std::mutex::unlock (3) Linux Manual Page

std::mutex::unlock – std::mutex::unlock

Synopsis

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

(none)

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.
// Run this code

#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();
        ++g_num;
        std::cout << id << " => " << g_num << '\n';
        g_num_mutex.unlock();
        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

See also

         locks the mutex, blocks if the mutex is not available
lock (public member function)
         tries to lock the mutex, returns if the mutex is not available
try_lock (public member function)