std::unique_lock<Mutex>::lock
From cppreference.com
void lock(); |
(since C++11) | |
Locks (i.e., takes ownership of) 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 of std::errc::operation_not_permitted.
- If the mutex is already locked by this
unique_lock(in other words, owns_lock() istrue), std::system_error with an error code of std::errc::resource_deadlock_would_occur.
Example
The following example uses lock to re-acquire a mutex that was unlocked.
Run this code
#include <chrono>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
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 (i.e., takes ownership of) the associated mutex without blocking (public member function) | |
| unlocks (i.e., releases ownership of) the associated mutex (public member function) |