std::recursive_mutex::lock

 

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std::recursive_mutex

Member functions

recursive_mutex::recursive_mutex

Locking

recursive_mutex::lock

recursive_mutex::try_lock

recursive_mutex::unlock

Native handle

recursive_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. A thread may call lock on a recursive mutex repeatedly. Ownership will only be released after the thread makes a matching number of calls to unlock.

The maximum number of levels of ownership is unspecified. An exception of type std::system_error will be thrown if this number is exceeded.

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.

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)