A program, whether in supervisor state or problem state, can use the ALCOPY=YES parameter on the ATTACH or ATTACHX macro to attach a subtask and pass a copy of its DU-AL to this subtask. In this way, the program can share data spaces or hiperspaces with a program running under the subtask. The two programs both have access to the address/data spaces and hiperspaces that have DU-AL entries at the time of the ATTACH or ATTACHX macro invocation. Note that it is not possible to pass only a part of the DU-AL.

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.

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

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

Figure 1. Two programs sharing a SCOPE=SINGLE data space

Example of Attaching a Task and Passing a DU-AL

   DSPSERV CREATE,NAME=DSNAME,BLOCKS=DSSIZE,STOKEN=DSSTOK,ORIGIN=DSORG
   ALESERV ADD,STOKEN=DSSTOK,ALET=DSALET
   ATTACHX EP=PGM2,ALCOPY=YES
  .
DSNAME      DC   CL8'MYDSPACE'   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 two DU-ALs do not necessarily stay identical; after the attach, PGM1 and PGM2 are free to add and delete entries on their own DU-ALs.

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