Std::mutex (3) Linux Manual Page

std::mutex – std::mutex

Synopsis

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)
[deleted]

Locking

              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)

Notes

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.

Example

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::this_thread::sleep_for(std::chrono::seconds(2));
    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");
    t1.join();
    t2.join();
    // 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';
    }
}

Output:

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

std::mutex (3) Linux Manual Page