std::mutex::lock

 

C++

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lock_guard (C++11) unique_lock (C++11) defer_lock_t try_to_lock_t adopt_lock_t (C++11) (C++11) (C++11)	lock (C++11) try_lock (C++11) defer_lock try_to_lock adopt_lock (C++11) (C++11) (C++11)
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std::mutex

Member functions

mutex::mutex

Locking

mutex::lock

mutex::try_lock

mutex::unlock

Native handle

mutex::native_handle

 

void lock();		(since C++11)

Locks the mutex. If another thread has already locked the mutex, a call to lock will block execution until the lock is acquired.

If lock is called by a thread that already owns the mutex, the program may deadlock. Alternatively, if an implementation can detect the deadlock, a resource_deadlock_would_occur error condition may be observed.

The behavior is undefined if the mutex is not unlocked before being destroyed, i.e. some thread still owns it.

Parameters

(none)

Return value

(none)

Exceptions

Throws std::system_error when errors occur, including errors from the underlying operating system that would prevent lock from meeting its specifications. The mutex is not locked in the case of any exception being thrown.

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

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