std::recurs...ry_lock_for(3)

💖 NAME 💖

okay so this is the std::recurs...ry_lock_for(3) page from the C++ Standard Library, and the name is literally std::recursive_timed_mutex::try_lock_for — std::recursive_timed_mutex::try_lock_for. yes bestie, twice, it’s giving main character energy 💅.

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✨ Synopsis ✨

Since C++11, bestie:

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

Tries to lock the mutex. It blocks until 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().

This function may block for longer than timeout_duration due to scheduling or resource contention delays.

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.

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

A thread may call try_lock_for on a recursive mutex repeatedly. Successful calls to try_lock_for increment the ownership count: the mutex will only be released after the thread makes a matching number of calls to unlock().

The maximum number of levels of ownership is unspecified. A call to try_lock_for will return false if this number is exceeded.

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🎀 Parameters 🎀

• timeout_duration — minimum duration to block for.

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🌸 Return value 🌸

true if the lock was acquired successfully, otherwise false.

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🦋 Exceptions 🦋

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

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🔥 Example 🔥

The example says // Run this code — so go off, bestie:

#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();
}

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⭐ Possible output ⭐

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

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💅 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.

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👑 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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mwah 💋 source/version: http://cppreference.com · date: 2024.06.10 · page: std::recurs...ry_lock_for(3) 🫶✨