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#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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