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