/* -*- 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 nsThreadSyncDispatch_h_
#define nsThreadSyncDispatch_h_

#include "mozilla/Atomics.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/SpinEventLoopUntil.h"

#include "nsThreadUtils.h"
#include "LeakRefPtr.h"

class nsThreadSyncDispatch : public mozilla::Runnable {
 public:
  nsThreadSyncDispatch(already_AddRefed<nsIEventTarget> aOrigin,
                       already_AddRefed<nsIRunnable>&& aTask)
      : Runnable("nsThreadSyncDispatch"),
        mOrigin(aOrigin),
        mSyncTask(std::move(aTask)),
        mIsPending(true) {}

  bool IsPending() {
    // This is an atomic acquire on the origin thread.
    return mIsPending;
  }

  void SpinEventLoopUntilComplete(const nsACString& aVeryGoodReasonToDoThis) {
    mozilla::SpinEventLoopUntil(aVeryGoodReasonToDoThis,
                                [&]() -> bool { return !IsPending(); });
  }

 private:
  NS_IMETHOD Run() override {
    if (nsCOMPtr<nsIRunnable> task = mSyncTask.take()) {
      MOZ_ASSERT(!mSyncTask);

      mozilla::DebugOnly<nsresult> result = task->Run();
      MOZ_ASSERT(NS_SUCCEEDED(result), "task in sync dispatch should not fail");

      // We must release the task here to ensure that when the original
      // thread is unblocked, this task has been released.
      task = nullptr;

      // This is an atomic release on the target thread.
      mIsPending = false;

      // unblock the origin thread
      mOrigin->Dispatch(this, NS_DISPATCH_IGNORE_BLOCK_DISPATCH);
    }

    return NS_OK;
  }

  nsCOMPtr<nsIEventTarget> mOrigin;
  // The task is leaked by default when Run() is not called, because
  // otherwise we may release it in an incorrect thread.
  mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
  mozilla::Atomic<bool, mozilla::ReleaseAcquire> mIsPending;
};

#endif  // nsThreadSyncDispatch_h_