LOCK(2) LOCK(2)
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 pro-
cess exists, garbage collection of file descriptors ensures
that locks are relinquished.