std::unique_lock<Mutex>::try_lock

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< cpp‎ | thread‎ | unique lock
 
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std::unique_lock
 
bool try_lock();
 (since 哋它亢++11)

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).

Example

The following examples try to acquire a mutex that was locked and unlocked.

Run this code
#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();
}

Output: 

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

See also

 locks (i.e., takes ownership of) the associated mutex
(public member function)
attempts to lock (i.e., takes ownership of) the associated TimedLockable mutex, returns if the mutex has been unavailable for the specified time duration
(public member function)
tries to lock (i.e., takes ownership of) the associated TimedLockable mutex, returns if the mutex has been unavailable until specified time point has been reached
(public member function)
unlocks (i.e., releases ownership of) the associated mutex
(public member function)
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