<mutex>

class template
<mutex>

std::unique_lock

template <class Mutex> class unique_lock;
Unique lock
A unique lock is an object that manages a mutex object with unique ownership in both states: locked and unlocked.

On construction (or by move-assigning to it), the object acquires a mutex object, for whose locking and unlocking operations becomes responsible.

The object supports both states: locked and unlocked.

This class guarantees an unlocked status on destruction (even if not called explicitly). Therefore it is especially useful as an object with automatic duration, as it guarantees the mutex object is properly unlocked in case an exception is thrown.

Note though, that the unique_lock object does not manage the lifetime of the mutex object in any way: the duration of the mutex object shall extend at least until the destruction of the unique_lock that manages it.

Template parameters

Mutex
A mutex-like type.
It shall be a basic lockable type, such as mutex (see BasicLockable for requirements).

Member types

member typedefinitiondescription
mutex_typeThe template parameter (Mutex)The managed mutex object type

Member functions


Locking/unlocking


Modifiers


Observers


Non-member overloads


Example

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// unique_lock example
#include <iostream>       // std::cout
#include <thread>         // std::thread
#include <mutex>          // std::mutex, std::unique_lock

std::mutex mtx;           // mutex for critical section

void print_block (int n, char c) {
  // critical section (exclusive access to std::cout signaled by lifetime of lck):
  std::unique_lock<std::mutex> lck (mtx);
  for (int i=0; i<n; ++i) { std::cout << c; }
  std::cout << '\n';
}

int main ()
{
  std::thread th1 (print_block,50,'*');
  std::thread th2 (print_block,50,'$');

  th1.join();
  th2.join();

  return 0;
}


Possible output (order of lines may vary, but characters are never mixed):

**************************************************
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$