From cppreference.com
voidlock();(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
will be thrown if this number is exceeded.
Prior
operations on the same mutex synchronize-with (as defined in
) this operation.
Parameters
(none)
Return value
(none)
Exceptions
Throws
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.
Notes
lock() is usually not called directly:
,
, and
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<chrono>#include<iostream>#include<mutex>#include<thread>intg_num=0;// protected by g_num_mutexstd::mutexg_num_mutex;voidslow_increment(intid){for(inti=0;i<3;++i){g_num_mutex.lock();++g_num;// note, that the mutex also syncronizes the outputstd::cout<<"id: "<<id<<", g_num: "<<g_num<<'\n';g_num_mutex.unlock();std::this_thread::sleep_for(std::chrono::milliseconds(234));}}intmain(){std::threadt1{slow_increment,0};std::threadt2{slow_increment,1};t1.join();t2.join();}Possible output:
id: 0, g_num: 1 id: 1, g_num: 2 id: 1, g_num: 3 id: 0, g_num: 4 id: 0, g_num: 5 id: 1, g_num: 6 See also