Preparing COBOL programs for multithreading

You can run COBOL programs in multiple threads within a process under batch, TSO, IMS, or z/OS® UNIX.

There is no explicit COBOL language to use for multithreaded execution; rather, you compile with the THREAD compiler option.

COBOL does not directly support managing program threads. However, you can run COBOL programs that you compile with the THREAD compiler option in multithreaded application servers, in applications that use a C/C++ driver program to create the threads, in programs that interoperate with Java™ and use Java threads, and in applications that use PL/I tasking. In other words, other programs can call COBOL programs in such a way that the COBOL programs run in multiple threads within a process or as multiple program invocation instances within a thread. Your threaded application must run within a single Language Environment® enclave.

Choosing LOCAL-STORAGE or WORKING-STORAGE: Because you must code your multithreaded programs as recursive, the persistence of data is that of any recursive program:

  • Data items in the LOCAL-STORAGE SECTION are automatically allocated for each instance of a program invocation. When a program runs in multiple threads simultaneously, each invocation has a separate copy of LOCAL-STORAGE data.
  • Data items in the WORKING-STORAGE SECTION are allocated once for each program and are thus available in their last-used state to all invocations of the program.

For the data that you want to isolate to an individual program invocation instance, define the data in the LOCAL-STORAGE SECTION. In general, this choice is appropriate for working data in threaded programs. If you define data in WORKING-STORAGE and your program changes the contents of the data, you must take one of the following actions:

  • Structure your application so that you do not access data in WORKING-STORAGE simultaneously from multiple threads.
  • If you do access data simultaneously from separate threads, write appropriate serialization code.

Related concepts  

Related references  
PROGRAM-ID paragraph (Enterprise COBOL for z/OS Language Reference)