std::shared_lock

C++

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Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

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Utilities library

Strings library

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Iterators library

Numerics library

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Regular expressions library (C++11)

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Technical Specifications

Thread support library

Threads
thread (C++11)
hardware_destructive_interference_sizehardware_constructive_interference_size (C++17)(C++17)
this_thread namespace
get_id (C++11) yield (C++11)	sleep_for (C++11) sleep_until (C++11)
Mutual exclusion
mutex (C++11) recursive_mutex (C++11) shared_mutex (C++17)	timed_mutex (C++11) recursive_timed_mutex (C++11) shared_timed_mutex (C++14)
Generic lock management
lock_guard (C++11) scoped_lock (C++17) unique_lock (C++11) shared_lock (C++14) defer_lock_ttry_to_lock_tadopt_lock_t (C++11)(C++11)(C++11)	lock (C++11) try_lock (C++11) defer_locktry_to_lockadopt_lock (C++11)(C++11)(C++11) once_flag (C++11) call_once (C++11)
Condition variables
condition_variable (C++11)
condition_variable_any (C++11)
notify_all_at_thread_exit (C++11)
cv_status (C++11)
Futures
promise (C++11) future (C++11) shared_future (C++11) packaged_task (C++11) async (C++11)	launch (C++11) future_status (C++11) future_error (C++11) future_category (C++11) future_errc (C++11)

std::shared_lock

Member functions

shared_lock::shared_lock

shared_lock::~shared_lock

shared_lock::operator=

Shared locking

shared_lock::lock

shared_lock::try_lock

shared_lock::try_lock_for

shared_lock::try_lock_until

shared_lock::unlock

Modifiers

shared_lock::swap

shared_lock::release

Observers

shared_lock::mutex

shared_lock::owns_lock

shared_lock::operator bool

Non-member functions

std::swap(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.

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 SharedMutex 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)

specialization of std::swap for shared_lock (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