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/* MIT License
*
* Copyright (c) 2018 Will Zhang
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef CPPUTIL_READ_WRITE_LOCK_H_
#define CPPUTIL_READ_WRITE_LOCK_H_
#include <mutex>
#include <condition_variable>
namespace cpputil {
class RWLock {
public:
RWLock() : status_(0), waiting_readers_(0), waiting_writers_(0) {}
RWLock(const RWLock&) = delete;
RWLock(RWLock&&) = delete;
RWLock& operator = (const RWLock&) = delete;
RWLock& operator = (RWLock&&) = delete;
void ReadLock() {
std::unique_lock<std::mutex> lck(mtx_);
waiting_readers_ += 1;
read_cv_.wait(lck, [&]() { return waiting_writers_ == 0 && status_ >= 0; });
waiting_readers_ -= 1;
status_ += 1;
}
void WriteLock() {
std::unique_lock<std::mutex> lck(mtx_);
waiting_writers_ += 1;
write_cv_.wait(lck, [&]() { return status_ == 0; });
waiting_writers_ -= 1;
status_ = -1;
}
void UnLock() {
std::unique_lock<std::mutex> lck(mtx_);
if (status_ == -1) {
status_ = 0;
} else {
status_ -= 1;
}
if (waiting_writers_ > 0) {
if (status_ == 0) {
write_cv_.notify_one();
}
} else {
read_cv_.notify_all();
}
}
private:
// -1 : one writer
// 0 : no reader and no writer
// n > 0 : n reader
int32_t status_;
int32_t waiting_readers_;
int32_t waiting_writers_;
std::mutex mtx_;
std::condition_variable read_cv_;
std::condition_variable write_cv_;
};
} // namespace cpputil
#endif // CPPUTIL_READ_WRITE_LOCK_H_
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