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cppdraft_translate/cppdraft/thread/lock/shared.md
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[thread.lock.shared]
# 32 Concurrency support library [[thread]](./#thread)
## 32.6 Mutual exclusion [[thread.mutex]](thread.mutex#thread.lock.shared)
### 32.6.5 Locks [[thread.lock]](thread.lock#shared)
#### 32.6.5.5 Class template shared_lock [thread.lock.shared]
#### [32.6.5.5.1](#general) General [[thread.lock.shared.general]](thread.lock.shared.general)
[🔗](#lib:shared_lock)
namespace std {template<class Mutex>class shared_lock {public:using mutex_type = Mutex; // [[thread.lock.shared.cons]](#cons "32.6.5.5.2 Constructors, destructor, and assignment"), 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 "32.6.5.5.3 Locking"), lockingvoid lock(); // blockingbool 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]](#mod "32.6.5.5.4 Modifiers"), modifiersvoid swap(shared_lock& u) noexcept;
mutex_type* release() noexcept; // [[thread.lock.shared.obs]](#obs "32.6.5.5.5 Observers"), observersbool owns_lock() const noexcept; explicit operator bool() const noexcept;
mutex_type* mutex() const noexcept; private: mutex_type* pm; // *exposition only*bool owns; // *exposition only*};}
[1](#general-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8881)
An object of type shared_lock controls the shared ownership of a
lockable object within a scope[.](#general-1.sentence-1)
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[.](#general-1.sentence-2)
Objects of typeshared_lock are not copyable but are movable[.](#general-1.sentence-3)
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]](basic.life "6.8.4 Lifetime")) of the shared_lock object[.](#general-1.sentence-4)
The suppliedMutex type shall meet the [*Cpp17SharedLockable*](thread.req.lockable.shared#:Cpp17SharedLockable "32.2.5.5 Cpp17SharedLockable requirements [thread.req.lockable.shared]") requirements ([[thread.req.lockable.shared]](thread.req.lockable.shared "32.2.5.5 Cpp17SharedLockable requirements"))[.](#general-1.sentence-5)
[2](#general-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8893)
[*Note [1](#general-note-1)*:
shared_lock<Mutex> meets the [*Cpp17Lockable*](thread.req.lockable.req#:Cpp17Lockable "32.2.5.3 Cpp17Lockable requirements [thread.req.lockable.req]") requirements ([[thread.req.lockable.req]](thread.req.lockable.req "32.2.5.3 Cpp17Lockable requirements"))[.](#general-2.sentence-1)
If Mutex meets the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements")),shared_lock<Mutex> also meets the [*Cpp17TimedLockable*](thread.req.lockable.timed#:Cpp17TimedLockable "32.2.5.4 Cpp17TimedLockable requirements [thread.req.lockable.timed]") requirements ([[thread.req.lockable.timed]](thread.req.lockable.timed "32.2.5.4 Cpp17TimedLockable requirements"))[.](#general-2.sentence-2)
— *end note*]
#### [32.6.5.5.2](#cons) Constructors, destructor, and assignment [[thread.lock.shared.cons]](thread.lock.shared.cons)
[🔗](#lib:shared_lock,constructor)
`shared_lock() noexcept;
`
[1](#cons-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8911)
*Postconditions*: pm == nullptr and owns == false[.](#cons-1.sentence-1)
[🔗](#lib:shared_lock,constructor_)
`explicit shared_lock(mutex_type& m);
`
[2](#cons-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8922)
*Effects*: Calls m.lock_shared()[.](#cons-2.sentence-1)
[3](#cons-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8926)
*Postconditions*: pm == addressof(m) and owns == true[.](#cons-3.sentence-1)
[🔗](#lib:shared_lock,constructor__)
`shared_lock(mutex_type& m, defer_lock_t) noexcept;
`
[4](#cons-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8937)
*Postconditions*: pm == addressof(m) and owns == false[.](#cons-4.sentence-1)
[🔗](#lib:shared_lock,constructor___)
`shared_lock(mutex_type& m, try_to_lock_t);
`
[5](#cons-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8948)
*Effects*: Calls m.try_lock_shared()[.](#cons-5.sentence-1)
[6](#cons-6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8952)
*Postconditions*: pm == addressof(m) and owns == res where res is the
value returned by the call to m.try_lock_shared()[.](#cons-6.sentence-1)
[🔗](#lib:shared_lock,constructor____)
`shared_lock(mutex_type& m, adopt_lock_t);
`
[7](#cons-7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8965)
*Preconditions*: The calling thread holds a shared lock on m[.](#cons-7.sentence-1)
[8](#cons-8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8969)
*Postconditions*: pm == addressof(m) and owns == true[.](#cons-8.sentence-1)
[🔗](#lib:shared_lock,constructor_____)
`template<class Clock, class Duration>
shared_lock(mutex_type& m,
const chrono::time_point<Clock, Duration>& abs_time);
`
[9](#cons-9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8982)
*Preconditions*: Mutex meets the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements"))[.](#cons-9.sentence-1)
[10](#cons-10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8987)
*Effects*: Calls m.try_lock_shared_until(abs_time)[.](#cons-10.sentence-1)
[11](#cons-11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L8991)
*Postconditions*: pm == addressof(m) and owns == res where res is the value returned by the call to m.try_lock_shared_until(abs_time)[.](#cons-11.sentence-1)
[🔗](#lib:shared_lock,constructor______)
`template<class Rep, class Period>
shared_lock(mutex_type& m,
const chrono::duration<Rep, Period>& rel_time);
`
[12](#cons-12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9006)
*Preconditions*: Mutex meets the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements"))[.](#cons-12.sentence-1)
[13](#cons-13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9011)
*Effects*: Calls m.try_lock_shared_for(rel_time)[.](#cons-13.sentence-1)
[14](#cons-14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9015)
*Postconditions*: pm == addressof(m) and owns == res where res is
the value returned by the call to m.try_lock_shared_for(rel_time)[.](#cons-14.sentence-1)
[🔗](#lib:shared_lock,destructor)
`~shared_lock();
`
[15](#cons-15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9028)
*Effects*: If owns calls pm->unlock_shared()[.](#cons-15.sentence-1)
[🔗](#lib:shared_lock,constructor_______)
`shared_lock(shared_lock&& sl) noexcept;
`
[16](#cons-16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9039)
*Postconditions*: pm == sl_p.pm and owns == sl_p.owns (wheresl_p is the state of sl just prior to this construction),sl.pm == nullptr and sl.owns == false[.](#cons-16.sentence-1)
[🔗](#lib:operator=,shared_lock)
`shared_lock& operator=(shared_lock&& sl) noexcept;
`
[17](#cons-17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9052)
*Effects*: Equivalent to: shared_lock(std​::​move(sl)).swap(*this)
[18](#cons-18)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9056)
*Returns*: *this[.](#cons-18.sentence-1)
#### [32.6.5.5.3](#locking) Locking [[thread.lock.shared.locking]](thread.lock.shared.locking)
[🔗](#lib:lock,shared_lock)
`void lock();
`
[1](#locking-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9069)
*Effects*: As if by pm->lock_shared()[.](#locking-1.sentence-1)
[2](#locking-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9073)
*Postconditions*: owns == true[.](#locking-2.sentence-1)
[3](#locking-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9077)
*Throws*: Any exception thrown by pm->lock_shared()[.](#locking-3.sentence-1)
system_error when an exception is required ([[thread.req.exception]](thread.req.exception "32.2.2 Exceptions"))[.](#locking-3.sentence-2)
[4](#locking-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9082)
*Error conditions*:
- [(4.1)](#locking-4.1)
operation_not_permitted — if pm is nullptr[.](#locking-4.1.sentence-1)
- [(4.2)](#locking-4.2)
resource_deadlock_would_occur — if on entry owns istrue[.](#locking-4.2.sentence-1)
[🔗](#lib:try_lock,shared_lock)
`bool try_lock();
`
[5](#locking-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9097)
*Effects*: As if by pm->try_lock_shared()[.](#locking-5.sentence-1)
[6](#locking-6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9101)
*Postconditions*: owns == res, where res is the value returned by
the call to pm->try_lock_shared()[.](#locking-6.sentence-1)
[7](#locking-7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9106)
*Returns*: The value returned by the call to pm->try_lock_shared()[.](#locking-7.sentence-1)
[8](#locking-8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9110)
*Throws*: Any exception thrown by pm->try_lock_shared()[.](#locking-8.sentence-1)
system_error when an exception is required ([[thread.req.exception]](thread.req.exception "32.2.2 Exceptions"))[.](#locking-8.sentence-2)
[9](#locking-9)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9115)
*Error conditions*:
- [(9.1)](#locking-9.1)
operation_not_permitted — if pm is nullptr[.](#locking-9.1.sentence-1)
- [(9.2)](#locking-9.2)
resource_deadlock_would_occur — if on entry owns istrue[.](#locking-9.2.sentence-1)
[🔗](#lib:try_lock_until,shared_lock)
`template<class Clock, class Duration>
bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);
`
[10](#locking-10)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9131)
*Preconditions*: Mutex meets the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements"))[.](#locking-10.sentence-1)
[11](#locking-11)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9136)
*Effects*: As if by pm->try_lock_shared_until(abs_time)[.](#locking-11.sentence-1)
[12](#locking-12)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9140)
*Postconditions*: owns == res, where res is the value returned by
the call to pm->try_lock_shared_until(abs_time)[.](#locking-12.sentence-1)
[13](#locking-13)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9145)
*Returns*: The value returned by the call topm->try_lock_shared_until(abs_time)[.](#locking-13.sentence-1)
[14](#locking-14)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9150)
*Throws*: Any exception thrown by pm->try_lock_shared_until(abs_time)[.](#locking-14.sentence-1)
system_error when an exception is required ([[thread.req.exception]](thread.req.exception "32.2.2 Exceptions"))[.](#locking-14.sentence-2)
[15](#locking-15)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9155)
*Error conditions*:
- [(15.1)](#locking-15.1)
operation_not_permitted — if pm is nullptr[.](#locking-15.1.sentence-1)
- [(15.2)](#locking-15.2)
resource_deadlock_would_occur — if on entry owns istrue[.](#locking-15.2.sentence-1)
[🔗](#lib:try_lock_for,shared_lock)
`template<class Rep, class Period>
bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);
`
[16](#locking-16)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9171)
*Preconditions*: Mutex meets the [*Cpp17SharedTimedLockable*](thread.req.lockable.shared.timed#:Cpp17SharedTimedLockable "32.2.5.6 Cpp17SharedTimedLockable requirements [thread.req.lockable.shared.timed]") requirements ([[thread.req.lockable.shared.timed]](thread.req.lockable.shared.timed "32.2.5.6 Cpp17SharedTimedLockable requirements"))[.](#locking-16.sentence-1)
[17](#locking-17)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9176)
*Effects*: As if by pm->try_lock_shared_for(rel_time)[.](#locking-17.sentence-1)
[18](#locking-18)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9180)
*Postconditions*: owns == res, where res is the value returned by the call to pm->try_lock_shared_for(rel_time)[.](#locking-18.sentence-1)
[19](#locking-19)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9184)
*Returns*: The value returned by the call to pm->try_lock_shared_for(rel_time)[.](#locking-19.sentence-1)
[20](#locking-20)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9188)
*Throws*: Any exception thrown by pm->try_lock_shared_for(rel_time)[.](#locking-20.sentence-1)
system_error when an exception is required ([[thread.req.exception]](thread.req.exception "32.2.2 Exceptions"))[.](#locking-20.sentence-2)
[21](#locking-21)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9192)
*Error conditions*:
- [(21.1)](#locking-21.1)
operation_not_permitted — if pm is nullptr[.](#locking-21.1.sentence-1)
- [(21.2)](#locking-21.2)
resource_deadlock_would_occur — if on entry owns istrue[.](#locking-21.2.sentence-1)
[🔗](#lib:unlock,shared_lock)
`void unlock();
`
[22](#locking-22)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9207)
*Effects*: As if by pm->unlock_shared()[.](#locking-22.sentence-1)
[23](#locking-23)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9211)
*Postconditions*: owns == false[.](#locking-23.sentence-1)
[24](#locking-24)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9215)
*Throws*: system_error when an exception is required ([[thread.req.exception]](thread.req.exception "32.2.2 Exceptions"))[.](#locking-24.sentence-1)
[25](#locking-25)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9219)
*Error conditions*:
- [(25.1)](#locking-25.1)
operation_not_permitted — if on entry owns isfalse[.](#locking-25.sentence-1)
#### [32.6.5.5.4](#mod) Modifiers [[thread.lock.shared.mod]](thread.lock.shared.mod)
[🔗](#lib:swap,shared_lock)
`void swap(shared_lock& sl) noexcept;
`
[1](#mod-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9235)
*Effects*: Swaps the data members of *this and sl[.](#mod-1.sentence-1)
[🔗](#lib:release,shared_lock)
`mutex_type* release() noexcept;
`
[2](#mod-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9246)
*Postconditions*: pm == nullptr and owns == false[.](#mod-2.sentence-1)
[3](#mod-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9250)
*Returns*: The previous value of pm[.](#mod-3.sentence-1)
[🔗](#lib:swap,shared_lock_)
`template<class Mutex>
void swap(shared_lock<Mutex>& x, shared_lock<Mutex>& y) noexcept;
`
[4](#mod-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9262)
*Effects*: As if by x.swap(y)[.](#mod-4.sentence-1)
#### [32.6.5.5.5](#obs) Observers [[thread.lock.shared.obs]](thread.lock.shared.obs)
[🔗](#lib:owns_lock,shared_lock)
`bool owns_lock() const noexcept;
`
[1](#obs-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9275)
*Returns*: owns[.](#obs-1.sentence-1)
[🔗](#lib:operator_bool,shared_lock)
`explicit operator bool() const noexcept;
`
[2](#obs-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9286)
*Returns*: owns[.](#obs-2.sentence-1)
[🔗](#lib:mutex,shared_lock)
`mutex_type* mutex() const noexcept;
`
[3](#obs-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/threads.tex#L9297)
*Returns*: pm[.](#obs-3.sentence-1)
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