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std::lock_guard(3) C++ Standard Libary std::lock_guard(3) NAME std::lock_guard - std::lock_guard Synopsis Defined in header <mutex> template< class Mutex > (since C++11) 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 ob- ject 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 Basi- cLockable requirements Member types Member type Definition mutex_type Mutex Member functions constructor constructs a lock_guard, optionally locking the given mutex (public member function) destructor destructs the lock_guard object, unlocks the underly- ing mutex (public member function) operator= not copy-assignable [deleted] (public member function) Notes (since C++17) std::scoped_lock offers a replacement for lock_guard that provides the ability to lock multiple mutexes using a deadlock avoidance algo- rithm. 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() { const std::lock_guard<std::mutex> lock(g_i_mutex); ++g_i; std::cout << "g_i: " << g_i << "; in thread #" << std::this_thread::get_id() << '\n'; // g_i_mutex is automatically released when lock // goes out of scope } int main() { std::cout << "g_i: " << g_i << "; in main()\n"; std::thread t1(safe_increment); std::thread t2(safe_increment); t1.join(); t2.join(); std::cout << "g_i: " << g_i << "; in main()\n"; } Possible output: g_i: 0; in main() g_i: 1; in thread #140487981209344 g_i: 2; in thread #140487972816640 g_i: 2; in main() Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior LWG 2981 C++17 redundant deduction guide from removed lock_guard<Mutex> was provided See also unique_lock implements movable mutex ownership wrapper (C++11) (class template) scoped_lock deadlock-avoiding RAII wrapper for multiple mutexes (C++17) (class template) http://cppreference.com 2022.07.31 std::lock_guard(3)
NAME | Synopsis | Template parameters | Member types | Member functions | Notes | Example | Possible output: | See also
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