make register_unref() return NULL so it is easy to cleanup

the original pointer while calling the function.

on passing add some comments on one of the places where it
is used, and explain why it is safe there.

again, a no-op for practical purposes.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@77654 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -1878,10 +1878,11 @@ static void unref_user(struct sip_user *user)
 	ASTOBJ_UNREF(user, sip_destroy_user);
 }
 
-static void registry_unref(struct sip_registry *reg)
+static void *registry_unref(struct sip_registry *reg)
 {
 	ast_debug(3, "SIP Registry %s: refcount now %d\n", reg->hostname, reg->refcount - 1);
 	ASTOBJ_UNREF(reg, sip_registry_destroy);
+	return NULL;
 }
 
 /*! \brief Add object reference to SIP registry */
@@ -3531,7 +3532,7 @@ static void __sip_destroy(struct sip_pvt *p, int lockowner, int lockdialoglist)
 	if (p->registry) {
 		if (p->registry->call == p)
 			p->registry->call = NULL;
-		registry_unref(p->registry);
+		p->registry = registry_unref(p->registry);
 	}
 
 	/* Unlink us from the owner if we have one */
@@ -7994,17 +7995,18 @@ static int sip_reg_timeout(void *data)
 		/* Unlink us, destroy old call.  Locking is not relevant here because all this happens
 		   in the single SIP manager thread. */
 		p = r->call;
-		if (p->registry) {
-			registry_unref(p->registry);
-			p->registry = NULL;
-		}
-		r->call = NULL;
 		p->needdestroy = 1;
 		/* Pretend to ACK anything just in case */
 		__sip_pretend_ack(p); /* XXX we need p locked, not sure we have */
+
+		/* decouple the two objects */
+		/* p->registry == r, so r has 2 refs, and the unref won't take the object away */
+		if (p->registry)
+			p->registry = registry_unref(p->registry);
+		r->call = dialog_unref(r->call);
 	}
 	/* If we have a limit, stop registration and give up */
-	if (global_regattempts_max && (r->regattempts > global_regattempts_max)) {
+	if (global_regattempts_max && r->regattempts > global_regattempts_max) {
 		/* Ok, enough is enough. Don't try any more */
 		/* We could add an external notification here... 
 			steal it from app_voicemail :-) */