std::mutex::unlock

 

C++

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Technical Specifications

 

Thread support library

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thread (C++11)
this_thread namespace
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Mutual exclusion
mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17)	timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14)
Generic lock management
lock_guard (C++11) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)	lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11)
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std::mutex

Member functions

mutex::mutex

mutex::~mutex

Locking

mutex::lock

mutex::try_lock

mutex::unlock

Native handle

mutex::native_handle

 

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 lock, try_lock and unlock in action:

Run this code

#include <iostream>
#include <mutex>
 
int main()
{
    std::mutex test;
    if (test.try_lock()) {
        std::cout << "first try_lock successful\n";
    } else {
        std::cout << "first try_lock NOT successful\n";
        return 0;
    }
 
    test.unlock();
    test.lock();
 
    if (test.try_lock()) {
        std::cout << "second try_lock successful\n";
    } else {
        std::cout << "second try_lock NOT successful\n";
    }
 
    test.lock();  // trying to lock an already-locked std::mutex will 
                  // block program execution, so we'll hang here
}

Possible output:

first try_lock successful
second try_lock NOT successful
(program hangs)

See also

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