// Copyright (c) 2017-2022 Cloudflare, Inc.
// Licensed under the Apache 2.0 license found in the LICENSE file or at:
//     https://opensource.org/licenses/Apache-2.0

#pragma once

#include <kj/async.h>
#include <kj/mutex.h>

namespace workerd {

class XThreadNotifier final: public kj::AtomicRefcounted {
  // Class encapsulating the ability to notify a waiting thread from other threads.
  //
  // TODO(cleanup): Can this be consolidated with wait-list.h?
  //
  // TODO(cleanup): This could be a lot simpler if only it were possible to cancel
  //   an executor.executeAsync() promise from an arbitrary thread. Then, if the inspector
  //   session was destroyed in its thread while a cross-thread notification was in-flight, it
  //   could cancel that notification directly.
 public:
  static inline kj::Own<XThreadNotifier> create() {
    return kj::atomicRefcounted<XThreadNotifier>();
  }

  XThreadNotifier(): paf(kj::newPromiseAndCrossThreadFulfiller<void>()) {}

  kj::Promise<void> awaitNotification() {
    auto promise = kj::mv(paf.lockExclusive()->promise);
    co_await promise;
    auto lockedPaf = paf.lockExclusive();
    auto nextPaf = kj::newPromiseAndCrossThreadFulfiller<void>();
    lockedPaf->promise = kj::mv(nextPaf.promise);
    lockedPaf->fulfiller = kj::mv(nextPaf.fulfiller);
  }

  void notify() const {
    paf.lockExclusive()->fulfiller->fulfill();
  }

 private:
  kj::MutexGuarded<kj::PromiseCrossThreadFulfillerPair<void>> paf;
};

}  // namespace workerd