[Zodb-checkins] CVS: Zope3/src/zodb/storage - bdbminimal.py:1.4

Barry Warsaw barry@wooz.org
Tue, 31 Dec 2002 12:12:28 -0500

Update of /cvs-repository/Zope3/src/zodb/storage
In directory cvs.zope.org:/tmp/cvs-serv26107

Modified Files:
Log Message:
__collect_objs(): Never collect the root object.

_dopack(): Added an XXX about a potential race conditional that I need
to fix.  I want to try to write a test case for that first, although
it'll be a little tricky.

=== Zope3/src/zodb/storage/bdbminimal.py 1.3 => 1.4 ===
--- Zope3/src/zodb/storage/bdbminimal.py:1.3	Mon Dec 30 17:38:52 2002
+++ Zope3/src/zodb/storage/bdbminimal.py	Tue Dec 31 12:12:27 2002
@@ -370,6 +370,16 @@
         self.log('classic pack finished')
     def _dopack(self):
+        # XXX There is a potential race condition here that we need to address
+        # so we don't lose objects.  Say we've just completed the mark phase
+        # and another thread comes along and stores an object.  Now we enter
+        # the sweep phase and notice that that other object isn't in the
+        # marked list.  So we add it to the collection list.  Full is less
+        # vulnerable to this hole (although it's still there) because it
+        # usually won't pack all the way to the current time.  I want to try
+        # to write a test case for this situation before I fix it, but that's
+        # difficult without instrumenting _dopack() for testing.
+        #
         # Do a mark and sweep for garbage collection.  Calculate the set of
         # objects reachable from the root.  Anything else is a candidate for
         # having all their revisions packed away.  The set of reachable
@@ -455,6 +465,10 @@
             if self._stop:
                 raise PackStop, 'stopped in _collect_objs()'
             oid = orec[1]
+            # Never pack away the root object.
+            if oid == ZERO:
+                orec = self._oidqueue.consume(txn)
+                continue
             # Delete the object from the serials table
             c = self._serials.cursor(txn)