topic Re: File Monitoring Service in Operating System - OpenVMS

File Monitoring Service

Robert Cermack — Thu, 12 May 2005 11:39:21 GMT

I'm trying to monitor the existence of a flat file resident on a Unix server from a VMS machine. Currently have a NFS mount giving visibility to the Unix box, but need to develop a VMS (detached?) service to watch for the appearance of the files on the Unix box so they can processed into a database on the VMS machine. I'm not a VMS programmer, so I'm looking for suggestions for available system services, library routines, freeware, etc... to help. Any suggestion ?????

Re: File Monitoring Service

Karl Rohwedder — Fri, 13 May 2005 00:20:43 GMT

A simple (but not very elegant) solution is just have a DIR/FTP in a loop and check the status. This is of course not useful, if you have to check very often...

regards Kalle

Re: File Monitoring Service

Volker Halle — Fri, 13 May 2005 01:02:49 GMT

Robert,

if I understand your references to 'NFS mount' correctly, you have the directory on the Unix box mounted via NFS from the OpenVMS system, so you could see the file from OpenVMS system with a $ DIRECTORY command ?

If so, you could use a simple DCL procedure using F$SEARCH to 'wait' for the appearance of the file and then start processing it:

$loop:
$ file = F$SEARCH("X.X")
$ IF file .nes. "" THEN $ GOTO process_file
$ WAIT 0:0:5
$ GOTO loop
$!
$process_file:
$ SHOW SYMB file

Volker.

Re: File Monitoring Service

Bojan Nemec — Fri, 13 May 2005 01:25:42 GMT

Robert,

I agree with Volker that this is the simplier way. You could submit such procedure in a batch queue to get a "detached" process (I put detached in quotes because this is not a real detached process).

If you want to go on the hard way, there is the VMS documentation:

http://h71000.www7.hp.com/doc/os82_index.html

For system services:
http://h71000.www7.hp.com/doc/82FINAL/4527/4527PRO.HTML
for library routines:
http://h71000.www7.hp.com/doc/82final/5932/5932PRO.HTML

probably you will need RMS:
http://h71000.www7.hp.com/doc/73final/6027/6027PRO.HTML

For the freeware look at:
http://h71000.www7.hp.com/openvms/freeware/index.html

Bojan

Re: File Monitoring Service

David B Sneddon — Fri, 13 May 2005 01:37:03 GMT

Robert,

A slight variation on Volker's procedure...
Depending on the size of the file, it may exist
but still be in the process of being written.
Try opening it for write access, if it fails
go back to waiting.

$loop:
$ file = F$SEARCH("X.X")
$ IF file .nes. "" THEN $ GOTO process_file
$wait_a_bit:
$ WAIT 0:0:5
$ GOTO loop
$!
$process_file:
$ close/nolog channel
$ open/read/write/error=wait_a_bit channel 'file'
$ close/nolog channel
$ SHOW SYMB file

Dave

Re: File Monitoring Service

Jan van den Ende — Fri, 13 May 2005 04:06:23 GMT

Robert,

I agree with David that you should check for the file being closed already.
However, I do not fully trust in NOT being able to write to a _UNIX_ file while it is open. Also, the chance exists that _YOUR_ test-OPEN interferes with the writing app.

Can you have/get any control over the applic that _WRITES_ the file?
My usual approach is to have the generating applic rename the file after closing.
Then checking for the renamed file results in a found file being fullt available for you.

Proost.

Have one on me.

jpe

Re: File Monitoring Service

Robert Cermack — Fri, 13 May 2005 09:01:05 GMT

Thanks to all for your responses. I'll probably work with the DCL (F$SEARCH) batch routine option first and investigate the more robust RMS solution later.

Re: File Monitoring Service

Robert Cermack — Fri, 13 May 2005 09:03:13 GMT

Closed. Thanks again.