text: #include <synch.h> (or #include <thread.h>) int mutex_init(mutex_t *mp, int type, void *arg));
  Use mutex_init(3T) to initialize the mutex pointed to by mp. The type can be one of the following (note that arg is currently ignored). (For POSIX threads, see "pthread_mutex_init(3T)".)
  USYNC_PROCESS The mutex can be used to synchronize threads in this and other processes.
  USYNC_PROCESS_ROBUST The mutex can be used to robustly synchronize threads in this and other processes.
  USYNC_THREAD The mutex can be used to synchronize threads in this process, only.
  When a process dies while holding a USYNC_PROCESS lock, subsequent requestors of that lock hang. This is a problem for systems which dead process receives the lock, but with an error return indicating that the previous owner died it.
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