The concurrent server is complicated to implement. Logic must be split into a main program and a child program. In addition, you have to manage all processes within your application.

In the MVS™ environment, you implement such logic by means of the UNIX fork() call. Because this call is not available in a traditional MVS environment, you must improvise.

In the UNIX environment, the fork function is implemented using APPC/MVS to schedule and initiate a child process in an MVS address space other than the address space of the original process.

If you want to implement a high-performance server application that creates or accesses MVS resource of various kinds (especially MVS data sets), you will probably implement your server as a concurrent server in an MVS address space. This address space can be TSO, batch, or started task.

To implement concurrence in an MVS address space, use MVS multitasking facilities. This limits available programming interfaces to the sockets extended assembler macro programming interface or to C sockets.

For the sockets extended assembler macro interface, use standard MVS subtasking facilities: ATTACH and DETACH assembler macros.

For C sockets, use the subtasking facilities that are part of the IBM® implementation of C in an MVS environment.

The following topics show sockets extended assembler macro examples to illustrate the implementation of a concurrent server in an MVS address space environment.