namespace std {
template <class Mutex>
class shared_lock {
public:
typedef Mutex mutex_type;
// Shared locking
shared_lock() noexcept;
explicit shared_lock(mutex_type& m); // blocking
shared_lock(mutex_type& m, defer_lock_t) noexcept;
shared_lock(mutex_type& m, try_to_lock_t);
shared_lock(mutex_type& m, adopt_lock_t);
template <class Clock, class Duration>
shared_lock(mutex_type& m,
const chrono::time_point<Clock, Duration>& abs_time);
template <class Rep, class Period>
shared_lock(mutex_type& m,
const chrono::duration<Rep, Period>& rel_time);
~shared_lock();
shared_lock(shared_lock const&) = delete;
shared_lock& operator=(shared_lock const&) = delete;
shared_lock(shared_lock&& u) noexcept;
shared_lock& operator=(shared_lock&& u) noexcept;
void lock(); // blocking
bool try_lock();
template <class Rep, class Period>
bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
template <class Clock, class Duration>
bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
void unlock();
// Setters
void swap(shared_lock& u) noexcept;
mutex_type* release() noexcept;
// Getters
bool owns_lock() const noexcept;
explicit operator bool () const noexcept;
mutex_type* mutex() const noexcept;
private:
mutex_type* pm; // exposition only
bool owns; // exposition only
};
template <class Mutex>
void swap(shared_lock<Mutex>& x, shared_lock<Mutex>& y) noexcept;
} // std
An object of type shared_lock controls the shared ownership of a lockable object within a scope. Shared ownership of the lockable object may be acquired at construction or after construction, and may be transferred, after acquisition, to another shared_lock object. Objects of type shared_lock are not copyable but are movable. The behavior of a program is undefined if the contained pointer pm is not null and the lockable object pointed to by pm does not exist for the entire remaining lifetime ([basic.life]) of the shared_lock object. The supplied Mutex type shall meet the shared mutex requirements ([thread.sharedtimedmutex.requirements]).
[ Note: shared_lock<Mutex> meets the TimedLockable requirements ([thread.req.lockable.timed]). — end note ]
Effects: Constructs an object of type shared_lock.
Postconditions: pm == nullptr and owns == false.
explicit shared_lock(mutex_type& m);
Requires: The calling thread does not own the mutex for any ownership mode.
Effects: Constructs an object of type shared_lock and calls m.lock_shared().
Postconditions: pm == &m and owns == true.
shared_lock(mutex_type& m, defer_lock_t) noexcept;
Effects: Constructs an object of type shared_lock.
Postconditions: pm == &m and owns == false.
shared_lock(mutex_type& m, try_to_lock_t);
Requires: The calling thread does not own the mutex for any ownership mode.
Effects: Constructs an object of type shared_lock and calls m.try_lock_shared().
Postconditions: pm == &m and owns == res where res is the value returned by the call to m.try_lock_shared().
shared_lock(mutex_type& m, adopt_lock_t);
Requires: The calling thread has shared ownership of the mutex.
Effects: Constructs an object of type shared_lock.
Postconditions: pm == &m and owns == true.
template <class Clock, class Duration>
shared_lock(mutex_type& m,
const chrono::time_point<Clock, Duration>& abs_time);
Requires: The calling thread does not own the mutex for any ownership mode.
Effects: Constructs an object of type shared_lock and calls m.try_lock_shared_until(abs_time).
Postconditions: pm == &m and owns == res where res is the value returned by the call to m.try_lock_shared_until(abs_time).
template <class Rep, class Period>
shared_lock(mutex_type& m,
const chrono::duration<Rep, Period>& rel_time);
Requires: The calling thread does not own the mutex for any ownership mode.
Effects: Constructs an object of type shared_lock and calls m.try_lock_shared_for(rel_time).
Postconditions: pm == &m and owns == res where res is the value returned by the call to m.try_lock_shared_for(rel_time).
Effects: If owns calls pm->unlock_shared().
shared_lock(shared_lock&& sl) noexcept;
Postconditions: pm == &sl_p.pm and owns == sl_p.owns (where sl_p is the state of sl just prior to this construction), sl.pm == nullptr and sl.owns == false.
shared_lock& operator=(shared_lock&& sl) noexcept;
Effects: If owns calls pm->unlock_shared().
Postconditions: pm == &sl_p.pm and owns == sl_p.owns (where sl_p is the state of sl just prior to this assignment), sl.pm == nullptr and sl.owns == false.
Effects: pm->lock_shared().
Postconditions: owns == true.
Throws: Any exception thrown by pm->lock_shared(). system_error if an exception is required ([thread.req.exception]). system_error with an error condition of operation_not_permitted if pm is nullptr. system_error with an error condition of resource_deadlock_would_occur if on entry owns is true.
Effects: pm->try_lock_shared().
Returns: The value returned by the call to pm->try_lock_shared().
Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared().
Throws: Any exception thrown by pm->try_lock_shared(). system_error if an exception is required ([thread.req.exception]). system_error with an error condition of operation_not_permitted if pm is nullptr. system_error with an error condition of resource_deadlock_would_occur if on entry owns is true.
template <class Clock, class Duration>
bool
try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
Effects: pm->try_lock_shared_until(abs_time).
Returns: The value returned by the call to pm->try_lock_shared_until(abs_time).
Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared_until(abs_time).
Throws: Any exception thrown by pm->try_lock_shared_until(abs_time). system_error if an exception is required ([thread.req.exception]). system_error with an error condition of operation_not_permitted if pm is nullptr. system_error with an error condition of resource_deadlock_would_occur if on entry owns is true.
template <class Rep, class Period>
bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
Effects: pm->try_lock_shared_for(rel_time).
Returns: The value returned by the call to pm->try_lock_shared_for(rel_time).
Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared_for(rel_time).
Throws: Any exception thrown by pm->try_lock_shared_for(rel_time). system_error if an exception is required ([thread.req.exception]). system_error with an error condition of operation_not_permitted if pm is nullptr. system_error with an error condition of resource_deadlock_would_occur if on entry owns is true.
Effects: pm->unlock_shared().
Postconditions: owns == false.
Throws: system_error when an exception is required ([thread.req.exception]).
void swap(shared_lock& sl) noexcept;
Effects: Swaps the data members of *this and sl.
mutex_type* release() noexcept;
Returns: The previous value of pm.
Postconditions: pm == nullptr and owns == false.
template <class Mutex>
void swap(shared_lock<Mutex>& x, shared_lock<Mutex>& y) noexcept;
Effects: x.swap(y).
bool owns_lock() const noexcept;
Returns: owns.
explicit operator bool () const noexcept;
Returns: owns.
mutex_type* mutex() const noexcept;
Returns: pm.