std:: shared_lock

Defined in header <shared_mutex>
template < class Mutex > class shared_lock ;		(since C++14)

The class shared_lock is a general-purpose shared mutex ownership wrapper allowing deferred locking, timed locking and transfer of lock ownership. Locking a shared_lock locks the associated shared mutex in shared mode (to lock it in exclusive mode, std::unique_lock can be used).

The shared_lock class is movable, but not copyable – it meets the requirements of MoveConstructible and MoveAssignable but not of CopyConstructible or CopyAssignable .

shared_lock meets the Lockable requirements. If Mutex meets the SharedTimedLockable requirements, shared_lock also meets TimedLockable requirements.

In order to wait in a shared mutex in shared ownership mode, std::condition_variable_any can be used ( std::condition_variable requires std::unique_lock and so can only wait in unique ownership mode).

Template parameters

Mutex

-

the type of the shared mutex to lock. The type must meet the SharedLockable requirements

Member types

Type	Definition
mutex_type	Mutex

Member functions

(constructor)	constructs a shared_lock , optionally locking the supplied mutex (public member function)
(destructor)	unlocks the associated mutex (public member function)
operator=	unlocks the mutex, if owned, and acquires ownership of another (public member function)
Shared locking
lock	locks the associated mutex (public member function)
try_lock	tries to lock the associated mutex (public member function)
try_lock_for	tries to lock the associated mutex, for the specified duration (public member function)
try_lock_until	tries to lock the associated mutex, until a specified time point (public member function)
unlock	unlocks the associated mutex (public member function)
Modifiers
swap	swaps the data members with another shared_lock (public member function)
release	disassociates the mutex without unlocking (public member function)
Observers
mutex	returns a pointer to the associated mutex (public member function)
owns_lock	tests whether the lock owns its associated mutex (public member function)
operator bool	tests whether the lock owns its associated mutex (public member function)

Non-member functions

std::swap (std::shared_lock) (C++14)

specializes the std::swap algorithm (function template)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2981	C++17	redundant deduction guide from shared_lock<Mutex> was provided	removed