module Mutex: Mutextype 
The type of mutexes.
val create : unit -> tReturn a new mutex.
val lock : t -> unitLock the given mutex. Only one thread can have the mutex locked at any time. A thread that attempts to lock a mutex already locked by another thread will suspend until the other thread unlocks the mutex.
Sys_error was not raised for recursive locking
   (platform-dependent behaviour)Sys_error if the mutex is already locked by the thread calling
   Mutex.lock.val try_lock : t -> boolSame as Mutex.lock, but does not suspend the calling thread if
   the mutex is already locked: just return false immediately
   in that case. If the mutex is unlocked, lock it and
   return true.
val unlock : t -> unitUnlock the given mutex. Other threads suspended trying to lock
   the mutex will restart.  The mutex must have been previously locked
   by the thread that calls Mutex.unlock.
Sys_error was not raised when unlocking an unlocked mutex
   or when unlocking a mutex from a different thread.Sys_error if the mutex is unlocked or was locked by another thread.