caller is currently running in, or null
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// if the caller is not running in an AbstractThread.
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static AbstractThread* GetCurrent() { return sCurrentThreadTLS.get(); }
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AbstractThread(bool aSupportsTailDispatch)
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: mSupportsTailDispatch(aSupportsTailDispatch) {}
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NS_DECL_THREADSAFE_ISUPPORTS
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// We don't use NS_DECL_NSIEVENTTARGET so that we can remove the default
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// |flags| parameter from Dispatch. Otherwise, a single-argument Dispatch call
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// would be ambiguous.
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using nsISerialEventTarget::IsOnCurrentThread;
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NS_IMETHOD_(bool) IsOnCurrentThreadInfallible(void) override;
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NS_IMETHOD IsOnCurrentThread(bool* _retval) override;
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NS_IMETHOD Dispatch(already_AddRefed<nsIRunnable> event,
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uint32_t flags) override;
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NS_IMETHOD DispatchFromScript(nsIRunnable* event, uint32_t flags) override;
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NS_IMETHOD DelayedDispatch(already_AddRefed<nsIRunnable> event,
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uint32_t delay) override;
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enum DispatchReason { NormalDispatch, TailDispatch };
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virtual nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable,
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DispatchReason aReason = NormalDispatch) = 0;
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virtual bool IsCurrentThreadIn() const = 0;
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// Returns a TaskDispatcher that will dispatch its tasks when the currently-
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// running tasks pops off the stack.
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//
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// May only be called when running within the it is invoked up, and only on
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// threads which support it.
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virtual TaskDispatcher& TailDispatcher() = 0;
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// Returns true if we have tail tasks scheduled, or if this isn't known.
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// Returns false if we definitely don't have any tail tasks.
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virtual bool MightHaveTailTasks() { return true; }
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// Returns true if the tail dispatcher is available. In certain edge cases
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// like shutdown, it might not be.
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virtual bool IsTailDispatcherAvailable() { return true; }
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// Helper functions for methods on the tail TasklDispatcher. These check
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// HasTailTasks to avoid allocating a TailDispatcher if it isn't
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// needed.
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nsresult TailDispatchTasksFor(AbstractThread* aThread);
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bool HasTailTasksFor(AbstractThread* aThread);
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// Returns true if this supports the tail dispatcher.
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bool SupportsTailDispatch() const { return mSupportsTailDispatch; }
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// Returns true if this thread requires all dispatches originating from
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// aThread go through the tail dispatcher.
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bool RequiresTailDispatch(AbstractThread* aThread) const;
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bool RequiresTailDispatchFromCurrentThread() const;
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virtual nsIEventTarget* AsEventTarget() { MOZ_CRASH("Not an event target!"); }
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// Returns the non-DocGroup version of AbstractThread on the main thread.
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// A DocGroup-versioned one is available in
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// DispatcherTrait::AbstractThreadFor(). Note:
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// DispatcherTrait::AbstractThreadFor() SHALL be used when possible.
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static AbstractThread* MainThread();
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// Must be called exactly once during startup.
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static void InitTLS();
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static void InitMainThread();
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static void ShutdownMainThread();
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void DispatchStateChange(already_AddRefed<nsIRunnable> aRunnable);
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static void DispatchDirectTask(already_AddRefed<nsIRunnable> aRunnable);
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protected:
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virtual ~AbstractThread() = default;
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static MOZ_THREAD_LOCAL(AbstractThread*) sCurrentThreadTLS;
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// True if we want to require that every task dispatched from tasks running in
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// this queue go through our queue's tail dispatcher.
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const bool mSupportsTailDispatch;
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};
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} // namespace mozilla
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#endif
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