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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 mozilla_SyncRunnable_h
#define mozilla_SyncRunnable_h
#include <utility>
#include "mozilla/AbstractThread.h"
#include "mozilla/Monitor.h"
#include "mozilla/dom/JSExecutionManager.h"
#include "nsThreadUtils.h"
namespace mozilla {
/**
* This class will wrap a nsIRunnable and dispatch it to the target thread
* synchronously. This is different from nsIEventTarget.DISPATCH_SYNC:
* this class does not spin the event loop waiting for the event to be
* dispatched. This means that you don't risk reentrance from pending
* messages, but you must be sure that the target thread does not ever block
* on this thread, or else you will deadlock.
*
* Typical usage:
* RefPtr<SyncRunnable> sr = new SyncRunnable(new myrunnable...());
* sr->DispatchToThread(t);
*
* We also provide convenience wrappers:
* SyncRunnable::DispatchToThread(pThread, new myrunnable...());
* SyncRunnable::DispatchToThread(pThread, NS_NewRunnableFunction(...));
*
*/
class SyncRunnable : public Runnable {
public:
explicit SyncRunnable(nsIRunnable* aRunnable)
: Runnable("SyncRunnable"),
mRunnable(aRunnable),
mMonitor("SyncRunnable"),
mDone(false) {}
explicit SyncRunnable(already_AddRefed<nsIRunnable> aRunnable)
: Runnable("SyncRunnable"),
mRunnable(std::move(aRunnable)),
mMonitor("SyncRunnable"),
mDone(false) {}
nsresult DispatchToThread(nsIEventTarget* aThread,
bool aForceDispatch = false) {
nsresult rv;
bool on;
if (!aForceDispatch) {
rv = aThread->IsOnCurrentThread(&on);
MOZ_ASSERT(NS_SUCCEEDED(rv));
if (NS_SUCCEEDED(rv) && on) {
mRunnable->Run();
return NS_OK;
}
}
rv = aThread->Dispatch(this, NS_DISPATCH_NORMAL);
if (NS_SUCCEEDED(rv)) {
mozilla::MonitorAutoLock lock(mMonitor);
// This could be synchronously dispatching to a thread currently waiting
// for JS execution clearance. Yield JS execution.
dom::AutoYieldJSThreadExecution yield;
while (!mDone) {
lock.Wait();
}
}
return rv;
}
nsresult DispatchToThread(AbstractThread* aThread,
bool aForceDispatch = false) {
if (!aForceDispatch && aThread->IsCurrentThreadIn()) {
mRunnable->Run();
return NS_OK;
}
// Check we don't have tail dispatching here. Otherwise we will deadlock
// ourself when spinning the loop below.
MOZ_ASSERT(!aThread->RequiresTailDispatchFromCurrentThread());
nsresult rv = aThread->Dispatch(RefPtr<nsIRunnable>(this).forget());
if (NS_SUCCEEDED(rv)) {
mozilla::MonitorAutoLock lock(mMonitor);
while (!mDone) {
lock.Wait();
}
}
return rv;
}
static nsresult DispatchToThread(nsIEventTarget* aThread,
nsIRunnable* aRunnable,
bool aForceDispatch = false) {
RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable));
return s->DispatchToThread(aThread, aForceDispatch);
}
static nsresult DispatchToThread(AbstractThread* aThread,
nsIRunnable* aRunnable,
bool aForceDispatch = false) {
RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable));
return s->DispatchToThread(aThread, aForceDispatch);
}
static nsresult DispatchToThread(nsIEventTarget* aThread,
already_AddRefed<nsIRunnable> aRunnable,
bool aForceDispatch = false) {
RefPtr<SyncRunnable> s(new SyncRunnable(std::move(aRunnable)));
return s->DispatchToThread(aThread, aForceDispatch);
}
static nsresult DispatchToThread(AbstractThread* aThread,
already_AddRefed<nsIRunnable> aRunnable,
bool aForceDispatch = false) {
RefPtr<SyncRunnable> s(new SyncRunnable(std::move(aRunnable)));
return s->DispatchToThread(aThread, aForceDispatch);
}
// These deleted overloads prevent accidentally (if harmlessly) double-
// wrapping SyncRunnable, which was previously a common anti-pattern.
static nsresult DispatchToThread(nsIEventTarget* aThread,
SyncRunnable* aRunnable,
bool aForceDispatch = false) = delete;
static nsresult DispatchToThread(AbstractThread* aThread,
SyncRunnable* aRunnable,
bool aForceDispatch = false) = delete;
protected:
NS_IMETHOD Run() override {
mRunnable->Run();
mozilla::MonitorAutoLock lock(mMonitor);
MOZ_ASSERT(!mDone);
mDone = true;
mMonitor.Notify();
return NS_OK;
}
private:
nsCOMPtr<nsIRunnable> mRunnable;
mozilla::Monitor mMonitor;
bool mDone MOZ_GUARDED_BY(mMonitor);
};
} // namespace mozilla
#endif // mozilla_SyncRunnable_h
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