Using the ATTACH macro

Figure 1 illustrates the concept of performing an OS ATTACH to a C, C++, nonmultitasking PL/I, or COBOL program, and thus establishing a separate Language Environment runtime environment. For each ATTACH to a Language Environment-conforming routine, another Language Environment runtime environment is added to the MVS™ address space. In COBOL, this is called multitasking; COBOL RES multitasking is supported only when all of the COBOL programs are compiled with Enterprise COBOL for z/OS, COBOL for OS/390 & VM, COBOL for MVS & VM, or COBOL/370 (not with OS/VS COBOL or VS COBOL II).

Figure 1. Issuing an ATTACH to Language Environment-conforming routines

A root HLL routine is created when subtasks in an HLL are attached to an assembler routine.

When running with POSIX(ON), use the POSIX function pthread_create in place of OS ATTACH to create a new thread.

Currently, each Language Environment environment supports one process. Within the process each enclave supports a single thread.

To make best use of the ATTACH macro, you need to be aware of:

Whether you are using POSIX(ON) in a multithread environment. You must not use the ATTACH macro in this case. If you are running a PL/I multitasking application, you cannot use the ATTACH macro.
Whether the Language Environment environments share any resources.
The MVS affinity aspects of each routine. For example, if you OPEN a file in one TCB, you must CLOSE it in the same TCB.
The concurrency aspects of each routine. For example, you must ensure that two routines do not attempt to make contradictory or destructive changes to a data base.
The termination order of all routines, particularly those in a new Language Environment environment.
The compiler options and link-edit options when using COBOL.