The following are programming considerations for Exit 56:

• Locating the JCT Control Block Extensions

  You can locate extensions to the job control table ($JCT) control block from this exit using the $JCTXGET macro. For example, you can use these extensions to retrieve job-related information from the $JCTX control block to ship across the network in $NHD macro sections. For more information, see z/OS JES2 Macros.

• Accessing $NITs

  The $NIT macro defines the characteristics of NJE nodes. The $NITs are arranged in a table that is indexed by the node number. The table of $NITs is in JES2 private storage and shadowed in a data space for use outside the JES2 address space. Installation exits can use three fields in the $NJEWORK work area to access the $NIT table. Installation exits can use these fields to access a $NIT without regard for what address space they are in.

  Because these fields are in the $NJEWORK data area, you can address them using the ‘NJE’ prefix or the prefix for the device dependent work area in which the $NJEWORK is embedded. Therefore, you can address NJENITAD as JRWNITAD in the $JRW, JTWNITAD in the $NJT, SRWNITAD in the $SRW, and STWNITAD in the $STW.

  The following code accesses the origin node’s NIT in an NJE JOB receiver exit:

   USING NIT,R1               Est NIT addressability
   SPACE 1
  $ARMODE ON,SYSSTATE=SET,INIT=CCTZEROS Enter AR mode
   SPACE 1
   LLGH  R1,JRWRDNOD          Get origin node number
   MH    R1,CCTNITSZ          Get NIT offset
   AL    R1,JRWNITBL          Get NIT address
   LAM   AR1,AR1,JRWNITAL     Get NIT ALET

• Determining the device type

  Most exits need to determine the type of device that they are being called under. The $NJEWORK area has copies of $DCT fields that can help identify the device. Which method you use depends on the condition that you are testing for.

  The field NJEDEVTP (that corresponds to DCTDEVTP) is a one byte flag that can be used to test for classes of devices. A test of the DCTNET bit in NJEDEVTP indicates that the exit is being called under a networking device. A compare of the byte to DCTINR indicates that the exit is being called under an internal reader. See the $DCT for the meaning of the bits in DCTDEVTP.

  NJEDEVID corresponds to DCTDEVID. This is a 3 byte value that can uniquely identify a device. This is more often used when knowing what specific device you are running under. See the $DCT for the meaning of the fields.