Added simple_mutex_t dcb->mutex to DCB struct to protect processing of single dcb in poll.c:poll_waitevents. This is a coarse locking but seems to work with multiple threads at least with very simple load.

Added trace logging to many locations.

server/include/dcb.h

@@ -20,6 +20,7 @@
 #include <spinlock.h>
 #include <buffer.h>
 #include <gwbitmask.h>
+#include <skygw_utils.h>
 
 struct session;
 struct server;
@@ -133,6 +134,7 @@ typedef struct {
  * gateway may be selected to execute the required actions when a network event occurs.
  */
 typedef struct dcb {
+        simple_mutex_t  mutex;          /**< Protects dcb processing. Coarse and temporary? */
 	int		fd;		/**< The descriptor */
 	int 		state;		/**< Current descriptor state */
 	char		*remote;	/**< Address of remote end */