pthread_mutex_destroy(3) on macOS

The text 492395530035, as macOS 10.12.6, macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

free resources allocated for a mutex

pthread_mutex_destroy(3) on macOS now