[MAPSERVER-USERS] thread safety

[rich.fromm]

rich.fromm wrote:
> 
> Small scale individual tests work fine.  When I try executing larger
> scale stress tests that include multiple concurrent requests to tomcat,
> things
> run fine for a while, but eventually the JVM crashes and tomcat dies.
> <...>
> I have not yet been able to
> reproduce a single failure -- I'm still working on it.  But if this is a
> threading issue, I may not be able to get a reproducible test case.
> 

I was on the verge of completely blaming threading, but now I'm not so sure.
I have had two more crashes, see #5 and #6 below.  (#1 through #4 are in the
original mail.)  #5 looks to be identical to #3 and #4.  And all of #1
through
#5 occurred when tomcat was potentially handling multiple concurrent
requests.  In no case have I been able to reproduce the exact failure, even
when playing back requests that I think were the trigger of the failure.
Which seems to point to a threading problem.

But in crash #6, I had the client waiting until a request returned before
making another request.  So tomcat was invoking mapserver purely
sequentially,
and I would have thought that threading problems were not an issue.
Nevertheless, eventually the server crashed, and once again if I replay the
exact request that triggered the failure, I can not reproduce the crash.

So I fear that it's going to be very hard for me to create a reproduceable
test case for this, but inevitably if I throw enough requests at mapserver,
it
always crashes and brings down tomcat, usually within about an hour or two.

- Rich

---
crash #5:

(msFreeLabelCacheSlot) mapfile.c:4068
(msFreeLabelCache) mapfile.c:4100
(msFreeMap) mapobject.c:98
(delete_mapObj) mapscript/java/mapscript_wrap.c:1619
(Java_edu_umn_gis_mapscript_mapscriptJNI_delete_1mapObj)
mapscript/java/mapscript_wrap.c:19695

crash #6:

(msImageCreateWithPaletteGD) mapgd.c:3471
(msSaveImageBufferGD) mapgd.c:3697
(msSaveImageBufferAGG) mapagg.cpp:2248
(msSaveImageBuffer) maputil.c:688
(imageObj_getBytes) mapscript/java/mapscript_wrap.c:2486
(Java_edu_umn_gis_mapscript_mapscriptJNI_imageObj_1getBytes)
mapscript/java/mapscript_wrap.c:24414

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