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std::mutex::unlock

void unlock();

(since C++11)

Unlocks the mutex.

The mutex must be locked by the current thread of execution, otherwise, the behavior is undefined.

This operation synchronizes-with (as defined in std::memory_order) any subsequent lock operation that obtains ownership of the same mutex.

Parameters

(none).

Return value

(none).

Exceptions

Throws nothing.

Notes

unlock() is usually not called directly: std::unique_lock and std::lock_guard are used to manage exclusive locking.

Example

This example shows how lock and unlock can be used to protect shared data.

#include <iostream>
#include <chrono>
#include <thread>
#include <mutex>
 
int g_num = 0;  // protected by g_num_mutex
std::mutex g_num_mutex;
 
void slow_increment(int id) 
{
    for (int i = 0; i < 3; ++i) {
        g_num_mutex.lock();
        int g_num_running = ++g_num;
        g_num_mutex.unlock();
        std::cout << id << " => " << g_num_running << '\n';
 
        std::this_thread::sleep_for(std::chrono::seconds(1));
    }
}
 
int main()
{
    std::thread t1(slow_increment, 0);
    std::thread t2(slow_increment, 1);
    t1.join();
    t2.join();
}

Possible output:

0 => 1
1 => 2
0 => 3
1 => 4
0 => 5
1 => 6