Re: HTTP API or Web Service concurrency issue

We've run into that before. Developers on other platforms in our company had trouble believing it.
One had said they "We had to add seconds to the timestamp to avoid dupes". Wow!

I have a few processes where we've appended a sequence # to the timestamp within a job for uniqueness.

Roger Harman
COMMON Certified Application Developer - ILE RPG on IBM i on Power




 

 



From: RPG400-L <rpg400-l-bounces@xxxxxxxxxxxxxxxxxx> on behalf of Mike Jones <mike.jones.sysdev@xxxxxxxxx>
Sent: Friday, May 31, 2019 4:52 PM
To: RPG programming on IBM i
Subject: Re: HTTP API or Web Service concurrency issue
 
Hi Charles,

Thanks for that temp file API tip.  I'll be using it.

I wrote a simple program obtaining a timestamp, and recording it into a
file.  I simultaneously ran two instances of that program, and was able to
reproduce the capture of identical timestamps.  Apparently, the developer
had wishful thinking that a timestamp precision of 6 fractional seconds
would be unique.

Each copy of the test program wrote 500,000 timestamps to a file, for a
total of 1,000,000, and to my surprise, a healthy volume of 2,687 duplicate
timestamps were captured.

I'm glad this is the problem, because the fix is an easy one.

Scott + Charles + Nathan -> have a great weekend and thank you again for
your help.

Mike

On Fri, May 31, 2019 at 4:06 PM Charles Wilt <charles.wilt@xxxxxxxxx> wrote:

On Fri, May 31, 2019 at 2:54 PM Mike Jones <mike.jones.sysdev@xxxxxxxxx>
wrote:

In step a.1, the IFS output file created contains a timestamp in the file
name, with a precision of 6 fractional seconds.  That should do a very

good

job ensuring a unique file name, but I see that as a potential problem
where 2 jobs could, in theory, obtain the same exact timestamp, and

collide

on the IFS output file name.  I'll likely recommend shoring that up to
ensure uniqueness.

Yeah...that could be a problem...

Take a look at the tmpfile() — Create Temporary File API
https://www.ibm.com/support/knowledgecenter/ssw_ibm_i_72/rtref/tempfile.htm
IIRC, HTTP API even makes use of it...

Charles
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