New TransientObjectContainer implementation.

Changes:

 - More stable under high usage, especially in the face of
   situations under which there are many ZODB conflict
   errors. The previous implementation had stability problems
   when many conflict errors were encountered; especially
   conflicts that were generated as a result of a simultaneous
   change to a subobject of the TOC (such as in the case of a Zope
   application which makes heavy use of both frames and
   sessions).

 - More conflict-resistant.  Instead of ignoring the likelihood
   that multiple threads will attempt to perform the same actions
   simultaneously in methods of the TOC (which often causes
   conflicts), the new implementation attempts to avoid conflicts
   by employing a chance-based housekeeping model.  In this model,
   one thread is "elected" by chance to do the kinds of tasks that
   cause the most conflicts.

 - Now uses a "timeslice" based model instead of a "ring" based
   model.  This also helps cut down on conflicts and makes
   the code slighly less obfuscated (not much, though! ;-)

 - Quite a few more comments in the code.

 - Changes to the sessioning stresstest (which exposed the
   bug that made me reimplement the TOC in the first place).

 - Updates to unit tests.

 - A "HowTransienceWorks.stx" document which attempts to
   explain how the code works.  It's not stellar, but
   it's a start.

 - Changes to the TransientObject class that the TOC
   hands out (typically as a "session data object"), in order
   to make invalidation less Rube-Goldberg-ish.

The structure of the TOC object has changed enough that in order to
maintain b/w compatibility, an in-place upgrade of "old" instances
is implied by running them with this code.   "Upgraded" instances
are not backwards-incompatible, however, so folks can hopefully
move back and forth between Zope versions without much hassle.

lib/python/Products/Sessions/stresstests/stresstestMultiThread.py

@@ -24,7 +24,9 @@ from Products.Sessions.SessionDataManager import \
 from Products.Transience.Transience import \
     TransientObjectContainer, TransientObject
 from Products.TemporaryFolder.TemporaryFolder import MountedTemporaryFolder
-from ZODB.POSException import InvalidObjectReference, ConflictError
+from Products.TemporaryFolder.LowConflictConnection import LowConflictConnection
+from ZODB.Connection import Connection
+from ZODB.POSException import InvalidObjectReference, ConflictError, ReadConflictError, BTreesConflictError
 from DateTime import DateTime
 from unittest import TestCase, TestSuite, TextTestRunner, makeSuite
 import time, threading, random
@@ -32,6 +34,7 @@ from cPickle import UnpickleableError
 from ZODB.DemoStorage import DemoStorage
 from OFS.Application import Application
 import sys
+from zLOG import log_time
 sys.setcheckinterval(200)
 
 tf_name = 'temp_folder'
@@ -65,7 +68,7 @@ def _populate(app):
     bidmgr = BrowserIdManager(idmgr_name)
     tf = MountedTemporaryFolder(tf_name, title="Temporary Folder")
     toc = TransientObjectContainer(toc_name, title='Temporary '
-        'Transient Object Container', timeout_mins=20)
+        'Transient Object Container', timeout_mins=1)
     session_data_manager=SessionDataManager(id='session_data_manager',
         path='/'+tf_name+'/'+toc_name, title='Session Data Manager')
 
@@ -89,7 +92,7 @@ def _populate(app):
     get_transaction().commit()
 
 class TestMultiThread(TestCase):
-    def testNonOverlappingBrowserIds(self):
+    def testOverlappingBrowserIds(self):
         readers = []
         writers = []
         readiters = 20
@@ -115,10 +118,7 @@ class TestMultiThread(TestCase):
         while threading.activeCount() > 1:
             time.sleep(1)
         
-        for thread in readers:
-            assert thread.out == [], thread.out
-
-    def testOverlappingBrowserIds(self):
+    def testNonOverlappingBrowserIds(self):
         readers = []
         writers = []
         readiters = 20
@@ -144,9 +144,6 @@ class TestMultiThread(TestCase):
         while threading.activeCount() > 1:
             time.sleep(1)
         
-        for thread in readers:
-            assert thread.out == [], thread.out
-
 class BaseReaderWriter(threading.Thread):
     def __init__(self, db, iters, sdm_name):
         self.conn = db.open()
@@ -166,13 +163,23 @@ class BaseReaderWriter(threading.Thread):
                 try:
                     self.run1()
                     return
+                except ReadConflictError:
+                    print "read conflict"
+                except BTreesConflictError:
+                    print "btrees conflict"
                 except ConflictError:
-                    i = i + 1
-                    #print "conflict %d" % i
-                    if i > 3: raise
+                    print "general conflict"
+                except:
+                    get_transaction().abort()
+                    print log_time()
+                    raise
+                i = i + 1
+                get_transaction().abort()
+                time.sleep(random.randrange(5) * .1)
         finally:
             self.conn.close()
             del self.app
+            print i
             
 class ReaderThread(BaseReaderWriter):
     def run1(self):

lib/python/Products/Transience/HowTransienceWorks.stx

+How Transience Works
+
+  The object responsible for managing the expiration of "transient"
+  objects is the TransientObjectContainer, the class definition for
+  which is located in
+  Products.Transience.Transience.TransientObjectContainer.  An
+  instance of this class is found in the default Zope installation at
+  /temp_folder/session_data.
+
+  The TransientObjectContainer (TOC) holds Transient Objects (TOs).
+
+  A TO is obtained via its container via a call to
+  TOC.new_or_existing(key), where "key" is usually the "browser id"
+  associated with a visitor (See Products.Session.BrowserIdManager).
+
+  If the TOC has a "current" TO corresponding to "key", it is
+  returned.
+
+  If the TOC does not have a "current" TO corresponding to "key", (due
+  to the expiration of the TO or because it never existed in the first
+  place) a "new" TO is manufactured and returned.
+
+Timeslices
+
+  Transience defines the notion of a "timeslice".  A "timeslice" is an
+  integer that represents some "slice" of time, defined by a "period".
+  For example, if a period is 20 seconds long, three ordered time
+  slices might be expressed as 0, 20, and 40.  The next timeslice
+  would be 60, and so on.  For an absolute time to "belong" to a
+  timeslice, it would need to be equal to or greater than one
+  timeslice integer, but less than the subsequent timeslice integer.
+
+Data Structures Maintained by a Transient Object Container
+
+  The TOC maintains five important kinds of data structures:
+
+  - a "_data" structure, which is an IOBTree mapping a "timeslice"
+    integer to a "bucket" (see next bullet for definition of bucket).
+
+  - One or more "buckets", which are OOBTree objects which map a "key"
+    (usually browser id) to a TransientObject.  Buckets are stored
+    inside of the "_data" structure.  There is a concept of a
+    "current" bucket, which is the bucket that is contained within the
+    _data structured with a key equal to the "current" timeslice.
+
+  - An "index" which is an OOBTree mapping transient object "key" to
+    "timeslice", letting us quickly figure out which element in the _data
+    mapping contains the transient object related to the key.  It is
+    stored as the attribute "_index" of the TOC.  When calling code
+    wants to obtain a Transient Object, its key is looked up in the
+    index, which returns a timeslice.  We ask the _data structure for the
+    bucket it has stored under that timeslice.  Then the bucket is asked
+    for the object stored under the key.  This returns the Transient Object.
+
+  - A "last timeslice" integer, which is equal to the "last" timeslice
+    under which TOC housekeeping operations were performed.
+
+  - A "next to deindex" integer, which is a timeslice
+    representing the next bucket which requires "deindexing"
+    (the removal of all the keys of the bucket from the index).
+
+  When a Transient Object is created via new_or_existing, it is added
+  to the "current" bucket.  As time goes by, the bucket to which the
+  TO was added ceases to be the "current" bucket.  If the transient
+  object is "accessed" (it is called up out of the TOC via the TOC's
+  'get' method), it is again moved to the "current" bucket defined by
+  the current time's timeslice.
+
+  During the course of normal operations, a TransientObject will move
+  from an "old" bucket to the "current" bucket many times, as long as
+  it continues to be accessed.  It is possible for a TransientObject
+  to *never* expire, as long as it is called up out of its TOC often
+  enough.
+
+  If a TransientObject is not accessed in the period of time defined by
+  the TOC's "timeout", it is deindexed and eventually garbage collected.
+
+How the TransientObjectContainer Determines if a TransientObject is "Current"
+
+  A TO is current if it has an entry in the "index".  When a TO has an
+  entry in the index, it implies that the TO resides in a bucket that
+  is no "older" than the TOC timeout period, based on the bucket's
+  timeslice.
+
+Housekeeping: Finalization, Notification, Garbage Collection, and
+Bucket Replentishing
+
+  The TOC performs "deindexing", "notification", "garbage
+  collection", and "bucket replentishing".  It performs these tasks
+  "in-band".  This means that the TOC does not maintain a separate
+  thread that wakes up every so often to do these housekeeping tasks.
+  Instead, during the course of normal operations, the TOC
+  opportunistically performs them.
+
+  Deindexing is defined as the act of making an "expired" TO
+  inaccessible (by deleting it from the "index").  After a TO is
+  deindexed, it may not be used by application code any longer,
+  although it may "stick around" in a bucket for a while until the
+  bucket is eventually garbage collected.
+
+  Notification is defined as optionally calling a function at TOC
+  finalization time.  The optional function call is user-defined, but
+  it is managed by the "notifyDestruct" method of the TOC.
+
+  Garbage collection is defined as deleting "expired" buckets in the
+  _data structure (the _data structure maps a timeslice to a bucket).
+
+  Bucket replentishing is defined as the action of (opportunistically)
+  creating more buckets to insert into the the _data structure,
+  replacing ones that are deleted during garbage collection.  The act
+  of deleting a bucket does not necessarily imply that a new bucket
+  will be immediately created thereafter.  We create new buckets in
+  batches to reduce the possibility of conflicts.
+
+Goals
+
+ - A low number of ZODB conflict errors (which reduce performance).
+
+ - Stability.
+
+To Do
+
+  - Testing under ZEO.
+

lib/python/Products/Transience/TransienceInterfaces.py

@@ -149,8 +149,8 @@ class DictionaryLike(Interface.Base):
 
     def get(k, default='marker'):
         """
-        Return value associated with key k.  If k does not exist and default
-        is not marker, return default, else raise KeyError.
+        Return value associated with key k.  Return None or default if k
+        does not exist.
         """
 
     def has_key(k):

lib/python/Products/Transience/TransientObject.py

@@ -13,10 +13,10 @@
 """
 Simple ZODB-based transient object implementation.
 
-$Id: TransientObject.py,v 1.6 2002/06/11 15:19:38 chrism Exp $
+$Id: TransientObject.py,v 1.7 2002/06/21 01:51:43 chrism Exp $
 """
 
-__version__='$Revision: 1.6 $'[11:-2]
+__version__='$Revision: 1.7 $'[11:-2]
 
 from Persistence import Persistent
 from Acquisition import Implicit
@@ -74,6 +74,13 @@ class TransientObject(Persistent, Implicit):
     #
 
     def invalidate(self):
+        if hasattr(self, '_invalid'):
+            # we dont want to invalidate twice
+            return
+        trans_ob_container = getattr(self, 'aq_parent', None)
+        if trans_ob_container is not None:
+            if trans_ob_container.has_key(self.token):
+                del trans_ob_container[self.token]
         self._invalid = None
 
     def isValid(self):

lib/python/Products/Transience/tests/testTimeoutRelated.py

 import sys, os, time, unittest
 
+if __name__=='__main__':
+    sys.path.insert(0, '..')
+    sys.path.insert(0, '../../..')
+
 import ZODB # in order to get Persistence.Persistent working
 from Testing import makerequest
 import Acquisition
@@ -74,7 +78,7 @@ class TestLastAccessed(TestBase):
         sdo = self.app.sm.new_or_existing('TempObject')
         la1 = sdo.getLastAccessed()
         fauxtime.sleep(WRITEGRANULARITY + 1)
-        sdo = self.app.sm['TempObject']
+        sdo = self.app.sm.get('TempObject')
         assert sdo.getLastAccessed() > la1, (sdo.getLastAccessed(), la1)
 
 class TestNotifications(TestBase):
@@ -90,13 +94,15 @@ class TestNotifications(TestBase):
         self.app.sm.setDelNotificationTarget(delNotificationTarget)
         sdo = self.app.sm.new_or_existing('TempObject')
         timeout = self.timeout * 60
-        fauxtime.sleep(timeout + (timeout * .33))
-        try: sdo1 = self.app.sm['TempObject']
-        except KeyError: pass
+        fauxtime.sleep(timeout + (timeout * .75))
+        sdo1 = self.app.sm.get('TempObject')
+        for x in range(1, 100):
+            # force the sdm to do housekeeping
+            self.app.sm._getCurrentBucket()
         now = fauxtime.time()
         k = sdo.get('endtime')
-        assert type(k) == type(now)
-        assert k <= now
+        assert (type(k) == type(now)), type(k)
+        assert k <= now, (k, now)
 
 def addNotificationTarget(item, context):
     item['starttime'] = fauxtime.time()

lib/python/Products/Transience/tests/testTransientObjectContainer.py

@@ -12,6 +12,9 @@
 ##############################################################################
 import sys, os, time, random, unittest
 
+if __name__ == "__main__":
+    sys.path.insert(0, '../../..')
+
 import ZODB
 from Products.Transience.Transience import TransientObjectContainer,\
      MaxTransientObjectsExceeded
@@ -23,7 +26,7 @@ from unittest import TestCase, TestSuite, TextTestRunner, makeSuite
 import time as oldtime
 import fauxtime
 
-class TestTransientObjectContainer(TestCase):
+class TestBase(TestCase):
     def setUp(self):
         Products.Transience.Transience.time = fauxtime
         Products.Transience.TransientObject.time = fauxtime
@@ -36,6 +39,7 @@ class TestTransientObjectContainer(TestCase):
         Products.Transience.Transience.time = oldtime
         Products.Transience.TransientObject.time = oldtime
 
+class TestTransientObjectContainer(TestBase):
     def testGetItemFails(self):
         self.assertRaises(KeyError, self._getitemfail)
 
@@ -280,6 +284,36 @@ class TestTransientObjectContainer(TestCase):
             except KeyError:
                 if self.t.has_key(x): assert 1==2,"failed to delete %s" % x
 
+    def testChangingTimeoutWorks(self):
+        # 1 minute
+        for x in range(10, 110):
+            self.t[x] = x
+        fauxtime.sleep(self.timeout * (self.errmargin+1))
+        assert len(self.t.keys()) == 0, len(self.t.keys())
+
+        # 2 minutes
+        self.t._setTimeout(self.timeout/60*2)
+        self.t._reset()
+        for x in range(10, 110):
+            self.t[x] = x
+        fauxtime.sleep(self.timeout)
+        assert len(self.t.keys()) == 100, len(self.t.keys())
+        fauxtime.sleep(self.timeout * (self.errmargin+1))
+        assert len(self.t.keys()) == 0, len(self.t.keys())
+
+        # 3 minutes
+        self.t._setTimeout(self.timeout/60*3)
+        self.t._reset()
+        for x in range(10, 110):
+            self.t[x] = x
+        fauxtime.sleep(self.timeout)
+        assert len(self.t.keys()) == 100, len(self.t.keys())
+        fauxtime.sleep(self.timeout)
+        assert len(self.t.keys()) == 100, len(self.t.keys())
+        fauxtime.sleep(self.timeout * (self.errmargin+1))
+        assert len(self.t.keys()) == 0, len(self.t.keys())
+
+
     def testItemsGetExpired(self):
         for x in range(10, 110):
             self.t[x] = x
@@ -326,14 +360,14 @@ class TestTransientObjectContainer(TestCase):
         fauxtime.sleep(self.timeout * (self.errmargin+1))
         assert len(self.t.keys()) == 0, len(self.t.keys())
 
-    def testGetItemDelaysTimeout(self):
+    def testGetDelaysTimeout(self):
         for x in range(10, 110):
             self.t[x] = x
         # current bucket will become old after we sleep for a while.
         fauxtime.sleep(self.timeout/2)
         # these items will be added to the new current bucket by getitem
         for x in range(10, 110):
-            self.t[x]
+            self.t.get(x)
         fauxtime.sleep(self.timeout/2)
         assert len(self.t.keys()) == 100, len(self.t.keys())
         for x in range(10, 110):
@@ -344,7 +378,7 @@ class TestTransientObjectContainer(TestCase):
             self.t[x] = x
         # current bucket will become old after we sleep for a while.
         fauxtime.sleep(self.timeout/2)
-        # these items will be added to the new current bucket by getitem
+        # these items will be added to the new current bucket by setitem
         for x in range(10, 110):
             self.t[x] = x + 1
         fauxtime.sleep(self.timeout/2)
@@ -352,19 +386,6 @@ class TestTransientObjectContainer(TestCase):
         for x in range(10, 110):
             assert self.t[x] == x + 1
 
-    def testGetDelaysTimeout(self):
-        for x in range(10, 110):
-            self.t[x] = x
-        # current bucket will become old after we sleep for a while.
-        fauxtime.sleep(self.timeout/2)
-        # these items will be added to the new current bucket by getitem
-        for x in range(10, 110):
-            self.t.get(x)
-        fauxtime.sleep(self.timeout/2)
-        assert len(self.t.keys()) == 100, len(self.t.keys())
-        for x in range(10, 110):
-            assert self.t[x] == x
-
     def testLen(self):
         added = {}
         r = range(10, 1010)
@@ -428,6 +449,7 @@ def lsubtract(l1, l2):
 
 def test_suite():
     testsuite = makeSuite(TestTransientObjectContainer, 'test')
+    #testsuite = makeSuite(TestBase, 'test')
     alltests = TestSuite((testsuite,))
     return alltests