NAME

lock − thread locking. 

SYNOPSIS

include "lock.m"; lock := load Lock Lock->PATH; Semaphore: adt { obtain: fn(s: self ref Semaphore);  release: fn(s: self ref Semaphore);  new: fn(): ref Semaphore; }; init: fn();

DESCRIPTION

Lock provides semaphore-based mutual exclusion.  Init must be called before creating any locks. 

Semaphore.new()
Creates and returns a reference to a new Semaphore (lock). 

s.obtain()
Obtains exclusive access to the lock s. It will block until it can do so.

s.release()
Releases access to the lock s and allows processes waiting on it to proceed. 

EXCEPTIONS

If lock allocation fails, a “lock alloc” exception is raised. 

SOURCE

/appl/lib/lock.b

BUGS

The current implementation uses a pipe and thus two file descriptors for every lock.  On the other hand, when a process exists, garbage collection of file descriptors ensures that locks are relinquished.