2 * lwpSem.c -- lwpSemaphore manipulation.
3 * Copyright (C) 1991-3 Stephen Crane.
5 * This library is free software; you can redistribute it and/or
6 * modify it under the terms of the GNU Library General Public
7 * License as published by the Free Software Foundation; either
8 * version 2 of the License, or (at your option) any later version.
10 * This library is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * Library General Public License for more details.
15 * You should have received a copy of the GNU Library General Public
16 * License along with this library; if not, write to the Free
17 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19 * author: Stephen Crane, (jsc@doc.ic.ac.uk), Department of Computing,
20 * Imperial College of Science, Technology and Medicine, 180 Queen's
21 * Gate, London SW7 2BZ, England.
33 * create a lwpSemaphore.
36 lwpCreateSem(char *name, int count)
40 if (!(new = malloc(sizeof(struct lwpSem))))
42 new->name = strdup(name);
44 new->q.head = new->q.tail = 0;
49 * signal a lwpSemaphore. We only yield here if
50 * the blocked process has a higher priority than ours'.
53 lwpSignal(struct lwpSem *s)
55 lwpStatus(LwpCurrent, "done with semaphore %s", s->name);
57 struct lwpProc *p = lwpGetFirst(&s->q);
58 lwpStatus(LwpCurrent, "activating first waiter");
60 if (LwpCurrent->pri < p->pri) {
61 lwpStatus(p, "priority is higher");
68 * wait on a lwpSemaphore
71 lwpWait(struct lwpSem *s)
73 lwpStatus(LwpCurrent, "checking semaphore %s", s->name);
75 lwpStatus(LwpCurrent, "blocking");
76 lwpAddTail(&s->q, LwpCurrent);