topic Re: What is process? in Operating System - OpenVMS

What is process?

Sathyaswarupa — Tue, 07 Feb 2006 04:10:32 GMT

Hi Gurus!

I'm now finding myself locked in this concept of process? What is it? Why is it so important in OpenVMS?
When do we need interprocess synchronization?
How to do that?

please do Guide me on this.

With respects

Re: What is process?

Wim Van den Wyngaert — Tue, 07 Feb 2006 04:42:00 GMT

This might explain it in general.

http://www.eas.asu.edu/~cse430a/lectures/14

You need interprocess sync when 2 programs need to sync there actrivity. E.g. block db activity until a database writer process has completed a checkpoint.

Wim

Re: What is process?

faris_3 — Tue, 07 Feb 2006 04:44:03 GMT

A process is an environment created by the OpenVMS operating system that lets you interact with the system. This chapter describes:

Interpreting your process context
Using subprocesses
Connecting to disconnected processes on virtual terminals
Working with batch jobs

What is different on VMS from other systems
is that a process can execute a series of different programs.

See chapter 18 of this documentation for an introduction :
http://h71000.www7.hp.com/doc/73final/6489/6489pro_047.html#bottom_047

Hth
/hf

Re: What is process?

Ian Miller. — Tue, 07 Feb 2006 06:22:49 GMT

Re: What is process?

Jan van den Ende — Wed, 08 Feb 2006 04:51:59 GMT

Sathyaswarupa,

from your Forum Profile:

I have assigned points to 19 of 44 responses to my questions.

Maybe you can find some time to do some assigning?

http://forums1.itrc.hp.com/service/forums/helptips.do?#33

Mind, I do NOT say you necessarily need to give lots of points. It is fully up to _YOU_ to decide how many. If you consider an answer is not deserving any points, you can also assign 0 ( = zero ) points, and then that answer will no longer be counted as unassigned.
Consider, that every poster took at least the trouble of posting for you!

To easily find your streams with unassigned points, click your own name somewhere.
This will bring up your profile.
Near the bottom of that page, under the caption "My Question(s)" you will find "questions or topics with unassigned points " Clicking that will give all, and only, your questions that still have unassigned postings.

Thanks on behalf of your Forum colleagues.

PS. - nothing personal in this. I try to post it to everyone with this kind of assignment ratio in this forum. If you have received a posting like this before - please do not take offence - none is intended!

Proost.

Have one on me.

jpe

Re: What is process?

Arch_Muthiah — Wed, 08 Feb 2006 15:19:23 GMT

Sathya,

We DOS is Single user OS, VMS is multiuser OS.
Each USER in VMS can have many Processes and Sub-Processes.
Each of those processes can do USER's job.
Each Job is a group of small Tasks.

Though VMS can allow thousands thousands of USER's processes, but few process only can access the CPU in the round-robin method (sitting in the queue). Some time high privileged user's high priority process can jumped into the queue to access the CPU.

Once a process completes its tasks, then it will move out of the queue (COMputed queue) and leaves work place for the next process on the basis of privilege, priority an also the order they entered the system.

When a user logged into the system, VMS creates a process first default process for that user to do his job. He can create many process and subprocess using VMS system's built-in services (functions).

There are services and event flags in VMS using which a user can make his processes to communicate each other processes, he can make his process's task to communicate with other tasks (communications within a process, communications between the process, task-to-task communications)

These process's and tasks communications can be used to transfer the data and informations within one VMS system, and networked VMS systems.

These communications can be made possible by setting/clearing the EVENT Flags in communication/datatransfer/mailbox related system services, sys$synchronise, sys$schedwakeup, sys$hangxxx, sys$settimer, etc.,...

As we know in Oracle, there background process which actually carry out the user's request. Those are like user's agent which will get or (wait for) user's request, and returns the result back to the user, but these are automatically created for the user. But in VMS, along with VMS system created AUTOmatic process, we can also create a seperate process/subprocess and can give our job to that particular process.

Comming to your specific question, in VMS there are EVENT flags to be used within the process and there are common event flags for use interprocess communications, MAILBOX mechanism to process communications, and SYS$xxxx services (mentioned above) to do process-to-process and task-to-task communications.

If you have any specific questions deep in this area, you can get clear from THIS great VMS forum's excellent members.

Archunan