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Latch.h
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Latch.h
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/*
* Copyright (c) 2022, Alibaba Group Holding Limited;
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef ASYNC_SIMPLE_UTHREAD_LATCH_H
#define ASYNC_SIMPLE_UTHREAD_LATCH_H
#include <async_simple/Future.h>
#include <type_traits>
namespace async_simple {
namespace uthread {
// The semantics of uthread::Latch is similar to std::latch. The design of
// uthread::Latch also mimics the design of std::latch. The uthread::Latch is
// used to synchronize different uthread stackful coroutine. The uthread
// stackful coroutine who is awaiting a uthread::Latch would be suspended until
// the counter in the awaited uthread::Latch counted to zero.
//
// Example:
//
// ```C++
// Latch latch(2);
// latch.await();
// // In another uthread
// latch.downCount();
// // In another uthread
// latch.downCount();
// ```
class Latch {
public:
explicit Latch(std::size_t count) : _count(count), _skip(!count) {}
Latch(const Latch&) = delete;
Latch(Latch&&) = delete;
~Latch() {}
public:
void downCount(std::size_t n = 1) {
if (_skip) {
return;
}
auto lastCount = _count.fetch_sub(n, std::memory_order_acq_rel);
if (lastCount == 1u) {
_promise.setValue(true);
}
}
void await(Executor* ex) {
if (_skip) {
return;
}
uthread::await(_promise.getFuture().via(ex));
}
std::size_t currentCount() const {
return _count.load(std::memory_order_acquire);
}
private:
Promise<bool> _promise;
std::atomic<std::size_t> _count;
bool _skip;
};
} // namespace uthread
} // namespace async_simple
#endif // ASYNC_SIMPLE_UTHREAD_LATCH_H