[C++] std::shared_mutex

위 그림처럼 하나의 쓰레드가 읽는 동안 다른 쓰레드도 읽어야 할 경우 shared_mutex를 사용한다.

 

1. std::shared_mutex를 사용하지 않은 경우

#include <iostream>
#include <thread>
#include <chrono>
#include <mutex>
#include <shared_mutex>
#include <string_view>

using namespace std::literals;

std::mutex m;
int shared_data = 0;

void Writer() {
    while(1) {
        m.lock();
        shared_data += 1;
        std::cout << "Writer : " << shared_data << std::endl;
        std::this_thread::sleep_for(1s);
        m.unlock();
        std::this_thread::sleep_for(10ms);
    }
}

void Reader(std::string_view name) {
    while(1) {
        m.lock();
        std::cout << "Reader(" << name << "): " << shraed_data << std::endl;
        std::this_thread::sleep_for(500ms);
        m.unlock();
        std::this_thread::sleep_for(10ms);
    }
}

int main() {
    std::thread t1(Writer);
    std::thread t2(Reader, "A");
    std::thread t3(Reader, "B");
    std::thread t4(Reader, "C");
    t1.join();
    t2.join();
    t3.join();
    t4.join();
}

 

위 코드의 결과는 

Writer : 1
Reader(A) : 1
Reader(B) : 1
Reader(C) : 1
Writer : 2
Reader(A) : 2
Reader(B) : 2
Reader(C) : 2

...

# Reader의 출력이 500ms정도의 간격으로 순차적으로 출력됨.

2. std::shared_mutex를 사용한 경우

#include <iostream>
#include <thread>
#include <chrono>
#include <mutex>
#include <shared_mutex>
#include <string_view>

using namespace std::literals;

std::shared_mutex m;
int shared_data = 0;

void Writer() {
    while(1) {
        m.lock();
        shared_data += 1;
        std::cout << "Writer : " << shared_data << std::endl;
        std::this_thread::sleep_for(1s);
        m.unlock();
        std::this_thread::sleep_for(10ms);
    }
}

void Reader(std::string_view name) {
    while(1) {
        m.lock_shared();
        std::cout << "Reader(" << name << "): " << shraed_data << std::endl;
        std::this_thread::sleep_for(500ms);
        m.unlock_shared();
        std::this_thread::sleep_for(10ms);
    }
}

int main() {
    std::thread t1(Writer);
    std::thread t2(Reader, "A");
    std::thread t3(Reader, "B");
    std::thread t4(Reader, "C");
    t1.join();
    t2.join();
    t3.join();
    t4.join();
}

 

위 코드의 결과는

Writer : 1
Reader(C) : 1
Reader(B) : 1
Reader(A) : 1
Writer : 2
Reader(B) : 2
Reader(A) : 2
Reader(C) : 2

...

# Reader의 출력이 3개의 쓰레드가 동시에 됨.