std::recursive_timed_mutex::try_lock_for

 

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std::recursive_timed_mutex

Member functions

recursive_timed_mutex::recursive_timed_mutex

recursive_timed_mutex::~recursive_timed_mutex

Locking

recursive_timed_mutex::lock

recursive_timed_mutex::try_lock

recursive_timed_mutex::try_lock_for

recursive_timed_mutex::try_lock_until

recursive_timed_mutex::unlock

Native handle

recursive_timed_mutex::native_handle

 

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 the specified duration timeout_duration has elapsed (timeout) or the lock is acquired (owns the mutex), 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 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.

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

#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.

DR	Applied to	Behavior as published	Correct behavior
LWG 2093	C++11	try_lock_for threw nothing	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)