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std::unique_lock<Mutex>::try_lock

From cppreference.com
< cpp‎ | thread‎ | unique lock
 
 
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bool try_lock();
(since C++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.

Contents

[edit] Parameters

(none)

[edit] Return value

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

[edit] Exceptions

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

[edit] Example

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

#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).

[edit] See also

locks (i.e., takes ownership of) the associated mutex
(public member function) [edit]
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) [edit]
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) [edit]
unlocks (i.e., releases ownership of) the associated mutex
(public member function) [edit]