[Libevent-users] SEGV in compare (event_tree_RB_INSERT), or sometimes event_tree_RB_INSERT_COLOR

[Ken Cox]

Um, nevermind :)  I finally was able to reproduce the problem in the lab  
and, well, it was my fault.  It was a very occasional memory stomp.  Sorry  
for the noise.

Ken

On Fri, 10 Aug 2007 14:07:59 -0400, Ken Cox <kenstir at gmail.com> wrote:

> I have a libevent program that wakes up every 20ms and does some  
> processing.  For this I use one event and repeatedly call event_add  
> reusing the same event.  In the field I see occasional crashes in  
> event_tree_RB_INSERT or event_tree_RB_INSERT_COLOR, but I can't  
> reproduce them in the lab or under valgrind.
>
> If you have seen this kind of crash, or can tell I'm doing something  
> dreadfully wrong, or just can give me a general clue, I would greatly  
> appreciate it.
>
> I built on r309 from the SVN trunk.
>
> Here's one such stack.
>
> 	Program terminated with signal 11, Segmentation fault.
> 	#0  compare (a=0x8648924, b=0x1) at event.c:136
> 	136     event.c: No such file or directory.
> 	        in event.c
> 	(gdb) bt
> 	#0  compare (a=0x8648924, b=0x1) at event.c:136
> 	#1  0x08063bcd in event_tree_RB_INSERT (head=0x86481cc, elm=0x8648924)  
> at event.c:170
> 	#2  0x0806406e in event_queue_insert (base=0x86481a0, ev=0x8648924,  
> queue=1) at event.c:847
> 	#3  0x0806429e in event_add (ev=0x8648924, tv=0x86489d4) at event.c:635
> 	#4  0x08055062 in process_cb (fd=-1, what=1, arg=0x86488b0) at foo.c:335
> 	#5  0x080649a4 in event_base_loop (base=0x86481a0, flags=0) at  
> event.c:313
> 	#6  0x08064b4a in event_loop (flags=0) at event.c:364
> 	#7  0x08064b62 in event_dispatch () at event.c:327
> 	#8  0x08057d42 in main (argc=3, argv=0xbf985764) at foo.c:1061
>
> The code looks kind of like this:
>
> struct event timer_ev;
> struct timeval next_wakeup_tv, snooze_tv;
>
> void process_once(void *arg)
> {
> }
>
> /* timer callback, invokes process_once and sets next timer */
> void process_cb(int fd, short what, void *arg)
> {
>    struct timeval now, then;
>    struct timeval delta_tv = {0, 20000};
>
>    process_once(arg);
>
>    /* calculate next wakeup time */
>    timeradd(&next_wakeup_tv, &delta_tv, &then);
>    next_wakeup_tv = then;
>
>    /* calculate snooze time until then; don't allow it to go negative */
>    gettimeofday(&now, NULL);
>    if (timercmp(&then, &now, <))
>      timerclear(&snooze_tv);
>    else
>      timersub(&then, &now, &snooze_tv); /* snooze = then - now */
>    event_add(&timer_ev, &snooze_tv);
>
>    fprintf(stderr, "%s: snooze={%lu, %6lu} next={%lu, %6lu}\n", __func__,
>            snooze_tv.tv_sec, snooze_tv.tv_usec,
>            next_wakeup_tv.tv_sec, next_wakeup_tv.tv_usec);
> }
>
> /* bootstrap timer */
> void start(void *arg)
> {
>    struct timeval now, delta_tv = {0, 20000};
>    event_set(&timer_ev, -1, 0, process_cb, arg);
>    event_add(&timer_ev, &delta_tv);
>    gettimeofday(&now, NULL);
>    timeradd(&now, &delta_tv, &next_wakeup_tv);
> }
>
>
> ==
> Ken
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-- 
-Ken