[MAPSERVER-USERS] msProcessProjection(): Projection library error.

[Tamas Szekeres]

Frank,

I think this issue might be originated to a missing lock around the
static pj_errno in the proj library. Apparently the 'no system list'
indicates an invalid error code that is: an invalid actual value of
pj_errno. I guess the code below may run against another pj invocation
that is not locked.

Best regards,

Tamas



2008/3/4, Frank Warmerdam <warmerdam at pobox.com>:
> rich.fromm wrote:
>  > I'm not sure if anyone is going to be able to be of any help with this, since
>  > I am not able to consistently reproduce the problem.  Nevertheless, based on
>  > previous instructions, just in case, I am reporting a rare problem seen
>  > under
>  > heavy load.
>  >
>  > I am stress testing a custom webapp using java mapscript.  On several
>  > occasions, I have observed mapserver logging an error, which caused tomcat
>  > to
>  > return a 500 (Internal Server Error), but NOT crash.  The error is as
>  > follows:
>  >
>  > --- begin ---
>  > java.lang.UnknownError: msProcessProjection(): Projection library error. no
>  > system list, errno: 22
>  >
>  >         at edu.umn.gis.mapscript.mapscriptJNI.new_mapObj(Native Method)
>  >         at edu.umn.gis.mapscript.mapObj.<init>(mapObj.java:288)
>  > --- end ---
>
>
> Rich,
>
>  Looking at the code in mapfile.c I see:
>
>
>      msAcquireLock( TLOCK_PROJ );
>      if( !(p->proj = pj_init(numargs, args)) ) {
>          int *pj_errno_ref = pj_get_errno_ref();
>          msReleaseLock( TLOCK_PROJ );
>          msSetError(MS_PROJERR, pj_strerrno(*pj_errno_ref),
>                     "msProcessProjection()");
>          return(-1);
>      }
>
>      msReleaseLock( TLOCK_PROJ );
>
>  I suspect the msReleaseLock( TLOCK_PROJ ) ought to be after the
>  msSetError() instead of before it, though it is also possible this
>  would introduce a deadlock condition if something else that is
>  waiting for the PROJ lock already holds the error lock.  You might
>  want to experiment with this if you are comfortable rebuilding things.
>
>  If this sequence turns out to be the issues there are certainly ways
>  to restructure the code a bit to be safe.
>
>  But this wouldn't explain why you are only occationally getting this
>  error, so I suspect it is a red herring - not your real issue for which
>  I have no useful advice.
>
>  Best regards,
>
> --
>  ---------------------------------------+--------------------------------------
>  I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>  light and sound - activate the windows | http://pobox.com/~warmerdam
>  and watch the world go round - Rush    | President OSGeo, http://osgeo.org
>
>
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