COBOL Manual for TNS and TNS/R Programs

HP COBOL Manual for TNS and TNS/R Programs—522555-006
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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.