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Showing content from https://timsong-cpp.github.io/cppwp/n4659/thread.lock below:

33 Thread support library [thread]

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: 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 { };
}

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;   };

  template<class Mutex> lock_guard(lock_guard<Mutex>) -> lock_guard<Mutex>;
}

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 by pm does not exist for the entire lifetime of the lock_­guard object. The supplied Mutex type shall meet the BasicLockable requirements.

explicit lock_guard(mutex_type& m);

Requires: If mutex_­type is not a recursive mutex, the calling thread does not own the mutex m.

Effects: As if by m.lock().

Postconditions: &pm == &m

lock_guard(mutex_type& m, adopt_lock_t);

Requires: The calling thread owns the mutex m.

Postconditions: &pm == &m

~lock_guard();

Effects: As if by pm.unlock().

namespace std {
  template <class... MutexTypes>
  class scoped_lock {
  public:
    using mutex_type = Mutex;  
    explicit scoped_lock(MutexTypes&... m);
    explicit scoped_lock(MutexTypes&... m, adopt_lock_t);
    ~scoped_lock();

    scoped_lock(const scoped_lock&) = delete;
    scoped_lock& operator=(const scoped_lock&) = delete;

  private:
    tuple<MutexTypes&...> pm;   };

  template<class... MutexTypes>
    scoped_lock(scoped_lock<MutexTypes...>) -> scoped_lock<MutexTypes...>;
}

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 by pm do not exist for the entire lifetime of the scoped_­lock object. When sizeof...(MutexTypes) is 1, the supplied Mutex type shall meet the BasicLockable requirements. Otherwise, each of the mutex types shall meet the Lockable requirements.

explicit scoped_lock(MutexTypes&... m);

Requires: If a MutexTypes type is not a recursive mutex, the calling thread does not own the corresponding mutex element of 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(MutexTypes&... m, adopt_lock_t);

Requires: The calling thread owns all the mutexes in m.

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

~scoped_lock();

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

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);

        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;        };

  template<class Mutex> unique_lock(unique_lock<Mutex>) -> unique_lock<Mutex>;

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

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 pointer pm is not null and the lockable object pointed to by pm does not exist for the entire remaining lifetime of the unique_­lock object. The supplied Mutex type shall meet the BasicLockable requirements.

[ Note: unique_­lock<Mutex> meets the BasicLockable requirements. If Mutex meets the Lockable requirements, unique_­lock<Mutex> also meets the Lockable requirements; if Mutex meets the TimedLockable requirements, unique_­lock<Mutex> also meets the TimedLockable requirements.  — end note ]

unique_lock() noexcept;

Effects: Constructs an object of type unique_­lock.

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

explicit unique_lock(mutex_type& m);

Requires: If mutex_­type is not a recursive mutex the calling thread does not own the mutex.

Effects: Constructs an object of type unique_­lock and calls m.lock().

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

unique_lock(mutex_type& m, defer_lock_t) noexcept;

Effects: Constructs an object of type unique_­lock.

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

unique_lock(mutex_type& m, try_to_lock_t);

Requires: The supplied Mutex type shall meet the Lockable requirements. If mutex_­type is not a recursive mutex the calling thread does not own the mutex.

Effects: Constructs an object of type unique_­lock and 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);

Requires: The calling thread owns the mutex.

Effects: Constructs an object of type unique_­lock.

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);

Requires: If mutex_­type is not a recursive mutex the calling thread does not own the mutex. The supplied Mutex type shall meet the TimedLockable requirements.

Effects: Constructs an object of type unique_­lock and 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);

Requires: If mutex_­type is not a recursive mutex the calling thread does not own the mutex. The supplied Mutex type shall meet the TimedLockable requirements.

Effects: Constructs an object of type unique_­lock and 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);

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

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.

[ Note: With a recursive mutex it is possible for both *this and u to own the same mutex before the assignment. In this case, *this will own the mutex after the assignment and u will not.  — end note ]

~unique_lock();

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

void lock();

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

Postconditions: owns == true.

Throws: Any exception thrown by pm->lock(). system_­error when an exception is required ([thread.req.exception]).

Error conditions:

• operation_­not_­permitted — if pm is nullptr.

• resource_­deadlock_­would_­occur — if on entry owns is true.

bool try_lock();

Requires: The supplied Mutex shall meet the Lockable requirements.

Effects: As if by pm->try_­lock().

Returns: The value returned by the call to try_­lock().

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

Throws: Any exception thrown by pm->try_­lock(). system_­error when an exception is required ([thread.req.exception]).

Error conditions:

• operation_­not_­permitted — if pm is nullptr.

• 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);

Requires: The supplied Mutex type shall meet the TimedLockable requirements.

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

Returns: The value returned by the call to try_­lock_­until(abs_­time).

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

Throws: Any exception thrown by pm->try_­lock_­until(). system_­error when an exception is required ([thread.req.exception]).

Error conditions:

• operation_­not_­permitted — if pm is nullptr.

• resource_­deadlock_­would_­occur — if on entry owns is true.

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

Requires: The supplied Mutex type shall meet the TimedLockable requirements.

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

Returns: The value returned by the call to try_­lock_­until(rel_­time).

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

Throws: Any exception thrown by pm->try_­lock_­for(). system_­error when an exception is required ([thread.req.exception]).

Error conditions:

• operation_­not_­permitted — if pm is nullptr.

• resource_­deadlock_­would_­occur — if on entry owns is true.

void unlock();

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

Postconditions: owns == false.

Error conditions:

• operation_­not_­permitted — if on entry owns is false.

void swap(unique_lock& u) noexcept;

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

mutex_type* release() noexcept;

Returns: The previous value of pm.

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

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

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

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