Date: Fri, 23 Oct 1998 21:50:01 -0700 (PDT) From: Daniel Eischen <eischen@vigrid.com> To: freebsd-bugs@FreeBSD.ORG Subject: Re: kern/8375: pthread_cond_wait() spins the CPU Message-ID: <199810240450.VAA11508@freefall.freebsd.org>
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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
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