std::unique_lock<Mutex>::try_lock

 

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std::unique_lock

Member functions

unique_lock::unique_lock

unique_lock::~unique_lock

unique_lock::operator=

Locking

unique_lock::lock

unique_lock::try_lock

unique_lock::try_lock_for

unique_lock::try_lock_until

unique_lock::unlock

Modifiers

unique_lock::swap

unique_lock::release

Observers

unique_lock::mutex

unique_lock::owns_lock

unique_lock::operator bool

Non-member functions

swap(std::unique_lock)

 

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.

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

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

lock	locks (i.e., takes ownership of) the associated mutex (public member function)
try_lock_for	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)
try_lock_until	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)
unlock	unlocks (i.e., releases ownership of) the associated mutex (public member function)