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.

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.

Note

A program may deadlock if a thread that already owns a mutex calls lock on that mutex. Alternatively, if an implementation can detect the deadlock, a resource_deadlock_would_occur error condition may be observed.

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();
    ++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)