RE: tmpnam() not unique

Thanks Scott.

You say tmpnam() already uses current job number but it is still possible for a collision to occur (with another job) ?


-----Original Message-----
From: RPG400-L [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Hanson
Sent: 14 October 2014 15:40
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: tmpnam() not unique


The code for the IFS version of tmpnam() uses both the current job number and the current clock (timestamp) to generate a unique filename. Once the name is generated, the code uses stat() to make sure a filename does not already exist with that name. If the file already exists, it will generate another name. The name generated by tmpnam() is unique to the system at time of generation.

It is possible for a collision to occur with the filename such that the same filename is generated twice. The caller of the tmpnam() routine should test that some other process has not created an equivalently named file in the lag time between name generation and file creation. Some applications can use the tmpfile() function to avoid this issue.

Your solution of adding the job number as a prefix/suffix should work well and avoid any potential issues.

Scott Hanson

message: 5
date: Tue, 14 Oct 2014 13:19:57 +0000
from: "McGovern, Sean" <Sean.McGovern@xxxxxxxxxxxx>
subject: tmpnam() not unique

I've believe I have encountered an issue with my use of tmpnam().

If 2 jobs use tmpnam() at the same timestamp moment, I *think* the
same filename is returned (though I don't know how to test this

scenario).

I haven't coded to handle this possibility, and end up with two jobs
trying to create the same temporary IFS file.

I was thinking that a solution could be just prefix/suffix the job
number to the filename returned by tmpnam().

Does that seem like a feasible solution ?

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