COBOL Manual for TNS/E Programs (H06.08+, J06.03+)

31 Process Initiation, Communication, and Management
On a NonStop system, a process is a running program. More specifically, it is the unique executing
entity created when someone runs object code from a loadfile in one of these ways:
• By entering an explicit RUN command (for example, RUN COBOL85)
• By entering an implicit RUN command (for example, COBOL85)
• By calling the PROCESS_CREATE_ procedure from another process
If a user runs two separate programs, the operating environment creates two processes. The
operating environment also creates two processes if the user runs two instances of the same program
concurrently, or if two users run the same program concurrently.
Physically, each process consists of at least:
• A shareable, unmodifiable code area containing instructions and constants
• An exclusive, modifiable data area called a stack
• An exclusive entry in the process control block (PCB), a system table that uniquely defines the
process within the system
This arrangement permits two users of the same loadfile to use only one code area. Although two
processes can share a code area, each process has its own data area and PCB.
Although several processes in a particular processor module can share resources and attempt to
run, only one process actually executes in a given processor module at a given instant. Actual
process execution requires the use of the processor’s hardware registers, which are allocated to
the running process by the operating environment. Before the running process yields the processor
module to another process or to an interrupt handler, the operating environment saves information
about the current executing environment in the process’s PCB entry. This strategy permits the
operating environment to restore that environment when the process resumes execution.
A process comes into being when the operating environment takes the code and data produced
by compilation and either binding or linking and combines them with the memory and other
resources of the computer system. The process exists until it requests termination (or is terminated)
and surrenders its resources.
Figure 39 Process Creation, Execution, and Termination
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