Hi,
I have an application that repeatedly forks many short-lived child
processes and waits for SIGCHLD notification. Frequently, the
application ends up blocking in the read() call in evsignal_cb().
I think there's a condition where more than one signal is received
and evsignal_handler() is called multiple times before evsignal_cb()
gets called. When evsignal_cb() finally runs, it drains all the
notifications from the socketpair, so the subsequent calls to
evsignal_cb() block in read().
Attached is a patch that fixes the problem in my application, but
I'm not a libevent expert so corrections would be welcome.
--- libevent-1.2a/signal.c.orig 2006-10-27 23:28:57.000000000 -0400
+++ libevent-1.2a/signal.c 2006-12-14 11:19:27.000000000 -0500
@@ -71,7 +71,7 @@
ssize_t n;
n = read(fd, signals, sizeof(signals));
- if (n == -1)
+ if (n == -1 && errno != EAGAIN && errno != EWOULDBLOCK)
event_err(1, "%s: read", __func__);
event_add(ev, NULL);
}
@@ -102,6 +102,7 @@
FD_CLOSEONEXEC(ev_signal_pair[1]);
fcntl(ev_signal_pair[0], F_SETFL, O_NONBLOCK);
+ fcntl(ev_signal_pair[1], F_SETFL, O_NONBLOCK);
event_set(&ev_signal, ev_signal_pair[1], EV_READ,
evsignal_cb, &ev_signal);
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