[load_balancer] Improve probing by sending the probs outside locking

Collect the data under locking, move the OPTIONs probing outside the locking, to be sure that any potential blocking on SIP level sending is not leading to lock starvation.
Simialar to 4c7a7a8 (drouting)
Related to #2438

modules/load_balancer/lb_prober.c

@@ -35,6 +35,10 @@ extern struct tm_binds lb_tmb;
 void set_dst_state_from_rplcode( int id, int code);
 
 
+typedef struct lb_param_prob_callback {
+	unsigned int  id;
+}lb_param_prob_callback_t;
+
 
 static void lb_probing_callback( struct cell *t, int type,
 		struct tmcb_params *ps )
@@ -45,7 +49,7 @@ static void lb_probing_callback( struct cell *t, int type,
 		LM_CRIT("BUG - reply to a LB probe with no ID (code=%d)\n", ps->code);
 		return;
 	}
-	id = (int)(long)(*ps->param);
+	id = ((lb_param_prob_callback_t*)*ps->param)->id;
 
 	set_dst_state_from_rplcode( id, ps->code);
 
@@ -56,11 +60,25 @@ static void lb_probing_callback( struct cell *t, int type,
 
 void lb_do_probing(struct lb_data *data)
 {
+	struct gw_prob_pack {
+		/* IMPORTANT, this member must be the first, as we use its pointer
+		 * to free the whole structure here */
+		lb_param_prob_callback_t params;
+
+		str uri;
+
+		struct gw_prob_pack *next;
+	};
 	struct lb_dst *dst;
+	struct gw_prob_pack *pack, *pack_last, *pack_head;
 
 	if ( !lb_cluster_shtag_is_active() )
 		return;
 
+	pack_last = pack_head = NULL;
+
+	lock_start_read( ref_lock );
+
 	/* go through all destinations */
 	for( dst = data->dsts ; dst ; dst=dst->next ) {
 		/* dst requires probing ? */
@@ -73,13 +91,41 @@ void lb_do_probing(struct lb_data *data)
 			)
 			continue;
 
-		if (lb_tmb.t_request( &lb_probe_method, &dst->uri, &dst->uri,
+		/* build its pack, so we can build and send the prob later */
+		pack = shm_malloc(sizeof(struct gw_prob_pack)+dst->uri.len);
+		if( pack==0 ) {
+			LM_ERR("no more shm memory!\n");
+			/* send whatever probs we have so far */
+			break;
+		}
+
+		pack->uri.s = (char*)(pack+1);
+		memcpy(pack->uri.s, dst->uri.s, dst->uri.len);
+		pack->uri.len = dst->uri.len;
+
+		pack->params.id = dst->id;
+
+		if (pack_head==NULL) {
+			pack_head = pack_last = pack;
+		} else {
+			pack_last->next = pack;
+			pack_last = pack;
+		}
+
+	}
+
+	lock_stop_read( ref_lock );
+
+	/* now send all the probs, outside the lock */
+	for( pack = pack_head ; pack ; pack=pack->next ) {
+
+		if (lb_tmb.t_request( &lb_probe_method, &pack->uri, &pack->uri,
 		&lb_probe_from, NULL, NULL, NULL, lb_probing_callback,
-		(void*)(long)dst->id, NULL) < 0) {
+		(void*)(long)pack, osips_shm_free) < 0) {
 			LM_ERR("probing failed\n");
+			shm_free(pack);
 		}
 
-
 	}
 
 }

modules/load_balancer/load_balancer.c

@@ -771,14 +771,11 @@ void set_dst_state_from_rplcode( int id, int code)
 
 static void lb_prob_handler(unsigned int ticks, void* param)
 {
-	lock_start_read( ref_lock );
-
 	/* do probing */
 	lb_do_probing(*curr_data);
-
-	lock_stop_read( ref_lock );
 }
 
+
 static void lb_update_max_loads(unsigned int ticks, void *param)
 {
 	struct lb_dst *dst;