Posted by Jim Michaels on 02/12/06 10:08

"Erwin Moller"
<since_humans_read_this_I_am_spammed_too_much@spamyourself.com> wrote in
message news:43eafbbf$0$11061$e4fe514c@news.xs4all.nl...
>a wrote:
>
>> I already posted on this subject, but I have some more information that
>> should make the issue clearer.
>>
>> Config: Apache 2.x, PHP 5.1.x, Windows XP Pro
>>
>> A php script processes a form. Inside this script I call exec to run a
>> Windows process. If I press the submit button on the form repeatedly,
>> exec
>> starts and exit the process several times, but after 2-3 cycles, it
>> starts
>> the process, the process exits, but exec doesn't return, and it hangs the
>> script and the session forever - it won't even timeout.
>
> Hi,
>
> No timeout?
> That sucks.
> Maybe it has to do with multiple requests having the same sessionid
> (PHPSESSID).
>
> If you have a default install, you'll have filebased sessionstorage, and
> just the default sessionhandlingfunctions (No databasesessionstorage or
> own
> functions).
>
> I am not sure if this will help you solve the problem, but here is some
> backgroundinformation:
>
> I am unsure how things are implemented under Win XP, but under *nix the
> following happens:
> 1) Request 1 (carrying some PHPSESSID) arives at the server.
> 2) Server tries to open AND LOCK (flock()) the sessionfile to load the
> sessiondata into the scriptenvironment.
> 3) Script terminates, and the (possibly changed) sessiondata is written to
> the file.

XP is nothing like UNIX except for its POSIX subsystem. But I suppose the
process here is somewhat similar.

>
> This process repeats itself.
> If however a request arives at the server that carries a sessionid of a
> file
> that is already open (LOCKED), this requests WAITS untill the file gets
> unlocked.
> In this way you prevent multiple request to corrupt the sessionfile by
> simultanious writes to the same file, possibly all with other data.
>
> I suspect that you somehow leave the sessionfile locked with your
> systemcall
> that is not returning.
> You can check this by:
> 1) determining the sessionid (Just ask your browser for the value of
> PHPSESID)
> 2) Look up the corresponding file (in some temp-directory as mentioned in
> php.ini)
> 3) Try to open and write to this file, by hand.
>
> If it is locked, you will not be able to.
>
> This is a *nix story.
> BUT, I am unsure how things work on XP. :-(
>
> Hope this helps you getting started with debugging.
> Sessionrelated problems tend to be hard to debug because most of the
> action
> go on before the script start, and after the script finishes.
>
> Regards,
> Erwin Moller
>
>>
>> I tried to block multiple POSTs by using a global var:
>>
>> if( isset( $_SESSION[ "processing" ] ) )
>> {
>> // 1
>> exit;
>> }
>> else
>> {
>> $_SESSION[ "processing" ] = true;
>> exec( ...);
>> unset( _SESSION[ "processing" ] );
>> }
>>
>> but the script never reaches //1.
>>
>> I am totally confused by this reentrancy issue and I don't know how to
>> handle:
>> 1. multiple posts while the script is still running, to avoid hanging the
>> session
>> 2. offering the ability to cancel the processing, if the process takes a
>> long time.
>>
>> One of the requirements is that all processing happen on the server, so
>> no
>> JavaScript is allowed.
>>
>> A related question - can multiple php scripts run simultaneously in the
>> same session -if a user presses submit multiple times, does this run new
>> instance of the script for each POST?
>>
>> I would really appreciate any help.
>>
>> Thanks,
>>
>> A
>

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