cppdraft_translate/cppdraft/thread/lock.md

[thread.lock]

32 Concurrency support library [thread]

32.6 Mutual exclusion [thread.mutex]

32.6.5 Locks [thread.lock]

32.6.5.1 General [thread.lock.general]

1

#

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]

2

#

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 { }; // do not acquire ownership of the mutexstruct try_to_lock_t { }; // try to acquire ownership of the mutex// without blockingstruct adopt_lock_t { }; // assume the calling thread has already// obtained mutex ownership and manage itinline 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 {templateclass 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; // exposition only};}

1

#

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_guard object.

The supplied Mutex type shall meet the Cpp17BasicLockable requirements ([thread.req.lockable.basic]).

🔗

explicit lock_guard(mutex_type& m);

2

#

Effects: Initializes pm with m.

Calls m.lock().

🔗

lock_guard(mutex_type& m, adopt_lock_t);

3

#

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

4

#

Effects: Initializes pm with m.

5

#

Throws: Nothing.

🔗

~lock_guard();

6

#

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; // Only if sizeof...(MutexTypes) == 1 is trueexplicit 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; // exposition only};}

1

#

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_lock object.

• (1.1)

  If sizeof...(MutexTypes) is one, let Mutex denote the sole type constituting the pack MutexTypes. Mutex shall meet the Cpp17BasicLockable requirements ([thread.req.lockable.basic]). The member typedef-name mutex_type denotes the same type as Mutex.

• (1.2)

  Otherwise, all types in the template parameter pack MutexTypes shall meet the Cpp17Lockable requirements ([thread.req.lockable.req]) and there is no member mutex_type.

🔗

explicit scoped_lock(MutexTypes&... m);

2

#

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);

3

#

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

4

#

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

5

#

Throws: Nothing.

🔗

~scoped_lock();

6

#

Effects: For all i in [0, sizeof...(MutexTypes)),get(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 {templateclass unique_lock {public:using mutex_type = Mutex; // [thread.lock.unique.cons], construct/copy/destroy 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; // [thread.lock.unique.locking], lockingvoid 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(); // [thread.lock.unique.mod], modifiersvoid swap(unique_lock& u) noexcept; mutex_type* release() noexcept; // [thread.lock.unique.obs], observersbool owns_lock() const noexcept; explicit operator bool() const noexcept; mutex_type* mutex() const noexcept; private: mutex_type* pm; // exposition onlybool owns; // exposition only};}

1

#

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.

The suppliedMutex type shall meet the Cpp17BasicLockable requirements ([thread.req.lockable.basic]).

2

#

[Note 1:

unique_lock meets the Cpp17BasicLockable requirements.

If Mutex meets the Cpp17Lockable requirements ([thread.req.lockable.req]),unique_lock also meets the Cpp17Lockable requirements; if Mutex meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]),unique_lock also meets the Cpp17TimedLockable requirements.

— end note]

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

🔗

unique_lock() noexcept;

1

#

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

🔗

explicit unique_lock(mutex_type& m);

2

#

Effects: Calls m.lock().

3

#

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

🔗

unique_lock(mutex_type& m, defer_lock_t) noexcept;

4

#

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

🔗

unique_lock(mutex_type& m, try_to_lock_t);

5

#

Preconditions: The supplied Mutex type meets the Cpp17Lockable requirements ([thread.req.lockable.req]).

6

#

Effects: Calls m.try_lock().

7

#

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);

8

#

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

9

#

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

10

#

Throws: Nothing.

🔗

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

11

#

Preconditions: The supplied Mutex type meets theCpp17TimedLockable requirements ([thread.req.lockable.timed]).

12

#

Effects: Calls m.try_lock_until(abs_time).

13

#

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);

14

#

Preconditions: The supplied Mutex type meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).

15

#

Effects: Calls m.try_lock_for(rel_time).

16

#

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;

17

#

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;

18

#

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

19

#

Returns: *this.

🔗

~unique_lock();

20

#

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

32.6.5.4.3 Locking [thread.lock.unique.locking]

🔗

void lock();

1

#

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

2

#

Postconditions: owns == true.

3

#

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

system_error when an exception is required ([thread.req.exception]).

4

#

Error conditions:

• (4.1)

  operation_not_permitted — if pm is nullptr.

• (4.2)

  resource_deadlock_would_occur — if on entry owns is true.

🔗

bool try_lock();

5

#

Preconditions: The supplied Mutex meets the Cpp17Lockable requirements ([thread.req.lockable.req]).

6

#

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

7

#

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

8

#

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

9

#

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

system_error when an exception is required ([thread.req.exception]).

10

#

Error conditions:

• (10.1)

  operation_not_permitted — if pm is nullptr.

• (10.2)

  resource_deadlock_would_occur — if on entry owns is true.

🔗

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

11

#

Preconditions: The supplied Mutex type meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).

12

#

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

13

#

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

14

#

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

15

#

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

system_error when an exception is required ([thread.req.exception]).

16

#

Error conditions:

• (16.1)

  operation_not_permitted — if pm is nullptr.

• (16.2)

  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);

17

#

Preconditions: The supplied Mutex type meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).

18

#

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

19

#

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

20

#

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

21

#

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

system_error when an exception is required ([thread.req.exception]).

22

#

Error conditions:

• (22.1)

  operation_not_permitted — if pm is nullptr.

• (22.2)

  resource_deadlock_would_occur — if on entry owns istrue.

🔗

void unlock();

23

#

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

24

#

Postconditions: owns == false.

25

#

Throws: system_error when an exception is required ([thread.req.exception]).

26

#

Error conditions:

• (26.1)

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;

1

#

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

🔗

mutex_type* release() noexcept;

2

#

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

3

#

Returns: The previous value of pm.

🔗

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

4

#

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

32.6.5.4.5 Observers [thread.lock.unique.obs]

🔗

bool owns_lock() const noexcept;

1

#

Returns: owns.

🔗

explicit operator bool() const noexcept;

2

#

Returns: owns.

🔗

mutex_type *mutex() const noexcept;

3

#

Returns: pm.

32.6.5.5 Class template shared_lock [thread.lock.shared]

32.6.5.5.1 General [thread.lock.shared.general]

🔗

namespace std {templateclass shared_lock {public:using mutex_type = Mutex; // [thread.lock.shared.cons], 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], 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], modifiersvoid swap(shared_lock& u) noexcept; mutex_type* release() noexcept; // [thread.lock.shared.obs], observersbool owns_lock() const noexcept; explicit operator bool() const noexcept; mutex_type* mutex() const noexcept; private: mutex_type* pm; // exposition onlybool owns; // exposition only};}

1

#

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.

The suppliedMutex type shall meet the Cpp17SharedLockable requirements ([thread.req.lockable.shared]).

2

#

[Note 1:

shared_lock meets the Cpp17Lockable requirements ([thread.req.lockable.req]).

If Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]),shared_lock also meets the Cpp17TimedLockable requirements ([thread.req.lockable.timed]).

— end note]

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

🔗

shared_lock() noexcept;

1

#

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

🔗

explicit shared_lock(mutex_type& m);

2

#

Effects: Calls m.lock_shared().

3

#

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

🔗

shared_lock(mutex_type& m, defer_lock_t) noexcept;

4

#

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

🔗

shared_lock(mutex_type& m, try_to_lock_t);

5

#

Effects: Calls m.try_lock_shared().

6

#

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

🔗

shared_lock(mutex_type& m, adopt_lock_t);

7

#

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

8

#

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

🔗

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

9

#

Preconditions: Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]).

10

#

Effects: Calls m.try_lock_shared_until(abs_time).

11

#

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

🔗

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

12

#

Preconditions: Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]).

13

#

Effects: Calls m.try_lock_shared_for(rel_time).

14

#

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

🔗

~shared_lock();

15

#

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

🔗

shared_lock(shared_lock&& sl) noexcept;

16

#

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.

🔗

shared_lock& operator=(shared_lock&& sl) noexcept;

17

#

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

18

#

Returns: *this.

32.6.5.5.3 Locking [thread.lock.shared.locking]

🔗

void lock();

1

#

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

2

#

Postconditions: owns == true.

3

#

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

system_error when an exception is required ([thread.req.exception]).

4

#

Error conditions:

• (4.1)

  operation_not_permitted — if pm is nullptr.

• (4.2)

  resource_deadlock_would_occur — if on entry owns istrue.

🔗

bool try_lock();

5

#

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

6

#

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

7

#

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

8

#

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

system_error when an exception is required ([thread.req.exception]).

9

#

Error conditions:

• (9.1)

  operation_not_permitted — if pm is nullptr.

• (9.2)

  resource_deadlock_would_occur — if on entry owns istrue.

🔗

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

10

#

Preconditions: Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]).

11

#

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

12

#

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

13

#

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

14

#

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

system_error when an exception is required ([thread.req.exception]).

15

#

Error conditions:

• (15.1)

  operation_not_permitted — if pm is nullptr.

• (15.2)

  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);

16

#

Preconditions: Mutex meets the Cpp17SharedTimedLockable requirements ([thread.req.lockable.shared.timed]).

17

#

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

18

#

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

19

#

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

20

#

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

system_error when an exception is required ([thread.req.exception]).

21

#

Error conditions:

• (21.1)

  operation_not_permitted — if pm is nullptr.

• (21.2)

  resource_deadlock_would_occur — if on entry owns istrue.

🔗

void unlock();

22

#

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

23

#

Postconditions: owns == false.

24

#

Throws: system_error when an exception is required ([thread.req.exception]).

25

#

Error conditions:

• (25.1)

operation_not_permitted — if on entry owns isfalse.

32.6.5.5.4 Modifiers [thread.lock.shared.mod]

🔗

void swap(shared_lock& sl) noexcept;

1

#

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

🔗

mutex_type* release() noexcept;

2

#

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

3

#

Returns: The previous value of pm.

🔗

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

4

#

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

32.6.5.5.5 Observers [thread.lock.shared.obs]

🔗

bool owns_lock() const noexcept;

1

#

Returns: owns.

🔗

explicit operator bool() const noexcept;

2

#

Returns: owns.

🔗

mutex_type* mutex() const noexcept;

3

#

Returns: pm.