[Modeling-cvs] ProjectModeling/Modeling CHANGES,1.98,1.99 DatabaseChannel.py,1.11,1.12

[<sbi...@us...>]

Update of /cvsroot/modeling/ProjectModeling/Modeling
In directory sc8-pr-cvs1:/tmp/cvs-serv3082

Modified Files:
	CHANGES DatabaseChannel.py 
Log Message:
Fixed DatabaseChannel.fetchObject(): it was not MT-safe wrt Database
snapshots' caching when an EC in an other thread is garbage-collected in
the middle of fetchObject() (see comments in the code for further
details)


Index: CHANGES
===================================================================
RCS file: /cvsroot/modeling/ProjectModeling/Modeling/CHANGES,v
retrieving revision 1.98
retrieving revision 1.99
diff -C2 -d -r1.98 -r1.99
*** CHANGES	25 Apr 2003 18:13:33 -0000	1.98
--- CHANGES	6 May 2003 12:20:31 -0000	1.99
***************
*** 8,11 ****
--- 8,15 ----
    --------------------------------------------------------
  
+   * Fixed DatabaseChannel.fetchObject(): it was not MT-safe wrt Database
+     snapshots' caching in some circumstances (see comments in the code for
+     further details)
+ 
    * Added scripts/mdl_compile_model.py and update the __init__.py generated by
      mdl_generate_DB_schema.py so that it automatically tries to load the

Index: DatabaseChannel.py
===================================================================
RCS file: /cvsroot/modeling/ProjectModeling/Modeling/DatabaseChannel.py,v
retrieving revision 1.11
retrieving revision 1.12
diff -C2 -d -r1.11 -r1.12
*** DatabaseChannel.py	14 Mar 2003 11:40:06 -0000	1.11
--- DatabaseChannel.py	6 May 2003 12:20:32 -0000	1.12
***************
*** 150,229 ****
        self.databaseContext().registerLockedObjectWithGlobalID(globalID)
  
!     # Handle snapshot
!     # NB: ask delegate __TBD
!     if self.isRefreshingObjects() or self.isLocking():
!       # Unconditional refresh
!       database.recordSnapshotForGlobalID(snapshot, globalID)
!       if self.isRefreshingObjects():
!         # NB: isLocking-> no need to invalidate objects since two ECs cannot
!         # hold the same object at the same time
!         NC.postNotification(ObjectsChangedInStoreNotification, self,
!                             {UpdatedKey: (globalID,)})
!     else:
!       # Should the snapshot be updated? if there is already one, no update.
!       # __TBD  ask the DatabaseContext delegate whether we should refresh
!       # __TBD  and, if yes, post ObjectsChangedInStoreNotification
!       registeredSnapshot=database.snapshotForGlobalID(globalID)
!       if not registeredSnapshot:
          database.recordSnapshotForGlobalID(snapshot, globalID)
        else:
!        snapshot=registeredSnapshot
          
!     ec=self._editingContext
!     object=ec.objectForGlobalID(globalID)
! 
!     if object is not None and not object.isFault():
!       return object
! 
!     if object is not None and object.isFault():
!       #NC.removeObserver(object.faultHandler(), GlobalIDChangedNotification,
!       #                  globalID)
!       NC.removeObserver(ec, GlobalIDChangedNotification, globalID)
!       #object.clearFault()
        
!     #else:
!     cd=ClassDescription.classDescriptionForName(self._currentEntity.name())
!     # first, check that we do not have a fault registered under the ``root''
!     # GlobalID
!     root_cd_name=cd.rootClassDescription().entityName()
!     
!     if root_cd_name!=cd.entityName():
!       root_globalID=KeyGlobalID(root_cd_name, globalID.keyValues())
!       trace('Searching for possible fault w/ rootGlobalID=%s'%root_globalID)
!       possible_faulted_object=ec.objectForGlobalID(root_globalID)
!       if possible_faulted_object:
!         if possible_faulted_object.isFault():
!           trace('Found it: posting GlobalIDChangedNotification')
!           NC.postNotification(GlobalIDChangedNotification, root_globalID,
!                               {root_globalID: globalID})
!           object=possible_faulted_object
!           # useless: it did receive the notification, and it has unregistered
!           # itself from the list of the observers
!           #NC.removeObserver(object.faultHandler(),
!           #                  GlobalIDChangedNotification, globalID)
!           object.clearFault()
!           new_class=cd.classForInstances()
!           object.__class__=new_class
!           object.__class__.__init__(object)
!           
          else:
!           raise RuntimeError, "Serious: shouldn't happen, please report"
        else:
!         # create object
!         object=cd.createInstanceWithEditingContext(ec)
!         ec.recordObject(object, globalID)
!     else:
!       if not object:
!         # create object
!         object=cd.createInstanceWithEditingContext(ec)
!         ec.recordObject(object, globalID)
! 
!     # Initialize the new object or the cleared fault
!     try:
!       object.clearFault()
!     except:
!       pass
!     ec.initializeObject(object, globalID, ec)
! 
      return object
    
--- 150,256 ----
        self.databaseContext().registerLockedObjectWithGlobalID(globalID)
  
! 
!     # Now we need to lock the corresponding database object. Why?
!     #
!     # One could argue that e.g. since an EC forwards objectsWithFetchSpec()
!     # ultimately to its root object store --an ObjectStoreCoordinator--, and
!     # since OSC locks/unlocks itself before/after each operation, an other EC
!     # used in a concurrent thread can access the Database object (and its
!     # snapshots) in the meantime.
!     #
!     # This is true w.r.t. ECs standard operations, but there remains a case
!     # where a concurrent thread can change the Database's snapshots: when an
!     # EC is finalized and garbage-collected, it forgets its objects and
!     # decrements the corresponding snapshot reference count --at this time, if
!     # the ref.count falls down to zero, the snapshot is removed from the
!     # Database's snapshots cache.
!     #
!     # Now this can happen in another thread while in this thread, the snapshot
!     # has been retrieved but it has not been used yet by ec.initializeObject()
!     # (forwarded to and handled by DBContext.initializeObject()). When this
!     # happens, Database.incrementSnapshotCountForGlobalID() called by
!     # DBContext.initializeObject() raises KeyError on the corresp. GlobalID
!     # since the corresponding snapshot has been thrown away.
!     #
!     database.lock()
!     try:
!       # Handle snapshot
!       # NB: ask delegate __TBD
!       if self.isRefreshingObjects() or self.isLocking():
!         # Unconditional refresh
          database.recordSnapshotForGlobalID(snapshot, globalID)
+         if self.isRefreshingObjects():
+           # NB: isLocking-> no need to invalidate objects since two ECs cannot
+           # hold the same object at the same time
+           NC.postNotification(ObjectsChangedInStoreNotification, self,
+                               {UpdatedKey: (globalID,)})
        else:
!         # Should the snapshot be updated? if there is already one, no update.
!         # __TBD  ask the DatabaseContext delegate whether we should refresh
!         # __TBD  and, if yes, post ObjectsChangedInStoreNotification
!         registeredSnapshot=database.snapshotForGlobalID(globalID)
!         if not registeredSnapshot:
!           database.recordSnapshotForGlobalID(snapshot, globalID)
!         else:
!           snapshot=registeredSnapshot
!           
!       ec=self._editingContext
!       object=ec.objectForGlobalID(globalID)
!       
!       if object is not None and not object.isFault():
!         return object
!       
!       if object is not None and object.isFault():
!         #NC.removeObserver(object.faultHandler(), GlobalIDChangedNotification,
!         #                  globalID)
!         NC.removeObserver(ec, GlobalIDChangedNotification, globalID)
!         #object.clearFault()
          
!       #else:
!       cd=ClassDescription.classDescriptionForName(self._currentEntity.name())
!       # first, check that we do not have a fault registered under the ``root''
!       # GlobalID
!       root_cd_name=cd.rootClassDescription().entityName()
        
!       if root_cd_name!=cd.entityName():
!         root_globalID=KeyGlobalID(root_cd_name, globalID.keyValues())
!         trace('Searching for possible fault w/ rootGlobalID=%s'%root_globalID)
!         possible_faulted_object=ec.objectForGlobalID(root_globalID)
!         if possible_faulted_object:
!           if possible_faulted_object.isFault():
!             trace('Found it: posting GlobalIDChangedNotification')
!             NC.postNotification(GlobalIDChangedNotification, root_globalID,
!                                 {root_globalID: globalID})
!             object=possible_faulted_object
!             # useless: it did receive the notification, and it has unregistered
!             # itself from the list of the observers
!             #NC.removeObserver(object.faultHandler(),
!             #                  GlobalIDChangedNotification, globalID)
!             object.clearFault()
!             new_class=cd.classForInstances()
!             object.__class__=new_class
!             object.__class__.__init__(object)
!             
!           else:
!             raise RuntimeError, "Serious: shouldn't happen, please report"
          else:
!           # create object
!           object=cd.createInstanceWithEditingContext(ec)
!           ec.recordObject(object, globalID)
        else:
!         if not object:
!           # create object
!           object=cd.createInstanceWithEditingContext(ec)
!           ec.recordObject(object, globalID)
!       
!       # Initialize the new object or the cleared fault
!       try:
!         object.clearFault()
!       except:
!         pass
!       ec.initializeObject(object, globalID, ec)
!     finally:
!       database.unlock()
!       
      return object
    
***************
*** 332,336 ****
      if not self._adaptorChannel.isOpen():
        self._adaptorChannel.openChannel()
! 
      #self._adaptorChannel.executeExpression(sqlExpr)
      self._adaptorChannel.selectAttributes(entity.attributesToFetch(),
--- 359,363 ----
      if not self._adaptorChannel.isOpen():
        self._adaptorChannel.openChannel()
!     
      #self._adaptorChannel.executeExpression(sqlExpr)
      self._adaptorChannel.selectAttributes(entity.attributesToFetch(),
***************
*** 338,342 ****
                                            self._isLocking,
                                            entity)
-       
        
    def setCurrentEditingContext(self, anEditingContext):
--- 365,368 ----