Accessing CKPTed Data Area

If you are running code in one of the user environment exits, you might need to access data that is in the JES2 checkpoint data set. To facilitate this, JES2 maintains a “live checkpoint version” in the checkpoint version data space. This live version is an IARVSERV shared copy of the instorage checkpoint data set. It is updated by the main task as your exit is looking at the data. It is not advisable to run chains in the live version because the chains can be altered by the main task as you run them. However, if you know where a needed data area is located (a JQE or a JOE for example), and the data area is not going away (it is busy on your device), using a live version is a way to obtain the latest checkpoint data.

If you are in a user environment exit working with a NJE/TCP device (that is you are running in a NETSERV address space), the following code accesses an IASDSERV data area that points to the live version (xx in xxWNSST is SR, ST, JR, or JT for the appropriate device dependent area) :

USING DSERV,R5           Est DSERV addressability
SPACE 1
L     R5,xxWNSST         Get NSST address
LAE   R5,0(R5)           Clear access register
L     R5,NSSNSCT-NSST(,R5) Get NSCT address
L     R5,NSCDSERV-NSCT(,R5) Get live DSERV addr

If you are not sure whether or not you are in a NETSERV address space, you can obtain an IAZDSERV for the live version using the $DSERV macro. For example:

$DSERV FUNC=GET,     Get DSERV
       LIVE=YES,     Use “live” version
       DSERV=(R2)     Save address in R2
:
 Code using DSERV in R2
:
$DSERV FUNC=FREE,     Free DSERV
       DSERV=(R2)     Address of DSERV to free