32 Concurrency support library [thread] (original) (raw)

32.6 Mutual exclusion [thread.mutex]

32.6.5 Locks [thread.lock]

32.6.5.1 General [thread.lock.general]

A lock is an object that holds a reference to a lockable object and may unlock the lockable object during the lock's destruction (such as when leaving block scope).

An execution agent may use a lock to aid in managing ownership of a lockable object in an exception safe manner.

A lock is said to own a lockable object if it is currently managing the ownership of that lockable object for an execution agent.

A lock does not manage the lifetime of the lockable object it references.

[Note 1:

Locks are intended to ease the burden of unlocking the lockable object under both normal and exceptional circumstances.

— _end note_]

Some lock constructors take tag types which describe what should be done with the lockable object during the lock's construction.

namespace std { struct defer_lock_t { }; struct try_to_lock_t { }; struct adopt_lock_t { }; inline constexpr defer_lock_t defer_lock { };inline constexpr try_to_lock_t try_to_lock { };inline constexpr adopt_lock_t adopt_lock { };}

32.6.5.2 Class template lock_guard [thread.lock.guard]

namespace std { template<class Mutex> class lock_guard { public: using mutex_type = Mutex;explicit lock_guard(mutex_type& m); lock_guard(mutex_type& m, adopt_lock_t);~lock_guard(); lock_guard(const lock_guard&) = delete; lock_guard& operator=(const lock_guard&) = delete;private: mutex_type& pm; };}

An object of type lock_guard controls the ownership of a lockable object within a scope.

A lock_guard object maintains ownership of a lockable object throughout the lock_guard object's lifetime.

The behavior of a program is undefined if the lockable object referenced bypm does not exist for the entire lifetime of the lock_guardobject.

explicit lock_guard(mutex_type& m);

Effects: Initializes pm with m.

Calls m.lock().

lock_guard(mutex_type& m, adopt_lock_t);

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

Effects: Initializes pm with m.

Effects: Equivalent to: pm.unlock()

32.6.5.3 Class template scoped_lock [thread.lock.scoped]

namespace std { template<class... MutexTypes> class scoped_lock { public: using mutex_type = see below; explicit scoped_lock(MutexTypes&... m);explicit scoped_lock(adopt_lock_t, MutexTypes&... m);~scoped_lock(); scoped_lock(const scoped_lock&) = delete; scoped_lock& operator=(const scoped_lock&) = delete;private: tuple<MutexTypes&...> pm; };}

An object of type scoped_lock controls the ownership of lockable objects within a scope.

A scoped_lock object maintains ownership of lockable objects throughout the scoped_lock object's lifetime.

The behavior of a program is undefined if the lockable objects referenced bypm do not exist for the entire lifetime of the scoped_lockobject.

• If sizeof...(MutexTypes) is one, let Mutex denote the sole type constituting the pack MutexTypes.
  The member typedef-name mutex_typedenotes the same type as Mutex.

explicit scoped_lock(MutexTypes&... m);

Effects: Initializes pm with tie(m...).

Then if sizeof...(MutexTypes) is 0, no effects.

Otherwise if sizeof...(MutexTypes) is 1, then m.lock().

Otherwise, lock(m...).

explicit scoped_lock(adopt_lock_t, MutexTypes&... m);

Preconditions: The calling thread holds a non-shared lock on each element of m.

Effects: Initializes pm with tie(m...).

Effects: For all i in [0, sizeof...(MutexTypes)),get<i>(pm).unlock().

32.6.5.4 Class template unique_lock [thread.lock.unique]

32.6.5.4.1 General [thread.lock.unique.general]

namespace std { template<class Mutex> class unique_lock { public: using mutex_type = Mutex; unique_lock() noexcept;explicit unique_lock(mutex_type& m); unique_lock(mutex_type& m, defer_lock_t) noexcept; unique_lock(mutex_type& m, try_to_lock_t); unique_lock(mutex_type& m, adopt_lock_t);template<class Clock, class Duration> unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time);template<class Rep, class Period> unique_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time);~unique_lock(); unique_lock(const unique_lock&) = delete; unique_lock& operator=(const unique_lock&) = delete; unique_lock(unique_lock&& u) noexcept; unique_lock& operator=(unique_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(unique_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 unique_lock controls the ownership of a lockable object within a scope.

Ownership of the lockable object may be acquired at construction or after construction, and may be transferred, after acquisition, to another unique_lock object.

Objects of type unique_lock are not copyable but are movable.

The behavior of a program is undefined if the contained pointerpm is not null and the lockable object pointed to by pm does not exist for the entire remaining lifetime ([basic.life]) of the unique_lock object.

32.6.5.4.2 Constructors, destructor, and assignment [thread.lock.unique.cons]

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

explicit unique_lock(mutex_type& m);

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

unique_lock(mutex_type& m, defer_lock_t) noexcept;

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

unique_lock(mutex_type& m, try_to_lock_t);

Effects: Calls m.try_lock().

Postconditions: pm == addressof(m) and owns == res, where res is the value returned by the call to m.try_lock().

unique_lock(mutex_type& m, adopt_lock_t);

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

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

template<class Clock, class Duration> unique_lock(mutex_type& m, const chrono::time_point<Clock, Duration>& abs_time);

Effects: Calls m.try_lock_until(abs_time).

Postconditions: pm == addressof(m) and owns == res, where res is the value returned by the call to m.try_lock_until(abs_time).

template<class Rep, class Period> unique_lock(mutex_type& m, const chrono::duration<Rep, Period>& rel_time);

Effects: Calls m.try_lock_for(rel_time).

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

unique_lock(unique_lock&& u) noexcept;

Postconditions: pm == u_p.pm and owns == u_p.owns (where u_p is the state of u just prior to this construction), u.pm == 0 and u.owns == false.

unique_lock& operator=(unique_lock&& u) noexcept;

Effects: Equivalent to: unique_lock(std​::​move(u)).swap(*this)

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

32.6.5.4.3 Locking [thread.lock.unique.locking]

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

Postconditions: owns == true.

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

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry ownsis true.

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

Postconditions: owns == res, where res is the value returned bypm->try_lock().

Returns: The value returned by pm->try_lock().

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

Error conditions:

• operation_not_permitted — if pm is nullptr.
• resource_deadlock_would_occur — if on entry ownsis true.

template<class Clock, class Duration> bool try_lock_until(const chrono::time_point<Clock, Duration>& abs_time);

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

Postconditions: owns == res, where res is the value returned bypm->try_lock_until(abs_time).

Returns: The value returned by pm->try_lock_until(abs_time).

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

Error conditions:

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

template<class Rep, class Period> bool try_lock_for(const chrono::duration<Rep, Period>& rel_time);

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

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

Returns: The value returned by pm->try_lock_for(rel_time).

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

Postconditions: owns == false.

Error conditions:

• operation_not_permitted — if on entry owns is false.

32.6.5.4.4 Modifiers [thread.lock.unique.mod]

void swap(unique_lock& u) noexcept;

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

mutex_type* release() noexcept;

Postconditions: pm == 0 and owns == false.

Returns: The previous value of pm.

template<class Mutex> void swap(unique_lock<Mutex>& x, unique_lock<Mutex>& y) noexcept;

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

32.6.5.4.5 Observers [thread.lock.unique.obs]

bool owns_lock() const noexcept;

explicit operator bool() const noexcept;

mutex_type *mutex() const noexcept;