33 Concurrency support library [thread]

33.6 Mutual exclusion [thread.mutex]

33.6.5 Locks [thread.lock] Class template shared_lock [thread.lock.shared] General [thread.lock.shared.general]

namespace std { template<class Mutex> class shared_lock { public: using mutex_type = Mutex; // [thread.lock.shared.cons], construct/copy/destroy 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(const shared_lock&) = delete; shared_lock& operator=(const shared_lock&) = delete; shared_lock(shared_lock&& u) noexcept; shared_lock& operator=(shared_lock&& u) noexcept; // [thread.lock.shared.locking], locking 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(); // [thread.lock.shared.mod], modifiers void swap(shared_lock& u) noexcept; mutex_type* release() noexcept; // [thread.lock.shared.obs], observers 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 }; }
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 Cpp17SharedLockable requirements ([thread.req.lockable.shared]).
[Note 1: 
shared_lock<Mutex> meets the Cpp17Lockable requirements ([thread.req.lockable.req]).
If Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]), shared_lock<Mutex> also meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).
— end note]