std::unique_lock<Mutex>:: ~unique_lock

From cppreference.com
Concurrency support library
Threads
(C++11)
(C++20)
this_thread namespace
(C++11)
(C++11)
Cooperative cancellation
Mutual exclusion
Generic lock management
Condition variables
(C++11)
Semaphores
Latches and Barriers
(C++20)
(C++20)
Futures
(C++11)
(C++11)
(C++11)
Safe Reclamation
Hazard Pointers
Atomic types
(C++11)
(C++20)
Initialization of atomic types
(C++11) (deprecated in C++20)
(C++11) (deprecated in C++20)
Memory ordering
Free functions for atomic operations
Free functions for atomic flags
~unique_lock ( ) ;
(since C++11)

Destroys the lock. If * this has an associated mutex and has acquired ownership of it, the mutex is unlocked.