/* -*- 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 "nsThreadUtils.h" #include "mozilla/AbstractThread.h" #include "mozilla/Monitor.h" #include "mozilla/Move.h" namespace mozilla { /** * This class will wrap a nsIRunnable and dispatch it to the main 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 a convenience wrapper: * SyncRunnable::DispatchToThread(new myrunnable...()); * */ class SyncRunnable : public Runnable { public: explicit SyncRunnable(nsIRunnable* aRunnable) : mRunnable(aRunnable) , mMonitor("SyncRunnable") , mDone(false) { } explicit SyncRunnable(already_AddRefed<nsIRunnable> aRunnable) : mRunnable(Move(aRunnable)) , mMonitor("SyncRunnable") , mDone(false) { } void 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; } } rv = aThread->Dispatch(this, NS_DISPATCH_NORMAL); if (NS_SUCCEEDED(rv)) { mozilla::MonitorAutoLock lock(mMonitor); while (!mDone) { lock.Wait(); } } } void DispatchToThread(AbstractThread* aThread, bool aForceDispatch = false) { if (!aForceDispatch && aThread->IsCurrentThreadIn()) { mRunnable->Run(); return; } // Check we don't have tail dispatching here. Otherwise we will deadlock // ourself when spinning the loop below. MOZ_ASSERT(!aThread->RequiresTailDispatchFromCurrentThread()); aThread->Dispatch(RefPtr<nsIRunnable>(this).forget()); mozilla::MonitorAutoLock lock(mMonitor); while (!mDone) { lock.Wait(); } } static void DispatchToThread(nsIEventTarget* aThread, nsIRunnable* aRunnable, bool aForceDispatch = false) { RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable)); s->DispatchToThread(aThread, aForceDispatch); } static void DispatchToThread(AbstractThread* aThread, nsIRunnable* aRunnable, bool aForceDispatch = false) { RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable)); s->DispatchToThread(aThread, aForceDispatch); } 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; }; } // namespace mozilla #endif // mozilla_SyncRunnable_h