Developing Applications for Use with UNIX System Services OS/390

Processes

In the USS shell environment, a running program is called a process. Multiple processes can be executed independently of each other, with each process receiving its own address space. To facilitate the referencing of these independent processes, each process is associated with a process identification number (PID).

A process can be used to start other processes. The USS shell is a process itself that can be used to start multiple processes. At any one time, the shell can have one process running in the foreground and several processes running in the background. A foreground process ties up the shell and prevents you from entering additional commands while it is running. The shell does not wait for the completion of background processes; they run in the background in a manner similar to an OS/390 batch job. The ps shell command can be used to display the PID for the shell and all of the processes running under the shell.

Processes can also be started by SAS/C programs. The exec family of functions and the fork and atfork functions are commonly used to start a new process. The SAS/C extension function oeattach can be used to start a new process in the same address space as the old process, which may offer improved performance over the use of fork and exec . Refer to the SAS/C Library Reference, Volume 2 for more information about these functions.

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