gecko-dev/xpcom/threads/AbstractThread.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/. */
#if !defined(AbstractThread_h_)
#define AbstractThread_h_
#include "mozilla/RefPtr.h"
#include "mozilla/ThreadLocal.h"
#include "nscore.h"
#include "nsIRunnable.h"
#include "nsISerialEventTarget.h"
#include "nsISupportsImpl.h"
#include "nsIThread.h"
namespace mozilla {
class TaskQueue;
class TaskDispatcher;
/*
* NOTE: PLEASE AVOID USE OF AbstractThread OUTSIDE MEDIA CODE WHEN POSSIBLE.
* The nsISerialEventTarget interface should be preferred. AbstractThread
* has unusual "tail dispatch" semantics that usually are not needed outside
* of media code.
*
* 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 DocGroup::AbstractThreadFor().
* If you add support for another thread that is not the MainThread, you'll need
* to figure out how to make it unique such that comparing AbstractThread
* pointers is equivalent to comparing nsIThread pointers.
*/
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) {}
// Returns an AbstractThread wrapper of a nsIThread.
static already_AddRefed<AbstractThread>
CreateXPCOMThreadWrapper(nsIThread* aThread, bool aRequireTailDispatch);
// Returns an AbstractThread wrapper of a non-nsIThread EventTarget on the main thread.
static already_AddRefed<AbstractThread>
CreateEventTargetWrapper(nsIEventTarget* aEventTarget, bool aRequireTailDispatch);
NS_DECL_THREADSAFE_ISUPPORTS
// 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.
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 DispatchFailureHandling { AssertDispatchSuccess, DontAssertDispatchSuccess };
enum DispatchReason { NormalDispatch, TailDispatch };
virtual void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
DispatchFailureHandling aHandling = AssertDispatchSuccess,
DispatchReason aReason = NormalDispatch) = 0;
virtual bool IsCurrentThreadIn() = 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; }
// Helper functions for methods on the tail TasklDispatcher. These check
// HasTailTasks to avoid allocating a TailDispatcher if it isn't
// needed.
void 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 TaskQueue* AsTaskQueue() { MOZ_CRASH("Not a task queue!"); }
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();
void DispatchStateChange(already_AddRefed<nsIRunnable> aRunnable);
static void DispatchDirectTask(already_AddRefed<nsIRunnable> aRunnable);
// Create a runnable that will run |aRunnable| and drain the direct tasks
// generated by it.
virtual already_AddRefed<nsIRunnable>
CreateDirectTaskDrainer(already_AddRefed<nsIRunnable> aRunnable)
{
MOZ_CRASH("Not support!");
}
struct AutoEnter
{
explicit AutoEnter(AbstractThread* aThread)
{
mLastCurrentThread = sCurrentThreadTLS.get();
sCurrentThreadTLS.set(aThread);
}
~AutoEnter()
{
sCurrentThreadTLS.set(mLastCurrentThread);
}
private:
AbstractThread* mLastCurrentThread = nullptr;
};
protected:
virtual ~AbstractThread() {}
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