Messages in this thread | | | Subject | sigwait() breaks when straced | Date | Sat, 30 Jul 2005 19:50:10 -0400 | From | Sanjoy Mahajan <> |
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Pavel Machek wrote: > If you think it is a linux bug, can you produce small test case doing > just the sigwait, and post it on l-k with big title "sigwait() breaks > when straced, and on suspend"?
Here it is. I haven't tested the sigwait()+suspend lately, since suspend isn't working with any kernel except 2.6.11.4 and I'm chasing down other acpi errors in 2.6.13-*. But here's a test case for how sigwait() breaks when straced (see C file below). It is with 2.6.13-rc4 on a Thinkpad 600X (Pentium III), Debian 'testing', libc 2.3.2.
$ gcc waiting.c -o waiting -lpthread $ ./waiting Sigwaiting...[strace my pid, which is 3359] [in another shell I run 'strace -p 3359', and get:] sigwait() returned 4, errno=0, sig=77
In the strace window, I get
$ strace -p 3359 Process 3359 attached - interrupt to quit write(2, "sigwait() returned 4, errno=0, s"..., 39) = 39 exit_group(4) = ? Process 3359 detached
According to the man entry for sigwait:
The !sigwait! function never returns an error.
so the return value should not be 4 (or the docs are not right).
Here's waiting.c:
#include <stdio.h> #include <pthread.h> #include <signal.h> #include <errno.h>
sigset_t mask;
int main () { int ret, id; int sig = 77; /* easy to see if it gets changed */
id = getpid(); sigemptyset(&mask); fprintf (stderr, "Sigwaiting...[strace my pid, which is %d]\n", id); ret = sigwait(&mask, &sig); fprintf (stderr, "sigwait() returned %d, errno=%d, sig=%d\n", ret, errno, sig); return ret; }
-Sanjoy
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