std::timed_...ry_lock_for(3)

💅 std::timed_mutex::try_lock_for 💅

Okay bestie, welcome to the C++ Standard Libary manual — this page is literally all about std::timed_mutex::try_lock_for, and yes the name is giving main-character energy because it's the same as the page title. 💖

✨ NAME ✨

std::timed_mutex::try_lock_for — std::timed_mutex::try_lock_for

🌸 Synopsis 🌸

          template< class Rep, class Period >
          bool try_lock_for( const std::chrono::duration<Rep, Period>&
       (since C++11)
          timeout_duration );

So here's the vibe: it tries to lock the mutex. It blocks until either the specified duration timeout_duration has elapsed (timeout) or the lock is acquired (owns the mutex), whichever comes first. On successful lock acquisition it returns true; otherwise it returns false. ✨

If timeout_duration is less or equal timeout_duration.zero(), the function behaves like try_lock(). 🫶

Heads up: this function may block for longer than timeout_duration due to scheduling or resource contention delays. Not a vibe, just facts. 💀

The standard recommends that a std::steady_clock is used to measure the duration. If an implementation uses a std::system_clock instead, the wait time may also be sensitive to clock adjustments. ⏰

As with try_lock(), this function is allowed to fail spuriously and return false even if the mutex was not locked by any other thread at some point during timeout_duration. So if it says no, it might just be being dramatic. 🙈

Prior unlock() operation on the same mutex synchronizes-with (as defined in std::memory_order) this operation if it returns true. 🧚

🚨 If try_lock_for is called by a thread that already owns the mutex, the behavior is undefined. Do not do that, bestie.

🎀 Parameters 🎀

• timeout_duration — minimum duration to block for.

🌟 Return value 🌟

• true if the lock was acquired successfully, otherwise false.

🦋 Exceptions 🦋

Any exception thrown by timeout_duration (durations provided by the standard library never throw).

💅 Example 💅

Run this code, bestie:

// Run this code

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

using namespace std::chrono_literals;

std::mutex cout_mutex; // control access to std::cout
std::timed_mutex mutex;

void job(int id)
{
    std::ostringstream stream;

    for (int i = 0; i < 3; ++i)
    {
        if (mutex.try_lock_for(100ms))
        {
            stream << "success ";
            std::this_thread::sleep_for(100ms);
            mutex.unlock();
        }
        else
            stream << "failed ";

        std::this_thread::sleep_for(100ms);
    }

    std::lock_guard<std::mutex> lock{cout_mutex};
    std::cout << '[' << id << "] " << stream.str() << '\n';
}

int main()
{
    std::vector<std::thread> threads;
    for (int i{0}; i < 4; ++i)
        threads.emplace_back(job, i);

    for (auto& th : threads)
        th.join();
}

🌈 Possible output 🌈

[0] failed failed failed
[3] failed failed success
[2] failed success failed
[1] success failed success

👑 Defect reports 👑

The following behavior-changing defect reports were applied retroactively to previously published C++ standards:

• LWG 2093 — Applied to: C++11; behavior as published: try_lock_for threw nothing; correct behavior: throws timeout-related exceptions.

⭐ See also ⭐

• lock — locks the mutex, blocks if the mutex is not available (public member function)
• try_lock — tries to lock the mutex, returns if the mutex is not available (public member function)
• try_lock_until — tries to lock the mutex, returns if the mutex has been unavailable until specified time point has been reached (public member function)
• unlock — unlocks the mutex (public member function)

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Okay that's the whole page — source: http://cppreference.com, date: 2024.06.10, page: std::timed_...ry_lock_for(3). Bye bestie, go forth and lock responsibly 💖✨