Antwort: Re: [UMN_MAPSERVER-USERS] Bug in msCopy

[Benedikt Rothe]

Hello Umberto

Thank you for yout hint's!

You are right: One should be cautios. But for the moment I have the 
impression
that we seeme to have found a way, which don't raise obvious errors in the 
first 
moment :-)

After the mentioned changes in mapcopy.c the approache 
(TomCat/MapScript/Connection-Pooling/MapCloning) seeme to 
work for us. (Working with Version 4.6)

But:
- We do need some more stress-testing.(We already made automated 
  http-requests from a Java-Programs. But this was definitly not enough 
and 
  not "nasty" enough!)
- New problems could raise, if more or other features from 
mapserver/mapscript
  are used then we actualy do. 
- Memory footprint of the running-tomcat has to be watched!. What about 
the size 
   of the application after 100, 500, 600, 800 ... requests? (I'm not 
quite shure how to do this!
   Watching Java-Programs is difficult because of garbage-collections ...)

Greetings
Benedikt

Umberto Nicoletti <umberto.nicoletti at gmail.com> schrieb am 29.06.2005 
11:03:46:

> On 6/29/05, Benedikt Rothe <umn-ms at hydrotec.de> wrote:
> > 
> > Dear List 
> > 
> > We are using MapScript/Tomcat/Java/OracleSpatial. 
> > 
> > We use mapObj.mapClone() to get a fresh mapObject 
> > in each request without reading the Mapfile. 
> 
> Benedikt,
> I would not do that (tm). In my apps I recreate a fresh mapObj with
> each request  as the overhead is mininum and the benefits high (so
> that the ratio is in favor of this approach).
> Besides this is the only known method to work (as far as I know) and
> this stems from the fact that mapserver was in the beginning (and
> still is, with improvements) a CGI. As you might know cgis are
> processes that are created by the web server to serve a single request
> and then exit, so memory cleanup and thread safety are non-issues for
> them.
> Even in php mapscript php must be used as a cgi (instead of a DSO) to
> make sure that it works.
> 
> > 
> > We detected problems after we activated Connection-Pooling: 
> > Tomcat crashed in mapObj.delete() 
> >
> 
> I would not use connection pooling just because it will not work
> reliably with Java Servlets for the reasons explained above.
> 
> This matter (connection pooling and map cloning) surely requires
> deeper investigation, one of the developers coul step in to give his
> opinion on my statements (which I would sincerely hope were false, but
> fear not). Btw, I seem to recall that the above issues (long lived
> instance against per request instance)  were already discussed on the
> list before.
> 
> Best regards,
> Umberto
> 
> > Hole thing turned out to be a bug in mapcopy.c where 
> > the joins are copied: 
> > -------------------- 
> > MS_COPYSTELEM(numjoins); 
> > 
> > for (i = 0; i < dst->numprocessing; i++) { 
> >    return_value = msCopyJoin(&(dst->joins[i]), &(src->joins[i])); 
> > -------------------- 
> > 
> > This must be changed to 
> > -------------------- 
> > MS_COPYSTELEM(numjoins); 
> > 
> > for (i = 0; i < dst->numjoins; i++) { 
> >    return_value = msCopyJoin(&(dst->joins[i]), &(src->joins[i])); 
> > -------------------- 
> > 
> > There is some other code in mapobject.c, wich didn't 
> > raise any problems for us, but from wich I do think 
> > that array-allocs are missing. 
> > I watched the code an *think* these are are not allocated 
> > anywhere. I hope, there is no misleading hint: 
> > 
> >  ----------------------------
> >  // I do think, that dst->point is not allocated.
> >  // code seems to be unused (?)
> >  dst->numpoints = src->numpoints;
> >  for (i = 0; i < dst->numpoints; i++) {
> >   MS_COPYPOINT(&(dst->point[i]), &(src->point[i]));
> >  }
> >  ----------------------------
> >  // I do think, that dst->items and dst->values is
> >  // not allocated
> >  MS_COPYSTELEM(numitems);
> >  for (i = 0; i < dst->numitems; i++) {
> >   MS_COPYSTRING(dst->items[i], src->items[i]);
> >   MS_COPYSTRING(dst->values[i], src->values[i]);
> >  }
> > 
> >  -----------------------------
> >  // I'm quite shure, that dst->items is not allocated
> >  MS_COPYSTELEM(numitems);
> > 
> >  for (i = 0; i < dst->numitems; i++) {
> >   MS_COPYSTRING(dst->items[i], src->items[i]);
> >  }
> > 
> > I hope this is helpful. Greetings 
> > Benedikt Rothe
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