The mutex extensions provide mutual exclusion primitives for synchronising concurrent LispBM processes. These extensions may or may not be present depending on the platform and configuration of LispBM.

Mutual Exclusion

mutex-create

mutex-create creates a mutex for mutual exclusion between concurrent LispBM processes. The form of a mutex-create expression is (mutex-create). Returns a mutex object. Internally the mutex is represented as a dotted pair used as a queue of waiting process IDs, and can be accidentally destroyed by standard list operations.

(define m (mutex-create))

(nil)

mutex-lock

mutex-lock acquires a mutex. The form of a mutex-lock expression is (mutex-lock mutex). If the mutex is unlocked, the calling process acquires it and returns t. If the mutex is already held by another process, the calling process is blocked until the mutex becomes available. A process must not attempt to lock a mutex it already holds, as this will cause a deadlock. It is recommended to use mutex-lock and mutex-unlock together in a wrapper that guarantees unlocking, for example:

(define m (mutex-create))

(nil)

(define with-mutex-do (lambda (mutex expr)
                        (progn 
                            (mutex-lock mutex)
                            (eval expr)
                            (mutex-unlock mutex))))

(closure (mutex expr) 
  (progn 
      (mutex-lock mutex)
      (eval expr)
      (mutex-unlock mutex))
  nil)

(with-mutex-do m '(+ 1 2))

t

mutex-unlock

mutex-unlock releases a mutex. The form of a mutex-unlock expression is (mutex-unlock mutex). Must be called by the same process that holds the lock. Returns t on success and unblocks the next waiting process if any. Returns an error if the mutex is not currently locked.

(define m (mutex-create))

(nil)

(mutex-lock m)

t

(mutex-unlock m)

t

This document was generated by LispBM version 0.38.0