std::lock_guard (3) - Linux Manuals

std::lock_guard: std::lock_guard


std::lock_guard - std::lock_guard


Defined in header <mutex>
template< class Mutex >
class lock_guard;

The class lock_guard is a mutex wrapper that provides a convenient RAII-style mechanism for owning a mutex for the duration of a scoped block.
When a lock_guard object is created, it attempts to take ownership of the mutex it is given. When control leaves the scope in which the lock_guard object was created, the lock_guard is destructed and the mutex is released.
The lock_guard class is non-copyable.

Template parameters

Mutex - the type of the mutex to lock. The type must meet the BasicLockable requirements

Member types

Member type Definition
mutex_type Mutex

Member functions

              constructs a lock_guard, optionally locking the given mutex
constructor (public member function)
              destructs the lock_guard object, unlocks the underlying mutex
destructor (public member function)

operator= not copy-assignable
              (public member function)


// Run this code

  #include <thread>
  #include <mutex>
  #include <iostream>

  int g_i = 0;
  std::mutex g_i_mutex; // protects g_i

  void safe_increment()
      std::lock_guard<std::mutex> lock(g_i_mutex);

      std::cout << std::this_thread::get_id() << ": " << g_i << '\n';

      // g_i_mutex is automatically released when lock
      // goes out of scope

  int main()
      std::cout << "main: " << g_i << '\n';

      std::thread t1(safe_increment);
      std::thread t2(safe_increment);


      std::cout << "main: " << g_i << '\n';

Possible output:

  main: 0
  140641306900224: 1
  140641298507520: 2
  main: 2

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG_2981 C++17 redundant deduction guide from lock_guard<Mutex> was provided removed

See also

unique_lock implements movable mutex ownership wrapper
            (class template)

scoped_lock deadlock-avoiding RAII wrapper for multiple mutexes
            (class template)