IBM OS/390 manual Multitasking Macros, ATTACH/DETACH Macros

13.2.2 Multitasking Macros

Under VSE, when you specify asynchronous processing at system generation time, the multitasking group of macros is supported to permit more than one task to execute within each partition. Each subtask must be initiated by the main task: control then passes to the subtask.

The storage protection key and priority of the partition remain the same, but the priority of a task within a partition is determined by the sequence of subtasks it attached. Thus, if subtask 1 through subtask n are attached in ascending order, the priority of execution within the partition would be from subtask 1 to subtaskn, then to the main task.

Under MVS, asynchronous processing is supported. This dynamic parallel structure differs from VSE in that:

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Subtasks may be created by job step tasks or other subtasks.

No absolute rules exist for assigning priorities to tasks and subtasks. When created, subtasks are assigned a priority by the originating task. Within limits, this priority may be higher, lower, or the same as the originating task.

∙Any time during execution, the originating task may modify the priority of an attached subtask (as long as it has the task control block (TCB) address of the subtask).

The VSE multitasking macros can be divided into three general categories:

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Subtask initiation and normal termination macros ATTACH/DETACH.

Resource protection macros RCB/ENQ/DEQ.

Intertask communication macros WAITM/POST.

The MVS counterparts and their comparable features follow.

13.2.2.1 ATTACH/DETACH Macros

VSE	ATTACH	entrypoint(S,entrypoint)(r1)
		,SAVE=savearea(S,savearea)(r2)
		,ABSAVE=savearea1
		(S,savearea)&vbar,(r3)
		,ECB=ecbname(S,ecbname)(r4)
		,MFG=area(S,area)(r5)
		,RETURN=NOYES
		,NAME=(name(S,name(r8))
MVS	ATTACH	EP=symbol		,DCB=dcb address
		EPLOC=address of name		(2-12)
		(2-12)
		DE=address of list entry
		(2-12)
		,LPMOD=number		,DPMOD=number
		(2-12)		(2-12)
		,PARAM=(address	,...)	,VL=1
		(2-12)
		,ECB=ecb address	,ETXR=exit routine
		(2-12)		(2-12)

Chapter 13. A s s e m b l e r 283