std::unique_lock::try_lock - cppreference.com (original) (raw)

| 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.

[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).
• 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.

[edit] Example

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

#include #include #include #include #include   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] |