Date: Thu, 8 Jul 1999 12:50:02 -0700 (PDT) From: Jin Guojun <j_guojun@lbl.gov> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/11984: pthread_kill cannot kill select() threads, etc. Message-ID: <199907081950.MAA47981@freefall.freebsd.org>
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The following reply was made to PR kern/11984; it has been noted by GNATS.
From: Jin Guojun <j_guojun@lbl.gov>
To: freebsd-gnats-submit@freebsd.org, jin@iss-p1.lbl.gov
Cc:
Subject: Re: kern/11984: pthread_kill cannot kill select() threads, etc.
Date: Thu, 08 Jul 1999 12:46:56 -0700
By tracing downto c_r library, two problems have been found:
(1) pthread_exit(void *status)
{
int sig;
long l;
pthread_t pthread;
/* Check if this thread is already in the process of exiting: */
if ((_thread_run->flags & PTHREAD_EXITING) != 0) {
char msg[128];
snprintf(msg,"Thread %p has called pthread_exit() from a destructor.
POSIX 1003.1 1996 s16.2.5.2 does not allow this!",_thread_run);
PANIC(msg);
}
/* Flag this thread as exiting: */
_thread_run->flags |= PTHREAD_EXITING;
...
}
PTHREAD_EXITING is defined as 0x100, but _thread_run->flags is type of
char.
So, PTHREAD_EXITING can never be checked or set.
(2) _thread_gc(pthread_addr_t arg)
{
....
/*
* Check if this is not the last thread and there is no
* memory to free this time around.
*/
if (!f_done && p_stack == NULL && pthread_cln == NULL) {
/* Get the current time.
*
* Note that we can't use clock_gettime(2) on
2.2.x;
* use gettimeofday(2) instead.
*/
struct timeval abstimeval;
if (gettimeofday(&abstimeval, NULL) != 0)
PANIC("gc cannot get time");
TIMEVAL_TO_TIMESPEC(&abstimeval, &abstime);
/*
* Do a backup poll in 10 seconds if no threads
* die before then.
*/
abstime.tv_sec += 10;
/*
* Wait for a signal from a dying thread or a
* timeout (for a backup poll).
*/
/* Line 215 */ if ((ret = pthread_cond_timedwait(&_gc_cond,
&_gc_mutex, &abstime)) != 0 && ret !=
ETIMEDOUT)
PANIC("gc cannot wait for a signal");
}
/* Unlock the garbage collector mutex: */
if (pthread_mutex_unlock(&_gc_mutex) != 0)
PANIC("Cannot unlock gc mutex");
...
}
Line 215, dying thread will not able to give conditional signal to gc
thread, so the pthread_exit() hang forever.
Fixing: unknown -- it seems to me this logic needs to be tuned.
Working around: force gc exit(0) if timeout; but this is a temp
solution.
-Jin
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