[#std-shared_lock-0b]
= xref:std.adoc[std]::xref:std/shared_lock-06.adoc[shared_lock]<xref:folly/SharedMutexImpl-09.adoc[folly::SharedMutexImpl<ReaderPriority, Tag_, Atom, Policy>]>
:relfileprefix: ../
:mrdocs:

std::shared_lock specialization for folly::SharedMutexImpl.

== Synopsis

Declared in `<folly/SharedMutex.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
template<
    bool ReaderPriority,
    typename Tag_,
    template<typename> typename Atom,
    typename Policy>
class xref:std/shared_lock-06.adoc[shared_lock]<xref:folly/SharedMutexImpl-09.adoc[folly::SharedMutexImpl<ReaderPriority, Tag_, Atom, Policy>]>;
----

== Description

Uses the tokenful version of unlock_shared for faster unlocking by carrying a token that records where the shared lock was taken.

== Type Aliases

[cols="1,4"]
|===
| Name| Description
| xref:std/shared_lock-0b/mutex_type.adoc[`mutex_type`] 
| The mutex type this lock manages.
| xref:std/shared_lock-0b/token_type.adoc[`token_type`] 
| The token type used to record the shared lock.
|===


== Member Functions

[cols="1,4"]
|===
| Name| Description
| xref:std/shared_lock-0b/2constructor-0c.adoc[`shared_lock`]         [.small]#[constructor]#
| Constructors
| xref:std/shared_lock-0b/2destructor.adoc[`~shared_lock`] [.small]#[destructor]#
| Releases the shared lock if it is held.
| xref:std/shared_lock-0b/operator_assign-06.adoc[`operator=`] 
| Assignment operators
| xref:std/shared_lock-0b/lock.adoc[`lock`] 
| Acquires the managed mutex in shared mode.
| xref:std/shared_lock-0b/mutex.adoc[`mutex`] 
| Returns the managed mutex without releasing ownership.
| xref:std/shared_lock-0b/owns_lock.adoc[`owns_lock`] 
| Reports whether this lock currently owns a shared lock.
| xref:std/shared_lock-0b/release.adoc[`release`] 
| Releases ownership of the managed mutex without unlocking it.
| xref:std/shared_lock-0b/swap.adoc[`swap`] 
| Swaps the managed mutex and token with another lock.
| xref:std/shared_lock-0b/try_lock.adoc[`try_lock`] 
| Tries to acquire the managed mutex in shared mode without blocking.
| xref:std/shared_lock-0b/try_lock_for.adoc[`try_lock_for`] 
| Tries to acquire the managed mutex in shared mode within a duration.
| xref:std/shared_lock-0b/try_lock_until.adoc[`try_lock_until`] 
| Tries to acquire the managed mutex in shared mode by a deadline.
| xref:std/shared_lock-0b/unlock.adoc[`unlock`] 
| Releases the managed shared lock.
| xref:std/shared_lock-0b/2conversion.adoc[`operator bool`] 
| Reports whether this lock currently owns a shared lock.
|===


== Template Parameters

[cols="1,4"]
|===
| Name| Description
| *ReaderPriority*
| Whether the mutex gives priority to readers.
| *Tag_*
| Tag type of the mutex instantiation.
| *Atom*
| Atomic template used by the mutex.
| *Policy*
| Policy type of the mutex.
|===


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