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https://github.com/kidfromjupiter/nearby.git
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90 lines
3.4 KiB
C++
90 lines
3.4 KiB
C++
// Copyright 2020 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#ifndef PLATFORM_BASE_CANCELLATION_FLAG_H_
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#define PLATFORM_BASE_CANCELLATION_FLAG_H_
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#include <memory>
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#include "absl/base/thread_annotations.h"
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#include "absl/container/flat_hash_set.h"
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#include "absl/functional/any_invocable.h"
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#include "absl/synchronization/mutex.h"
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namespace nearby {
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// A cancellation flag to mark an operation has been cancelled and should be
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// cleaned up as soon as possible.
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class CancellationFlag {
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public:
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// The listener for cancellation.
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using CancelListener = absl::AnyInvocable<void()>;
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CancellationFlag();
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explicit CancellationFlag(bool cancelled);
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CancellationFlag(const CancellationFlag &) = delete;
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CancellationFlag &operator=(const CancellationFlag &) = delete;
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CancellationFlag(CancellationFlag &&) = default;
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CancellationFlag &operator=(CancellationFlag &&) = default;
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virtual ~CancellationFlag();
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// Set the flag as cancelled.
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void Cancel() ABSL_LOCKS_EXCLUDED(mutex_);
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// Set the flag as uncancelled. This is needed for the case where the same
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// endpoint is being reused, and callers want to reset the cancellation flag
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// for the new attempt. Without this API, the reused endpoint will
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// use the cancelled flag.
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//
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// It is expected that calleers will only call `Uncancel()` if the flag is
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// already cancelled (check via `Cancelled()`).
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void Uncancel() ABSL_LOCKS_EXCLUDED(mutex_);
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// Returns true if the flag has been set to cancelled.
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bool Cancelled() const ABSL_LOCKS_EXCLUDED(mutex_);
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private:
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friend class CancellationFlagListener;
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friend class CancellationFlagPeer;
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// The registration inserts the pointer of caller's listener callback into
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// `listeners_`, a flat hash set which support the pointer type for hashing
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// function. It conducts that 2 different pointers might point to the same
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// callback function which is unusual and should avoid. Hence we make it as
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// private and use `CancellationFlagListener` as a RAII to wrap the function.
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// The caller should register listener as lambda or absl::AnyInvocable
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// via `CancellationFlagListener`.
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void RegisterOnCancelListener(CancelListener *listener)
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ABSL_LOCKS_EXCLUDED(mutex_);
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// The un-registration erases the pointer of caller's listener callback from
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// `listeners_`. This is paired to RegisterOnCancelListener which is
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// guaranteed to be called under `CancellationFlagListener`.
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void UnregisterOnCancelListener(CancelListener *listener)
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ABSL_LOCKS_EXCLUDED(mutex_);
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int CancelListenersSize() const ABSL_LOCKS_EXCLUDED(mutex_) {
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absl::MutexLock lock(*mutex_);
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return listeners_.size();
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}
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std::unique_ptr<absl::Mutex> mutex_;
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bool cancelled_ ABSL_GUARDED_BY(mutex_) = false;
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absl::flat_hash_set<CancelListener *> ABSL_GUARDED_BY(mutex_) listeners_;
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};
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} // namespace nearby
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#endif // PLATFORM_BASE_CANCELLATION_FLAG_H_
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