# std::recursive_timed_mutex::try_lock_for

From cppreference.com
< cpp‎ | thread‎ | recursive timed mutex

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

Tries to lock the mutex. Blocks until specified `timeout_duration` has elapsed or the lock is acquired, whichever comes first. On successful lock acquisition returns true, otherwise 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 `steady_clock` is used to measure the duration. If an implementation uses a `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.

### Parameters

timeout_duration | - | minimum duration to block for

### Return value

true if the lock was acquired successfully, otherwise false.

### Exceptions

Any exception thrown by clock, time_point, or duration during the execution (clocks, time points, and durations provided by the standard library never throw)

### Example

Run this code

    #include <iostream>
    #include <mutex>
    #include <chrono>
    #include <thread>
    #include <vector>
    #include <sstream>
    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& i: threads) {
            i.join();
        }
    }

Possible output:

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

### 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)

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/thread/recursive_timed_mutex/try_lock_for&oldid=124201"