back off locking contention on sql queues when they are nearly full to allow the…

back off locking contention on sql queues when they are nearly full to allow the system to recover from an attack

src/switch_core_sqldb.c

@@ -1699,6 +1699,9 @@ SWITCH_DECLARE(switch_status_t) switch_sql_queue_manager_destroy(switch_sql_queu
 
 SWITCH_DECLARE(switch_status_t) switch_sql_queue_manager_push(switch_sql_queue_manager_t *qm, const char *sql, uint32_t pos, switch_bool_t dup)
 {
+	char *sqlptr = NULL;
+	switch_status_t status;
+	int x = 0;
 
 	if (sql_manager.paused || qm->thread_running != 1) {
 		switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG1, "DROP [%s]\n", sql);
@@ -1716,10 +1719,20 @@ SWITCH_DECLARE(switch_status_t) switch_sql_queue_manager_push(switch_sql_queue_m
 		pos = 0;
 	}
 
-	switch_mutex_lock(qm->mutex);
-	switch_queue_push(qm->sql_queue[pos], dup ? strdup(sql) : (char *)sql);
-	switch_mutex_unlock(qm->mutex);
+	sqlptr = dup ? strdup(sql) : (char *)sql;
 
+	do {
+		switch_mutex_lock(qm->mutex);
+		status = switch_queue_trypush(qm->sql_queue[pos], sqlptr);
+		switch_mutex_unlock(qm->mutex);
+		if (status != SWITCH_STATUS_SUCCESS) {
+			switch_log_printf(SWITCH_CHANNEL_LOG, SWITCH_LOG_DEBUG1, "Delay %d sending sql\n", x);
+			if (x++) {
+				switch_yield(1000000 * x);
+			}
+		}
+	} while(status != SWITCH_STATUS_SUCCESS);
+	
 	qm_wake(qm);
 
 	return SWITCH_STATUS_SUCCESS;