Re: Question on QTEMP and CGI Jobs

[Scott Klement <web400@xxxxxxxxxxxxxxxx>]

Richard,

I agree with what everyone else has said, Apache never uses the same job 
two run two CGI requests concurrently via threads.

It does have the capability to start CGI jobs as "multiple thread 
capable" (there's an Apache directive to enable this).  But, this only 
marks the job as capable of multiple threads so that the CGI job can 
internally spawn threads if it desires.  Apache does not call it in a 
multiple concurrent thread manner.

Are you "absolutely" sure that the programmer isn't confusing a request 
(or a "call" as you've phrased it) with a session?  Because within the 
scope of a session, it's very possible (and likely) that other sessions 
will also be serviced by the same job with the same QTEMP. And 
conversely, it is also true that a single session will be handled by 
multiple jobs with different QTEMPs.

This is a very common mistake that people make.  And, it can be hard to 
detect during testing, because frequently the load on the test HTTP 
server isn't very high, so it may come back with the same job for all 
requests in the session just by "luck."   But in production server where 
there are more requests, it'll almost certainly switch jobs during a 
session, and re-use the same job for other sessions.

In fact, if your programmer does in fact understand the difference 
between requests and sessions and knows that the QTEMP is used in a 
valid manner (i.e. only during the space of a single REQUEST) then I'm 
having a hard time even understanding what value QTEMP provides?  Since 
the data can only reside there (legimately, anyway) for a very small 
time, and you can't use it to keep data persistent within the session, 
what purpose does it serve to use QTEMP?   Something like an *OUTFILE 
option that you're going to immediately process and then delete would be 
one legitimate use... but that's about it.

Of course, if we're talking about persistent CGI, that's a different 
story...

-SK


On 3/4/17 12:33 PM, Richard Schoen wrote:
> I was chatting offline with someone else here from the list and this
> has brought up the following follow on question in my head:
>
> Are we "absolutely" sure that each individual synchronous CGI call
> through the Apache server gets serviced by a separate single job
> instance and not potentially by multiple threads within a single CGI
> job instance ?
>
> If the latter condition occurs within the modern Apache Server then
> the argument NOT to use QTEMP is very valid because two threads in
> the same job would have access to the same QTEMP instance.
>
> Regards,
>
>
> Richard Schoen
> Director of Document Management
> e. richard.schoen@xxxxxxxxxxxxxxx
> p. 952.486.6802
> w. helpsystems.com