std::mutex::lock(3)

💖 std::mutex::lock (3) 💖

okay so bestie, this is the std::mutex::lock page from the C++ Standard Libary, and it's all about locking a mutex. no cap, the whole manual-page vibe is here, just with the energy turned all the way up. 🫶

✨ NAME ✨

std::mutex::lock - std::mutex::lock

🌸 Synopsis 🌸

void lock();  (since C++11)

Locks the mutex. If another thread has already locked the mutex, a call to lock will block execution until the lock is acquired.

If lock is called by a thread that already owns the mutex, the behavior is undefined: for example, the program may deadlock. An implementation that can detect the invalid usage is encouraged to throw a std::system_error with error condition resource_deadlock_would_occur instead of deadlocking.

Prior unlock() operations on the same mutex synchronize-with (as defined in std::memory_order) this operation.

🎀 Parameters 🎀

(none) — literally none, bestie. 🎀

🦋 Return value 🦋

(none) — also none, iconic. 🦋

💅 Exceptions 💅

Throws std::system_error when errors occur, including errors from the underlying operating system that would prevent lock from meeting its specifications. The mutex is not locked in the case of any exception being thrown.

⚠️ read that again: if an exception gets thrown, the mutex is not locked. periodt.

🔥 Notes 🔥

lock() is usually not called directly: std::unique_lock, std::scoped_lock, and std::lock_guard are used to manage exclusive locking.

🌈 Example 🌈

This example shows how lock and unlock can be used to protect shared data.

// Run this code

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

int g_num = 0; // protected by g_num_mutex
std::mutex g_num_mutex;

void slow_increment(int id)
{
    for (int i = 0; i < 3; ++i)
    {
        g_num_mutex.lock();
        ++g_num;
        // note, that the mutex also syncronizes the output
        std::cout << "id: " << id << ", g_num: " << g_num << '\n';
        g_num_mutex.unlock();

        std::this_thread::sleep_for(std::chrono::milliseconds(234));
    }
}

int main()
{
    std::thread t1{slow_increment, 0};
    std::thread t2{slow_increment, 1};
    t1.join();
    t2.join();
}

💀 Possible output 💀

id: 0, g_num: 1
id: 1, g_num: 2
id: 1, g_num: 3
id: 0, g_num: 4
id: 0, g_num: 5
id: 1, g_num: 6

👑 See also 👑

• try_lock — tries to lock the mutex, returns if the mutex is not available (public member function)
• unlock — unlocks the mutex (public member function)
• C documentation for mtx_lock

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that's the whole vibe, bestie 💅 this page is std::mutex::lock(3), sourced from http://cppreference.com, version/date 2024.06.10. mwah 🫶