int mb_probe( int socket, int msg_id, char *app_name, int sync )
mb_probe asks for the number of processes registered as app_name. socket is a connector returned by a previous call to
mb_bind. msg_id is a request number which can be used to uniquely identify the reply.
If sync is 1, the calling process is blocked until the bus responds and
mb_probe returns the number of processes registered as app_name or -1 if an error occured. Use sync only if you are sure no other messages are waiting to be read.
If sync is 0,
mb_probe immediately returns 0 or -1 in case of error. The reply must be read with