Std::lock_guard (3) Linux Manual Page

std::lock_guard – std::lock_guard

Synopsis

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)
[deleted]

Example

// 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);
    ++g_i;
    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);
    t1.join();
    t2.join();
    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

std::lock_guard (3) Linux Manual Page