/* -*- 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)

    : Runnable("SyncRunnable")

    , mRunnable(aRunnable)

    , mMonitor("SyncRunnable")

    , mDone(false)

  {

  }

  explicit SyncRunnable(already_AddRefed<nsIRunnable> aRunnable)

    : Runnable("SyncRunnable")

    , mRunnable(std::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