William Ahern wrote:
On Tue, Jan 22, 2008 at 01:06:30AM +0100, Ron Arts wrote:
Hi,
I am using libevent in a multithreaded program, the main
thread containing the libevent loop, and other threads
doing disk I/O. From mail from this list, and the changelogs
I was under the impression that libevent handles signals
better in a multithreaded environment since 1.3, but now
I think I was wrong.
Is it necessary to specifically ignore signals in every
thread I create?
In Unix it's necessary to change the default behavior of SIGPIPE if you
don't want your process killed. libevent, AFAIK, won't do this for you. If
won't independently setup handlers for all the different signals. Most
daemon applications ignore SIGPIPE as part of their initialization. The
default behavior caters to simple shell applications that can't be bothered
to check the return value of a write.
#include signal.h
struct sigaction sa;
sa = sa_initializer;
sa.sa_handler = SIG_IGN;
sa.sa_flags = 0;
sigemptyset(sa.sa_mask);
if (0 != sigaction(SIGPIPE, sa, 0))
err(EXIT_FAILURE, sigaction);
Oops, I'm sorry, I did not make myself clear, while writing the
email I edited it a lot, and forgot to mention that indeed I
ignore SIGPIPE in my initialisation code:
struct event evsigpipe;
event_init();
event_set(evsigpipe, SIGPIPE, EV_SIGNAL|EV_PERSIST, signal_cb, evsigpipe);
event_add(evsigpipe, NULL);
event_dispatch();
void signal_cb(int fd, short event, void *arg)
{
struct event *signal = arg;
extern int reload_database;
switch(EVENT_SIGNAL(signal)) {
case SIGTERM: // sigterm
fprintf(stderr, Killed);
exit(1); break;
case SIGHUP: // sighup
fprintf(stderr, Got SIGHUP);
reload_config = TRUE;
break;
case SIGUSR1: // reload entire database
fprintf(stderr, Got SIGUSR1);
reload_database = TRUE;
break;
default:
fprintf(stderr, %s: got signal %d, __func__, EVENT_SIGNAL(signal));
break;
}
}
But my program is still being killed with SIGPIPE occasionally.
I am using threads, and I presume sometimes one of the other threads
receives the SIGPIPE signal instead of the main thread, and I
*think* that in such a case my program exits.
But what I meant to ask was: isn't libevent supposed (since 1.3) to handle
multithreading and ensure that only one thread receives the signal?
Or should I specifically add code at the beginning of each thread
to ignore SIGPIPE?
Thanks,
Ron
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