| Defined in header <mutex> | ||
|---|---|---|
template< class Mutex > class unique_lock; | (since C++11) |
The class unique_lock is a general-purpose mutex ownership wrapper allowing deferred locking, time-constrained attempts at locking, recursive locking, transfer of lock ownership, and use with condition variables.
The class unique_lock is movable, but not copyable -- it meets the requirements of MoveConstructible and MoveAssignable but not of CopyConstructible or CopyAssignable.
The class unique_lock meets the BasicLockable requirements. If Mutex meets the Lockable requirements, unique_lock also meets the Lockable requirements (ex.: can be used in std::lock); if Mutex meets the TimedLockable requirements, unique_lock also meets the TimedLockable requirements.
Template parameters
| Mutex | - | the type of the mutex to lock. The type must meet the BasicLockable requirements |
Member types
| Type | Definition |
|---|---|
mutex_type | Mutex |
Member functions
constructs a unique_lock, optionally locking the supplied mutex (public member function) | |
| (destructor)
| unlocks the associated mutex, if owned (public member function) |
| operator=
| unlocks the mutex, if owned, and acquires ownership of another (public member function) |
Locking | |
| locks the associated mutex (public member function) | |
| tries to lock the associated mutex, returns if the mutex is not available (public member function) | |
attempts to lock the associated TimedLockable mutex, returns if the mutex has been unavailable for the specified time duration (public member function) | |
tries to lock the associated TimedLockable mutex, returns if the mutex has been unavailable until specified time point has been reached (public member function) | |
| unlocks the associated mutex (public member function) | |
Modifiers | |
swaps state with another std::unique_lock (public member function) | |
| disassociates the associated mutex without unlocking it (public member function) | |
Observers | |
| returns a pointer to the associated mutex (public member function) | |
| tests whether the lock owns its associated mutex (public member function) | |
| tests whether the lock owns its associated mutex (public member function) | |
Non-member functions
| (C++11) | specialization of std::swap for unique_lock (function template) |
Example
#include <mutex>
#include <thread>
#include <chrono>
struct Box {
explicit Box(int num) : num_things{num} {}
int num_things;
std::mutex m;
};
void transfer(Box &from, Box &to, int num)
{
// don't actually take the locks yet
std::unique_lock<std::mutex> lock1(from.m, std::defer_lock);
std::unique_lock<std::mutex> lock2(to.m, std::defer_lock);
// lock both unique_locks without deadlock
std::lock(lock1, lock2);
from.num_things -= num;
to.num_things += num;
// 'from.m' and 'to.m' mutexes unlocked in 'unique_lock' dtors
}
int main()
{
Box acc1(100);
Box acc2(50);
std::thread t1(transfer, std::ref(acc1), std::ref(acc2), 10);
std::thread t2(transfer, std::ref(acc2), std::ref(acc1), 5);
t1.join();
t2.join();
}See also
| (C++11) | implements a strictly scope-based mutex ownership wrapper (class template) |
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