@@ -2134,6 +2134,7 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 	unsigned int hash;

 	ds_set_t *idx = NULL;

 	int ulast = 0;

+	int vlast = 0;

 	if(msg == NULL) {

 		LM_ERR("bad parameters\n");

@@ -2188,8 +2189,11 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 			}

 			break;

 		case DS_ALG_ROUNDROBIN: /* 4 - round robin */

+			lock_get(&idx->lock);

 			hash = idx->last;

 			idx->last = (idx->last + 1) % idx->nr;

+			vlast = idx->last;

+			lock_release(&idx->lock);

 			ulast = 1;

 			break;

 		case DS_ALG_HASHAUTHUSER: /* 5 - hash auth username */

@@ -2200,8 +2204,11 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 					break;

 				case 1:

 					/* No Authorization found: Use round robin */

+					lock_get(&idx->lock);

 					hash = idx->last;

 					idx->last = (idx->last + 1) % idx->nr;

+					vlast = idx->last;

+					lock_release(&idx->lock);

 					ulast = 1;

 					break;

 				default:

@@ -2222,8 +2229,10 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 			hash = 0;

 			break;

 		case DS_ALG_WEIGHT: /* 9 - weight based distribution */

+			lock_get(&idx->lock);

 			hash = idx->wlist[idx->wlast];

 			idx->wlast = (idx->wlast + 1) % 100;

+			lock_release(&idx->lock);

 			break;

 		case DS_ALG_CALLLOAD: /* 10 - call load based distribution */

 			/* only INVITE can start a call */

@@ -2253,8 +2262,10 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 			}

 			break;

 		case DS_ALG_RELWEIGHT: /* 11 - relative weight based distribution */

+			lock_get(&idx->lock);

 			hash = idx->rwlist[idx->rwlast];

 			idx->rwlast = (idx->rwlast + 1) % 100;

+			lock_release(&idx->lock);

 			break;

 		case DS_ALG_PARALLEL: /* 12 - parallel dispatching */

 			hash = 0;

@@ -2304,10 +2315,13 @@ int ds_manage_routes(sip_msg_t *msg, ds_select_state_t *rstate)

 		rstate->emode = 1;

 	}

-	/* update last field for next select to point after the current active used */

-	if(ulast) {

+	/* update last field for next select to point after the current active used,

+	 * if not updated meanwhile */

+	lock_get(&idx->lock);

+	if(ulast && (vlast == idx->last)) {

 		idx->last = (hash + 1) % idx->nr;

 	}

+	lock_release(&idx->lock);

 	LM_DBG("selected [%d-%d-%d/%d] <%.*s>\n", rstate->alg, rstate->setid,

 			rstate->umode, hash,