void lock(); | (since C++11) |
Locks the associated mutex. Effectively calls mutex()->lock()
.
Parameters
(none).
Return value
(none).
Exceptions
- Any exceptions thrown by
mutex()->lock()
- If there is no associated mutex,
std::system_error
with an error code ofstd::errc::operation_not_permitted
- If the mutex is already locked by this
unique_lock
(in other words, owns_lock is true),std::system_error
with an error code ofstd::errc::resource_deadlock_would_occur
Example
The following example uses lock
to re-acquire a mutex that was unlocked.
#include <mutex> #include <thread> #include <iostream> #include <vector> #include <chrono> int main() { int counter = 0; std::mutex counter_mutex; std::vector<std::thread> threads; auto worker_task = [&](int id) { std::unique_lock<std::mutex> lock(counter_mutex); ++counter; std::cout << id << ", initial counter: " << counter << '\n'; lock.unlock(); // don't hold the lock while we simulate an expensive operation std::this_thread::sleep_for(std::chrono::seconds(1)); lock.lock(); ++counter; std::cout << id << ", final counter: " << counter << '\n'; }; for (int i = 0; i < 10; ++i) threads.emplace_back(worker_task, i); for (auto &thread : threads) thread.join(); }
Possible output:
0, initial counter: 1 1, initial counter: 2 2, initial counter: 3 3, initial counter: 4 4, initial counter: 5 5, initial counter: 6 6, initial counter: 7 7, initial counter: 8 8, initial counter: 9 9, initial counter: 10 6, final counter: 11 3, final counter: 12 4, final counter: 13 2, final counter: 14 5, final counter: 15 0, final counter: 16 1, final counter: 17 7, final counter: 18 9, final counter: 19 8, final counter: 20
See also
tries to lock the associated mutex, returns if the mutex is not available (public member function) | |
unlocks the associated mutex (public member function) |
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