32 Thread support library [thread]

32.5 Mutual exclusion [thread.mutex]

32.5.4 Locks [thread.lock] Class template lock_­guard [thread.lock.guard]

namespace std {
  template<class Mutex>
  class lock_guard {
    using mutex_type = Mutex;

    explicit lock_guard(mutex_type& m);
    lock_guard(mutex_type& m, adopt_lock_t);

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

    mutex_type& pm;             // exposition only
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 Cpp17BasicLockable requirements ([thread.req.lockable.basic]).
explicit lock_guard(mutex_type& m);
Preconditions: If mutex_­type is not a recursive mutex, the calling thread does not own the mutex m.
Effects: Initializes pm with m.
Calls m.lock().
lock_guard(mutex_type& m, adopt_lock_t);
Preconditions: The calling thread owns the mutex m.
Effects: Initializes pm with m.
Throws: Nothing.
Effects: As if by pm.unlock().