std::mutex (3) - Linux Manuals

std::mutex: std::mutex


std::mutex - std::mutex


Defined in header <mutex>
class mutex; (since C++11)

The mutex class is a synchronization primitive that can be used to protect shared data from being simultaneously accessed by multiple threads.
mutex offers exclusive, non-recursive ownership semantics:

* A calling thread owns a mutex from the time that it successfully calls either lock or try_lock until it calls unlock.
* When a thread owns a mutex, all other threads will block (for calls to lock) or receive a false return value (for try_lock) if they attempt to claim ownership of the mutex.
* A calling thread must not own the mutex prior to calling lock or try_lock.

The behavior of a program is undefined if a mutex is destroyed while still owned by any threads, or a thread terminates while owning a mutex. The mutex class satisfies all requirements of Mutex and StandardLayoutType.
std::mutex is neither copyable nor movable.

Member types

Member type Definition
native_handle_type(optional) implementation-defined

Member functions

              constructs the mutex
constructor (public member function)
              destroys the mutex
destructor (public member function)

operator= not copy-assignable
              (public member function)


              locks the mutex, blocks if the mutex is not available
lock (public member function)
              tries to lock the mutex, returns if the mutex is not available
try_lock (public member function)
              unlocks the mutex
unlock (public member function)

Native handle

              returns the underlying implementation-defined native handle object
native_handle (public member function)


std::mutex is usually not accessed directly: std::unique_lock, std::lock_guard,
or std::scoped_lock
(since C++17) manage locking in a more exception-safe manner.


This example shows how a mutex can be used to protect a std::map shared between two threads.
// Run this code

  #include <iostream>
  #include <map>
  #include <string>
  #include <chrono>
  #include <thread>
  #include <mutex>

  std::map<std::string, std::string> g_pages;
  std::mutex g_pages_mutex;

  void save_page(const std::string &url)
      // simulate a long page fetch
      std::string result = "fake content";

      std::lock_guard<std::mutex> guard(g_pages_mutex);
      g_pages[url] = result;

  int main()
      std::thread t1(save_page, "http://foo");
      std::thread t2(save_page, "http://bar");

      // safe to access g_pages without lock now, as the threads are joined
      for (const auto &pair : g_pages) {
          std::cout << pair.first << " => " << pair.second << '\n';


  http://bar => fake content
  http://foo => fake content