<mutex>

public member function
<mutex>

std::unique_lock::operator bool

explicit operator bool() const noexcept;
Return whether it owns a lock
Returns whether the object owns a lock.

This is true if the managed mutex object was locked (or adopted) by the unique_lock object, and hasn't been unlocked or released since.

In all other cases, it is false.

This is an alias of unique_lock::owns_lock.

Parameters

none

Return value

true is the object owns a lock on the managed mutex object.
false otherwise.

Example

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// unique_lock::operator= example
#include <iostream>       // std::cout
#include <vector>         // std::vector
#include <thread>         // std::thread
#include <mutex>          // std::mutex, std::unique_lock, std::try_to_lock

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

void print_star () {
  std::unique_lock<std::mutex> lck(mtx,std::try_to_lock);
  // print '*' if successfully locked, 'x' otherwise: 
  if (lck)
    std::cout << '*';
  else                    
    std::cout << 'x';
}

int main ()
{
  std::vector<std::thread> threads;
  for (int i=0; i<500; ++i)
    threads.emplace_back(print_star);

  for (auto& x: threads) x.join();

  return 0;
}


Possible output (the amount of 'x' -if any- may vary):

***********************************x*****x******************x*******************
****************x**x*x*x***x***x************************x**************x********
********************************************************************************
********************************************************************************
****************************************************************x***************
***x****************************************************************************
******x**********x**

Data races

The unique_lock object is accessed.
Its managed mutex object is not accessed by the operation.

Exception safety

No-throw guarantee: never throws exceptions.

See also