--- On Sun, 10/19/08, Roger Haase <[EMAIL PROTECTED]> wrote:
> From: Roger Haase <[EMAIL PROTECTED]>
> Subject: MiddleKit Threading Error?
> To: webware-discuss@lists.sourceforge.net
> Date: Sunday, October 19, 2008, 3:46 PM
> I last reported this problem back on May 22, 2004. I am not
> sure what I have been doing different lately, but I have
> encountered the problem on both my test system and my
> production system this past month. I have never been able
> to reproduce this problem at will. The problem last went
> away with some 0.8x or 0.9x release but has now occurred on
> 1.0RC1.
>
> I think the problem is caused by:
> 1. a freshly started AppServer
> 2. a flurry of incoming transactions all trying to access
> a MySQL
> table that has not been accessed before.
>
> I think I am hitting the problem because my application
> generates web pages with multiple embedded images that are
> served by the Webware application. So accessing a web page
> may create a flurry of transactions, the first has to wait
> for a disk read, and the second transactions overruns it
> resulting in duplicate entries in the cache.
>
> The abend occurs in MiddleKit/Run/MiddleObject in
> readStoreData at line 92:
> assert len(cache) + 1 == len(row)
>
> Per the fancy traceback, cache is equal to:
> [<unbound method Folder.setFileName>,
> <unbound method Folder.setSurveyDate>,
> <unbound method Folder.setLockUserId>,
> <unbound method Folder.setPhotographer>,
> <unbound method Folder.setComments>,
> <unbound method Folder.setRootId>,
> <unbound method Folder.setSiteId>,
> <unbound method Folder.setNumberFiles>,
> <unbound method Folder.setUpdatedBy>,
> <unbound method Folder.setUpdateTime>,
> -- the problem is here, the fields repeat
> <unbound method Folder.setFileName>,
> <unbound method Folder.setSurveyDate>,
> <unbound method Folder.setLockUserId>,
> <unbound method Folder.setPhotographer>,
> <unbound method Folder.setComments>,
> <unbound method Folder.setRootId>,
> <unbound method Folder.setSiteId>,
> <unbound method Folder.setNumberFiles>,
> <unbound method Folder.setUpdatedBy>,
> <unbound method Folder.setUpdateTime>]
>
> And row is equal to:
> (96L,
> 'MonumentNashRuin_AR-03-09-02-08',
> datetime.date(2007, 2, 6),
> 2L,
> 'RH, GH',
> '',
> 8L,
> 94L,
> 42L,
> 2L,
> datetime.datetime(2007, 9, 18, 12, 44, 3))
>
> I think the solution is to insert a lock around the code
> that deals
> with loading the cache the first time a table is accessed.
> This is my diff from MiddleKit/Run/MiddleObject.py (probably
> hard to read because of the line wraps).
>
Well, the previous solution worked for the failing transaction, but then I hit
another problem on a flurry of 5 transactions that were generating PNG images.
The new problem occurred in the same area - MiddleKit/Run/MiddleObject.py
method readStoreData on the line:
assert 0, "attempted to refresh changed object ....
My revised solution is to put the lock at the beginning and end of the method.
--- C:\...\MiddleObject.py-revBASE.svn005.tmp.py Tue Oct 21 08:41:35 2008
+++ C:...\MiddleObject.py Tue Oct 21 08:36:16 2008
@@ -5,6 +5,9 @@
from MiddleKit.Core.ObjRefAttr import ObjRefAttr
from MiddleKit.Core.ListAttr import ListAttr
+import thread # 2002-08-21 rdh
+_cacheLock = thread.allocate_lock() # 2002-08-21 rdh
+
try: # for Python < 2.2
object
except NameError:
@@ -67,6 +70,7 @@
for the same object in order to "refresh the attributes"
from the persistent store.
"""
+ _cacheLock.acquire() # 2008-10-20 rdh
if self._mk_store:
assert self._mk_store is store, 'Cannot refresh data
from a different store.'
if self._mk_changed and not self._mk_initing:
@@ -114,6 +118,7 @@
self._mk_initing = 0
self._mk_inStore = 1
self._mk_changed = 0 # setting the values above will have
caused this to be set; clear it now.
+ _cacheLock.release() # 2008-10-20 rdh
return self
Roger Haase
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