NAME¶

std::recursive_timed_mutex::try_lock_for - std::recursive_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 );

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)
tries to lock the mutex, returns if the mutex has been
try_lock_until unavailable until specified time point has been reached
(public member function)
unlock unlocks the mutex
(public member function)