[thread.lock.shared] (original) (raw)

32 Concurrency support library [thread]

32.6 Mutual exclusion [thread.mutex]

32.6.5 Locks [thread.lock]

32.6.5.5 Class template shared_lock [thread.lock.shared]

32.6.5.5.1 General [thread.lock.shared.general]

namespace std { template<class Mutex> class shared_lock { public: using mutex_type = Mutex; shared_lock() noexcept;explicit shared_lock(mutex_type& m); 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;void lock(); 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();void swap(shared_lock& u) noexcept; mutex_type* release() noexcept;bool owns_lock() const noexcept;explicit operator bool() const noexcept; mutex_type* mutex() const noexcept;private: mutex_type* pm; bool owns; };}

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 typeshared_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.

32.6.5.5.2 Constructors, destructor, and assignment [thread.lock.shared.cons]

Postconditions: pm == nullptr and owns == false.

Effects: Calls m.lock_shared().

Postconditions: pm == addressof(m) and owns == true.

Postconditions: pm == addressof(m) and owns == false.

Effects: Calls m.try_lock_shared().

Postconditions: pm == addressof(m) and owns == reswhere res is the value returned by the call to m.try_lock_shared().

Preconditions: The calling thread holds a shared lock on m.

Postconditions: pm == addressof(m) and owns == true.

Effects: Calls m.try_lock_shared_until(abs_time).

Postconditions: pm == addressof(m) and owns == reswhere resis the value returned by the call to m.try_lock_shared_until(abs_time).

Effects: Calls m.try_lock_shared_for(rel_time).

Postconditions: pm == addressof(m) and owns == reswhere res is the value returned by the call to m.try_lock_shared_for(rel_time).

Effects: If owns calls pm->unlock_shared().

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.

Effects: Equivalent to: shared_lock(std​::​move(sl)).swap(*this)

32.6.5.5.3 Locking [thread.lock.shared.locking]

Effects: As if by pm->lock_shared().

Postconditions: owns == true.

Throws: Any exception thrown by pm->lock_shared().

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry owns istrue.

Effects: As if by pm->try_lock_shared().

Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared().

Returns: The value returned by the call to pm->try_lock_shared().

Throws: Any exception thrown by pm->try_lock_shared().

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry owns istrue.

Effects: As if by pm->try_lock_shared_until(abs_time).

Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared_until(abs_time).

Returns: The value returned by the call topm->try_lock_shared_until(abs_time).

Throws: Any exception thrown by pm->try_lock_shared_until(abs_time).

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry owns istrue.

Effects: As if by pm->try_lock_shared_for(rel_time).

Postconditions: owns == res, where res is the value returned by the call to pm->try_lock_shared_for(rel_time).

Returns: The value returned by the call to pm->try_lock_shared_for(rel_time).

Throws: Any exception thrown by pm->try_lock_shared_for(rel_time).

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry owns istrue.

Effects: As if by pm->unlock_shared().

Postconditions: owns == false.

Error conditions:

• operation_not_permitted — if on entry owns isfalse.

32.6.5.5.4 Modifiers [thread.lock.shared.mod]

Effects: Swaps the data members of *this and sl.

Postconditions: pm == nullptr and owns == false.

Returns: The previous value of pm.

Effects: As if by x.swap(y).