Construct a std::shared_lock instance that manages
the shared-ownership lock on the supplied mutex.
shared_lock(mutex_type& m,std::adopt_lock_t);
The calling thread must own a shared-ownership lock on m.
Constructs a std::shared_lock instance that
references the supplied mutex and takes ownership of the lock on
m held by the calling
thread.
Nothing.
this->owns_lock()==true, this->mutex()==&m.
#include <shared_mutex>