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// Copyright (c) 2017-2022 Cloudflare, Inc.
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// Licensed under the Apache 2.0 license found in the LICENSE file or at:
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//     https://opensource.org/licenses/Apache-2.0
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#pragma once
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#include <kj/async.h>
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#include <kj/mutex.h>
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namespace workerd {
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class XThreadNotifier final: public kj::AtomicRefcounted {
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  // Class encapsulating the ability to notify a waiting thread from other threads.
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  //
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  // TODO(cleanup): Can this be consolidated with wait-list.h?
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  //
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  // TODO(cleanup): This could be a lot simpler if only it were possible to cancel
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  //   an executor.executeAsync() promise from an arbitrary thread. Then, if the inspector
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  //   session was destroyed in its thread while a cross-thread notification was in-flight, it
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  //   could cancel that notification directly.
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 public:
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  static inline kj::Own<XThreadNotifier> create() {
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    return kj::atomicRefcounted<XThreadNotifier>();
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  }
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  XThreadNotifier(): paf(kj::newPromiseAndCrossThreadFulfiller<void>()) {}
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  kj::Promise<void> awaitNotification() {
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    auto promise = kj::mv(paf.lockExclusive()->promise);
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    co_await promise;
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    auto lockedPaf = paf.lockExclusive();
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    auto nextPaf = kj::newPromiseAndCrossThreadFulfiller<void>();
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    lockedPaf->promise = kj::mv(nextPaf.promise);
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    lockedPaf->fulfiller = kj::mv(nextPaf.fulfiller);
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  }
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  void notify() const {
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    paf.lockExclusive()->fulfiller->fulfill();
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  }
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 private:
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  kj::MutexGuarded<kj::PromiseCrossThreadFulfillerPair<void>> paf;
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};
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}  // namespace workerd