std::unique_lock<Mutex>:: try_lock

Tries to lock (i.e., takes ownership of) the associated mutex without blocking. Effectively calls mutex ( ) - > try_lock ( ) .

std::system_error is thrown if there is no associated mutex or if the mutex is already locked by this std::unique_lock .

Parameters

(none)

Return value

true if the ownership of the mutex has been acquired successfully, false otherwise.

Exceptions

• Any exceptions thrown by mutex ( ) - > try_lock ( ) ( Mutex types do not throw in try_lock , but a custom Lockable might).

• If there is no associated mutex, std::system_error with an error code of std::errc::operation_not_permitted .

• If the mutex is already locked by this std::unique_lock , std::system_error with an error code of std::errc::resource_deadlock_would_occur .

Example

#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
 
using namespace std::chrono_literals;
 
int main()
{
    std::mutex counter_mutex;
    std::vector<std::thread> threads;
    using Id = int;
 
    auto worker_task = [&](Id id, std::chrono::seconds wait, std::chrono::seconds acquire)
    {
        // wait for a few seconds before acquiring lock.
        std::this_thread::sleep_for(wait);
 
        std::unique_lock<std::mutex> lock(counter_mutex, std::defer_lock);
        if (lock.try_lock())
            std::cout << '#' << id << ", lock acquired.\n";
        else
        {
            std::cout << '#' << id << ", failed acquiring lock.\n";
            return;
        }
 
        // keep the lock for a while.
        std::this_thread::sleep_for(acquire);
 
        std::cout << '#' << id << ", releasing lock (via destructor).\n";
    };
 
    threads.emplace_back(worker_task, Id{0}, 0s, 2s);
    threads.emplace_back(worker_task, Id{1}, 1s, 0s);
    threads.emplace_back(worker_task, Id{2}, 3s, 0s);
 
    for (auto& thread : threads)
        thread.join();
}

#0, lock acquired.
#1, failed acquiring lock.
#0, releasing lock (via destructor).
#2, lock acquired.
#2, releasing lock (via destructor).

See also