Sharing data spaces among problem-state programs with PSW key 8-F

Problem-state programs with PSW key 8 - F can share data spaces with other programs in several ways:

A problem-state program with PSW key 8 - F can create a data space and place an entry for the data space on its DU-AL. Then the program can attach a subtask and pass a copy of its DU-AL to this subtask, and pass the ALET. However, no existing task in the job step can use this new ALET value.
A problem-state program with PSW key 8 - F can create a data space, add an entry to the PASN-AL, and pass the ALET to other problem-state programs running under any task in the job step.
A problem-state program with PSW key 8 - F can create a data space and pass the STOKEN to a program in supervisor state. The supervisor-state program can add the entry to either of its access lists.

By attaching a subtask and passing a copy of the DU-AL, a program can share its existing data spaces with a program that runs under the subtask. In this way, the two programs can share the SCOPE=SINGLE data spaces that were represented on the DU-AL at the time of the attach. The ALCOPY=YES parameter on the ATTACH or ATTACHX macro allows a problem-state program to pass a copy of its DU-AL to the subtask the problem-state program is attaching. Passing only a part of the DU-AL is not possible.

A program can use the ETXR option on ATTACH or ATTACHX to specify the address of an end-of-task routine to be given control after the new task is normally or abnormally terminated. The exit routine receives control when the originating task becomes active after the subtask is terminated. The routine runs asynchronously under the originating task. Upon entry, the routine has an empty dispatchable unit access list (DU-AL). To establish addressability to a data space created by the originating task and shared with the terminating subtask, the routine can use the ALESERV macro with the ADD parameter, and specify the STOKEN of the data space.

In the following example, shown in Figure 1, assume that program PGM1 (running under TCBA) has created a SCOPE=SINGLE data space DS1 and established addressability to it. PGM1's DU-AL has several entries on it, including one for DS1. PGM1 uses the ATTACHX macro with the ALCOPY=YES parameter to attach subtask TCBB and pass a copy of its DU-AL to TCBB. It can also pass ALETs in a parameter list to PGM2. Upon return from ATTACHX, PGM1 and PGM2 have access to the same data spaces.

The figure shows the two programs, PGM1 and PGM2, sharing the same data space.

Figure 1. Two Problem Programs Sharing a SCOPE=SINGLE Data Space

An example of the code that attaches TCBB and passes a copy of the DU-AL is as follows:

   DSPSERV CREATE,NAME=DSNAME,BLOCKS=DSSIZE,STOKEN=DSSTOK,            *
                ORIGIN=DSORG
   ALESERV ADD,STOKEN=DSSTOK,ALET=DSALET
   ATTACHX EP=PGM2,ALCOPY=YES
  .
  .
DSNAME      DC   CL8'TEMP    '   DATA SPACE NAME
DSSTOK      DS   CL8             DATA SPACE STOKEN
DSALET      DS   F               DATA SPACE ALET
DSORG       DS   F               ORIGIN RETURNED
DSSIZE      DC   F'2560'         DATA SPACE 10 MEGABYTES IN SIZE

The DU-ALs do not necessarily stay identical. After the attach, PGM1 and PGM2 can add and delete entries on their own DU-ALs; these changes are not made to the other DU-AL.

If TCBA terminates, the system deletes the data space that belonged to TCBA and terminates PGM2.