mirror of
https://github.com/kidfromjupiter/nearby.git
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112 lines
3.2 KiB
C++
112 lines
3.2 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_PUBLIC_FUTURE_H_
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#define PLATFORM_PUBLIC_FUTURE_H_
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#include <memory>
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#include <utility>
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#include "absl/base/thread_annotations.h"
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#include "absl/time/time.h"
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#include "internal/platform/condition_variable.h"
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#include "internal/platform/exception.h"
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#include "internal/platform/implementation/system_clock.h"
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#include "internal/platform/mutex.h"
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#include "internal/platform/mutex_lock.h"
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namespace nearby {
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template <typename T>
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class Future final {
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public:
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// Sets the value of the Future.
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bool Set(T value) {
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MutexLock lock(&state_->mutex);
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if (!state_->done) {
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state_->value = ExceptionOr<T>(std::move(value));
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state_->done = true;
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state_->completed.Notify();
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return true;
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}
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return false;
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}
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// Sets the exception of the Future.
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bool SetException(Exception exception) {
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MutexLock lock(&state_->mutex);
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return SetExceptionLocked(exception);
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}
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ExceptionOr<T> Get() {
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MutexLock lock(&state_->mutex);
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while (!state_->done) {
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state_->completed.Wait();
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}
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return state_->value;
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}
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// Gets the value of the Future, timing out after the specified duration.
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ExceptionOr<T> Get(absl::Duration timeout) {
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MutexLock lock(&state_->mutex);
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while (!state_->done) {
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absl::Time start_time = SystemClock::ElapsedRealtime();
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if (state_->completed.Wait(timeout).Raised(Exception::kInterrupted)) {
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SetExceptionLocked({Exception::kInterrupted});
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break;
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}
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absl::Duration spent = SystemClock::ElapsedRealtime() - start_time;
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if (spent < timeout) {
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timeout -= spent;
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} else if (!state_->done) {
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SetExceptionLocked({Exception::kTimeout});
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break;
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}
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}
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return state_->value;
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}
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// Returns true if the Future has been set.
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bool IsSet() const {
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MutexLock lock(&state_->mutex);
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return state_->done;
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}
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private:
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struct FutureState {
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mutable Mutex mutex;
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ConditionVariable completed{&mutex};
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bool done ABSL_GUARDED_BY(mutex) = {false};
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ExceptionOr<T> value ABSL_GUARDED_BY(mutex) =
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ExceptionOr<T>(Exception::kFailed);
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};
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bool SetExceptionLocked(Exception exception) {
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if (!state_->done) {
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state_->value = ExceptionOr<T>(exception.value != Exception::kSuccess
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? exception
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: Exception{Exception::kFailed});
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state_->done = true;
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state_->completed.Notify();
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}
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return true;
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}
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std::shared_ptr<FutureState> state_ = std::make_shared<FutureState>();
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};
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} // namespace nearby
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#endif // PLATFORM_PUBLIC_FUTURE_H_
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