std::unique_lock<Mutex>::unique_lock
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< cpp | thread | unique lock
| unique_lock() noexcept; |
(1) | (since C++11) |
| unique_lock( unique_lock&& other ) noexcept; |
(2) | (since C++11) |
| explicit unique_lock( mutex_type& m ); |
(3) | (since C++11) |
| unique_lock( mutex_type& m, std::defer_lock_t t ) noexcept; |
(4) | (since C++11) |
| unique_lock( mutex_type& m, std::try_to_lock_t t ); |
(5) | (since C++11) |
| unique_lock( mutex_type& m, std::adopt_lock_t t ); |
(6) | (since C++11) |
| template< class Rep, class Period > unique_lock( mutex_type& m, |
(7) | (since C++11) |
| template< class Clock, class Duration > unique_lock( mutex_type& m, |
(8) | (since C++11) |
Constructs a unique_lock, optionally locking the supplied mutex.
1) Constructs a
unique_lock with no associated mutex.2) Move constructor. Initializes the
unique_lock with the contents of other. Leaves other with no associated mutex.3-8) Constructs a
unique_lock with m as the associated mutex. Additionally:3) Locks the associated mutex by calling m.lock().
4) Does not lock the associated mutex.
5) Tries to lock the associated mutex without blocking by calling m.try_lock(). The behavior is undefined if
Mutex does not satisfy Lockable.6) Assumes the calling thread already holds a non-shared lock (i.e., a lock acquired by
lock, try_lock, try_lock_for, or try_lock_until) on m. The behavior is undefined if not so.7) Tries to lock the associated mutex by calling m.try_lock_for(timeout_duration). Blocks until specified
timeout_duration has elapsed or the lock is acquired, whichever comes first. May block for longer than timeout_duration. The behavior is undefined if Mutex does not satisfy TimedLockable.8) Tries to lock the associated mutex by calling m.try_lock_until(timeout_time). Blocks until specified
timeout_time has been reached or the lock is acquired, whichever comes first. May block for longer than until timeout_time has been reached. The behavior is undefined if Mutex does not satisfy TimedLockable.Parameters
| other | - | another unique_lock to initialize the state with
|
| m | - | mutex to associate with the lock and optionally acquire ownership of |
| t | - | tag parameter used to select constructors with different locking strategies |
| timeout_duration | - | maximum duration to block for |
| timeout_time | - | maximum time point to block until |
Example
Run this code
#include <iostream> #include <mutex> #include <thread> #include <utility> #include <vector> std::mutex m_a, m_b, m_c; int a, b, c = 1; void update() { { // Note: std::lock_guard or atomic<int> can be used instead std::unique_lock<std::mutex> lk(m_a); a++; } { // Note: see std::lock and std::scoped_lock for details and alternatives std::unique_lock<std::mutex> lk_b(m_b, std::defer_lock); std::unique_lock<std::mutex> lk_c(m_c, std::defer_lock); std::lock(lk_b, lk_c); b = std::exchange(c, b+c); } } int main() { std::vector<std::thread> threads; for (unsigned i = 0; i < 12; ++i) threads.emplace_back(update); for (auto& i: threads) i.join(); std::cout << a << "'th and " << a + 1 << "'th Fibonacci numbers: " << b << " and " << c << '\n'; }
Output:
12'th and 13'th Fibonacci numbers: 144 and 233