From owner-freebsd-bugs  Fri Oct 23 21:50:07 1998
Return-Path: <owner-freebsd-bugs@FreeBSD.ORG>
Received: (from majordom@localhost)
          by hub.freebsd.org (8.8.8/8.8.8) id VAA14220
          for freebsd-bugs-outgoing; Fri, 23 Oct 1998 21:50:07 -0700 (PDT)
          (envelope-from owner-freebsd-bugs@FreeBSD.ORG)
Received: from freefall.freebsd.org (freefall.FreeBSD.ORG [204.216.27.21])
          by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id VAA14205
          for <freebsd-bugs@FreeBSD.org>; Fri, 23 Oct 1998 21:50:05 -0700 (PDT)
          (envelope-from gnats@FreeBSD.org)
Received: (from gnats@localhost)
	by freefall.freebsd.org (8.8.8/8.8.5) id VAA11508;
	Fri, 23 Oct 1998 21:50:01 -0700 (PDT)
Date: Fri, 23 Oct 1998 21:50:01 -0700 (PDT)
Message-Id: <199810240450.VAA11508@freefall.freebsd.org>
To: freebsd-bugs@FreeBSD.ORG
From: Daniel Eischen <eischen@vigrid.com>
Subject: Re: kern/8375: pthread_cond_wait() spins the CPU
Reply-To: Daniel Eischen <eischen@vigrid.com>
Sender: owner-freebsd-bugs@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org

The following reply was made to PR kern/8375; it has been noted by GNATS.

From: Daniel Eischen <eischen@vigrid.com>
To: dima@tejblum.dnttm.rssi.ru, eischen@vigrid.com
Cc: freebsd-gnats-submit@FreeBSD.ORG, jb@FreeBSD.ORG
Subject: Re: kern/8375: pthread_cond_wait() spins the CPU
Date: Sat, 24 Oct 1998 00:46:23 -0400 (EDT)

 BTW, pthread_mutex_lock also has the same problem as
 pthread_cond_wait if thread scheduling comes at an
 inopportune time:
 
 		_SPINLOCK(&(*mutex)->lock);
 
 		/* Process according to mutex type: */
 		switch ((*mutex)->m_type) {
 		/* Fast mutexes do not check for any error conditions: */
 		case MUTEX_TYPE_FAST:
 			/*
 			 * Enter a loop to wait for the mutex to be locked by the
 			 * current thread: 
 			 */
 			while ((*mutex)->m_owner != _thread_run) {
 				/* Check if the mutex is not locked: */
 				if ((*mutex)->m_owner == NULL) {
 					/* Lock the mutex for this thread: */
 					(*mutex)->m_owner = _thread_run;
 				} else {
 					/*
 					 * Join the queue of threads waiting to lock
 					 * the mutex: 
 					 */
 					_thread_queue_enq(&(*mutex)->m_queue, _thread_run);
 
 					/* Unlock the mutex structure: */
 					_SPINUNLOCK(&(*mutex)->lock);
 
 					/* Block signals: */
 					_thread_kern_sched_state(PS_MUTEX_WAIT, __FILE__, __LINE__);
 
 If thread scheduling is kicked off right after the last
 SPINUNLOCK, then you can also have a thread removed
 from the mutex queue, but it'll never get woken up.
 
 Dan Eischen
 eischen@vigrid.com

To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-bugs" in the body of the message