home | help 
std::unique_lock::lock(3)      C++ Standard Libary     std::unique_lock::lock(3)

NAME
     std::unique_lock::lock - std::unique_lock::lock

Synopsis
	void lock();  (since C++11)

	Locks (i.e., takes ownership of) the associated mutex. Effectively calls
	mutex()->lock().

Parameters
	(none)

Return value
	(none)

Exceptions
	  * Any exceptions thrown by mutex()->lock().
	  *  If  there	is  no associated mutex, std::system_error with an error
     code of
	    std::errc::operation_not_permitted.
	  * If the mutex is already locked by this unique_lock (in other  words,
     owns_lock is
	    true), std::system_error with an error code of
	    std::errc::resource_deadlock_would_occur.

Example
	The following example uses lock to re-acquire a mutex that was unlocked.

     // Run this code

      #include <chrono>
      #include <iostream>
      #include <mutex>
      #include <thread>
      #include <vector>

      int main()
      {
	  int counter = 0;
	  std::mutex counter_mutex;
	  std::vector<std::thread> threads;

	  auto worker_task = [&](int id)
	  {
	      std::unique_lock<std::mutex> lock(counter_mutex);
	      ++counter;
	      std::cout << id << ", initial counter: " << counter << '\n';
	      lock.unlock();

	      // don't hold the lock while we simulate an expensive operation
	      std::this_thread::sleep_for(std::chrono::seconds(1));

	      lock.lock();
	      ++counter;
	      std::cout << id << ", final counter: " << counter << '\n';
	  };

	  for (int i = 0; i < 10; ++i)
	      threads.emplace_back(worker_task, i);

	  for (auto& thread : threads)
	      thread.join();
      }

Possible output:
      0, initial counter: 1
      1, initial counter: 2
      2, initial counter: 3
      3, initial counter: 4
      4, initial counter: 5
      5, initial counter: 6
      6, initial counter: 7
      7, initial counter: 8
      8, initial counter: 9
      9, initial counter: 10
      6, final counter: 11
      3, final counter: 12
      4, final counter: 13
      2, final counter: 14
      5, final counter: 15
      0, final counter: 16
      1, final counter: 17
      7, final counter: 18
      9, final counter: 19
      8, final counter: 20

See also
		 tries	to  lock (i.e., takes ownership of) the associated mutex
     without
	try_lock blocking
		 (public member function)
	unlock	 unlocks (i.e., releases ownership of) the associated mutex
		 (public member function)

http://cppreference.com 	   2024.06.10	       std::unique_lock::lock(3)
home | help