Add new evsignal_add_with_flags() for signal events

By default libevent set SA_RESTART flag for sigaction(2), which will restart
syscall automatically, and this is not always good.
(That because it need to be compitable with signal(2), while it vary
across systems)

This patch add new function evsignal_add_with_flags(), which will change
this flag from default SA_RESTART to user defined.

event-internal.h

@@ -52,6 +52,7 @@ extern "C" {
 /* used only by signals */
 #define ev_ncalls	ev_.ev_signal.ev_ncalls
 #define ev_pncalls	ev_.ev_signal.ev_pncalls
+#define ev_sa_flags	ev_.ev_signal.sa_flags
 
 #define ev_pri ev_evcallback.evcb_pri
 #define ev_flags ev_evcallback.evcb_flags
@@ -400,7 +401,7 @@ struct event_config {
 	((base)->event_count_active)
 
 int evsig_set_handler_(struct event_base *base, int evsignal,
-			  void (*fn)(int));
+			  void (*fn)(int), int);
 int evsig_restore_handler_(struct event_base *base, int evsignal);
 
 int event_add_nolock_(struct event *ev,

event.c

@@ -2090,6 +2090,8 @@ event_new(struct event_base *base, evutil_socket_t fd, short events, void (*cb)(
 	ev = mm_malloc(sizeof(struct event));
 	if (ev == NULL)
 		return (NULL);
+
+	ev->ev_sa_flags = SA_RESTART;
 	if (event_assign(ev, base, fd, events, cb, arg) < 0) {
 		mm_free(ev);
 		return (NULL);
@@ -2378,6 +2380,14 @@ event_add(struct event *ev, const struct timeval *tv)
 	return (res);
 }
 
+int
+evsignal_add_with_flags(struct event *ev, const struct timeval *tv, int flags)
+{
+	ev->ev_sa_flags = flags;
+
+	return evsignal_add(ev, tv);
+}
+
 /* Helper callback: wake an event_base from another thread.  This version
  * works by writing a byte to one end of a socketpair, so that the event_base
  * listening on the other end will wake up as the corresponding event

evmap.c

@@ -454,7 +454,7 @@ evmap_signal_add_(struct event_base *base, int sig, struct event *ev)
 	    base->evsigsel->fdinfo_len);
 
 	if (LIST_EMPTY(&ctx->events)) {
-		if (evsel->add(base, ev->ev_fd, 0, EV_SIGNAL, NULL)
+		if (evsel->add(base, ev->ev_fd, 0, EV_SIGNAL, (void *)&ev->ev_sa_flags)
 		    == -1)
 			return (-1);
 	}

include/event2/event.h

@@ -968,6 +968,13 @@ int event_base_got_break(struct event_base *);
 #define evtimer_initialized(ev)		event_initialized(ev)
 /**@}*/
 
+
+/**
+ * Change default sa_flags for sigaction(2) from SA_RESTART
+ * to user-specific.
+ */
+int evsignal_add_with_flags(struct event *, const struct timeval *, int);
+
 /**
    @name evsignal_* macros
 

include/event2/event_struct.h

@@ -145,6 +145,8 @@ struct event {
 			short ev_ncalls;
 			/* Allows deletes in callback */
 			short *ev_pncalls;
+			/* Passed to sigaction(). */
+			int sa_flags;
 		} ev_signal;
 	} ev_;
 

signal.c

@@ -210,7 +210,8 @@ evsig_init_(struct event_base *base)
  * we can restore the original handler when we clear the current one. */
 int
 evsig_set_handler_(struct event_base *base,
-    int evsignal, void (__cdecl *handler)(int))
+    int evsignal, void (__cdecl *handler)(int),
+    int sa_flags)
 {
 #ifdef EVENT__HAVE_SIGACTION
 	struct sigaction sa;
@@ -252,7 +253,7 @@ evsig_set_handler_(struct event_base *base,
 #ifdef EVENT__HAVE_SIGACTION
 	memset(&sa, 0, sizeof(sa));
 	sa.sa_handler = handler;
-	sa.sa_flags |= SA_RESTART;
+	sa.sa_flags |= sa_flags;
 	sigfillset(&sa.sa_mask);
 
 	if (sigaction(evsignal, &sa, sig->sh_old[evsignal]) == -1) {
@@ -278,7 +279,7 @@ static int
 evsig_add(struct event_base *base, evutil_socket_t evsignal, short old, short events, void *p)
 {
 	struct evsig_info *sig = &base->sig;
-	(void)p;
+	int sa_flags = *(int *)p;
 
 	EVUTIL_ASSERT(evsignal >= 0 && evsignal < NSIG);
 
@@ -299,7 +300,7 @@ evsig_add(struct event_base *base, evutil_socket_t evsignal, short old, short ev
 	EVSIGBASE_UNLOCK();
 
 	event_debug(("%s: %d: changing signal handler", __func__, (int)evsignal));
-	if (evsig_set_handler_(base, (int)evsignal, evsig_handler) == -1) {
+	if (evsig_set_handler_(base, (int)evsignal, evsig_handler, sa_flags) == -1) {
 		goto err;
 	}