Allow serial to be returned as late as tpc_finish

This makes possible for storage to allocate serial inside tpc_finish,
removing the requirement to serialise 2PC's second phase phase (tpc_vote
to tpc_finish/tpc_abort).
Co-Authored-By: Julien Muchembled <jm@nexedi.com>

src/ZODB/Connection.py

@@ -808,7 +808,16 @@ class Connection(ExportImport, object):
 #       to be able to read any updated data until we've had a chance
 #       to send an invalidation message to all of the other
 #       connections!
-        self._storage.tpc_finish(transaction, callback)
+        serial = self._storage.tpc_finish(transaction, callback)
+        if serial is not None:
+            assert type(serial) is bytes, repr(serial)
+            for oid_iterator in self._modified, self._creating:
+                for oid in oid_iterator:
+                    obj = self._cache.get(oid)
+                    # Ignore missing objects and don't update ghosts.
+                    if obj is not None and obj._p_changed is not None:
+                        obj._p_changed = 0
+                        obj._p_serial = serial
         self._tpc_cleanup()
 
     def sortKey(self):

src/ZODB/interfaces.py

@@ -776,6 +776,10 @@ class IStorage(Interface):
         called while the storage transaction lock is held.  It takes
         the new transaction id generated by the transaction.
 
+        The return value can be either None or a serial giving new
+        serial for objects whose ids were passed to previous store calls
+        in the same transaction, and for which no serial was returned
+        from either store or tpc_vote for objects passed to store.
         """
 
     def tpc_vote(transaction):
@@ -794,14 +798,14 @@ class IStorage(Interface):
         The return value can be either None or a sequence of object-id
         and serial pairs giving new serials for objects who's ids were
         passed to previous store calls in the same transaction.
-        After the tpc_vote call, new serials must have been returned,
-        either from tpc_vote or store for objects passed to store.
 
         A serial returned in a sequence of oid/serial pairs, may be
         the special value ZODB.ConflictResolution.ResolvedSerial to
         indicate that a conflict occured and that the object should be
         invalidated.
 
+        After the tpc_vote call, all solved conflicts must have been notified,
+        either from tpc_vote or store for objects passed to store.
         """
 
 

src/ZODB/tests/BasicStorage.py

@@ -69,8 +69,10 @@ class BasicStorage:
         r1 = self._storage.store(oid, None, zodb_pickle(MinPO(11)),
                                        '', txn)
         r2 = self._storage.tpc_vote(txn)
-        self._storage.tpc_finish(txn)
+        serial = self._storage.tpc_finish(txn)
         newrevid = handle_serials(oid, r1, r2)
+        if newrevid is None and serial is not None:
+            newrevid = serial
         data, revid = self._storage.load(oid, '')
         value = zodb_unpickle(data)
         eq(value, MinPO(11))

src/ZODB/tests/MTStorage.py

@@ -152,10 +152,12 @@ class StorageClientThread(TestThread):
         r2 = self.storage.tpc_vote(t)
         self.pause()
 
-        self.storage.tpc_finish(t)
+        serial = self.storage.tpc_finish(t)
         self.pause()
 
         revid = handle_serials(oid, r1, r2)
+        if serial is not None and revid is None:
+            revid = serial
         self.oids[oid] = revid
 
 class ExtStorageClientThread(StorageClientThread):

src/ZODB/tests/RevisionStorage.py

@@ -150,10 +150,12 @@ class RevisionStorage:
                 # Finish the transaction
                 r2 = self._storage.tpc_vote(t)
                 newrevid = handle_serials(oid, r1, r2)
-                self._storage.tpc_finish(t)
+                serial = self._storage.tpc_finish(t)
             except:
                 self._storage.tpc_abort(t)
                 raise
+            if serial is not None and newrevid is None:
+                newrevid = serial
             return newrevid
         revid1 = helper(1, None, 1)
         revid2 = helper(2, revid1, 2)

src/ZODB/tests/StorageTestBase.py

@@ -132,7 +132,7 @@ def handle_serials(oid, *args):
 
     A helper for function _handle_all_serials().
     """
-    return handle_all_serials(oid, *args)[oid]
+    return handle_all_serials(oid, *args).get(oid)
 
 def import_helper(name):
     __import__(name)
@@ -189,7 +189,9 @@ class StorageTestBase(ZODB.tests.util.TestCase):
             # Finish the transaction
             r2 = self._storage.tpc_vote(t)
             revid = handle_serials(oid, r1, r2)
-            self._storage.tpc_finish(t)
+            serial = self._storage.tpc_finish(t)
+            if serial is not None and revid is None:
+                revid = serial
         except:
             self._storage.tpc_abort(t)
             raise
@@ -209,8 +211,8 @@ class StorageTestBase(ZODB.tests.util.TestCase):
         self._storage.tpc_begin(t)
         undo_result = self._storage.undo(tid, t)
         vote_result = self._storage.tpc_vote(t)
-        self._storage.tpc_finish(t)
-        if expected_oids is not None:
+        serial = self._storage.tpc_finish(t)
+        if expected_oids is not None and serial is None:
             oids = list(undo_result[1]) if undo_result else []
             oids.extend(oid for (oid, _) in vote_result or ())
             self.assertEqual(len(oids), len(expected_oids), repr(oids))

src/ZODB/tests/TransactionalUndoStorage.py

@@ -73,6 +73,12 @@ class TransactionalUndoStorage:
     def _transaction_newserial(self, oid):
         return self.__serials[oid]
 
+    def _transaction_finish(self, t, oid_list):
+        tid = self._storage.tpc_finish(t)
+        if tid is not None:
+            for oid in oid_list:
+                self.__serials[oid] = tid
+
     def _multi_obj_transaction(self, objs):
         newrevs = {}
         t = Transaction()
@@ -82,7 +88,7 @@ class TransactionalUndoStorage:
             self._transaction_store(oid, rev, data, '', t)
             newrevs[oid] = None
         self._transaction_vote(t)
-        self._storage.tpc_finish(t)
+        self._transaction_finish(t, [x[0] for x in objs])
         for oid in newrevs.keys():
             newrevs[oid] = self._transaction_newserial(oid)
         return newrevs
@@ -219,9 +225,9 @@ class TransactionalUndoStorage:
         self._transaction_store(oid2, revid2, p51, '', t)
         # Finish the transaction
         self._transaction_vote(t)
+        self._transaction_finish(t, [oid1, oid2])
         revid1 = self._transaction_newserial(oid1)
         revid2 = self._transaction_newserial(oid2)
-        self._storage.tpc_finish(t)
         eq(revid1, revid2)
         # Update those same two objects
         t = Transaction()
@@ -231,9 +237,9 @@ class TransactionalUndoStorage:
         self._transaction_store(oid2, revid2, p52, '', t)
         # Finish the transaction
         self._transaction_vote(t)
+        self._transaction_finish(t, [oid1, oid2])
         revid1 = self._transaction_newserial(oid1)
         revid2 = self._transaction_newserial(oid2)
-        self._storage.tpc_finish(t)
         eq(revid1, revid2)
         # Make sure the objects have the current value
         data, revid1 = self._storage.load(oid1, '')
@@ -289,10 +295,11 @@ class TransactionalUndoStorage:
         tid1 = info[1]['id']
         t = Transaction()
         oids = self._begin_undos_vote(t, tid, tid1)
-        self._storage.tpc_finish(t)
+        serial = self._storage.tpc_finish(t)
         # We may get the finalization stuff called an extra time,
         # depending on the implementation.
-        self.assertEqual(set(oids), set((oid1, oid2)))
+        if serial is None:
+            self.assertEqual(set(oids), {oid1, oid2})
         data, revid1 = self._storage.load(oid1, '')
         eq(zodb_unpickle(data), MinPO(30))
         data, revid2 = self._storage.load(oid2, '')
@@ -326,7 +333,7 @@ class TransactionalUndoStorage:
         self._transaction_store(oid2, revid2, p52, '', t)
         # Finish the transaction
         self._transaction_vote(t)
-        self._storage.tpc_finish(t)
+        self._transaction_finish(t, [oid1, oid2])
         revid1 = self._transaction_newserial(oid1)
         revid2 = self._transaction_newserial(oid2)
         eq(revid1, revid2)
@@ -346,7 +353,7 @@ class TransactionalUndoStorage:
         self._transaction_store(oid2, revid2, p53, '', t)
         # Finish the transaction
         self._transaction_vote(t)
-        self._storage.tpc_finish(t)
+        self._transaction_finish(t, [oid1, oid2])
         revid1 = self._transaction_newserial(oid1)
         revid2 = self._transaction_newserial(oid2)
         eq(revid1, revid2)
@@ -358,7 +365,8 @@ class TransactionalUndoStorage:
         tid = info[1]['id']
         t = Transaction()
         oids = self._begin_undos_vote(t, tid)
-        self._storage.tpc_finish(t)
+        serial = self._storage.tpc_finish(t)
+        if serial is None:
             eq(len(oids), 1)
             self.assertTrue(oid1 in oids)
             self.assertTrue(not oid2 in oids)
@@ -398,7 +406,7 @@ class TransactionalUndoStorage:
         self._transaction_store(oid1, revid1, p81, '', t)
         self._transaction_store(oid2, revid2, p91, '', t)
         self._transaction_vote(t)
-        self._storage.tpc_finish(t)
+        self._transaction_finish(t, [oid1, oid2])
         revid1 = self._transaction_newserial(oid1)
         revid2 = self._transaction_newserial(oid2)
         eq(revid1, revid2)

src/ZODB/tests/testDemoStorage.py

@@ -42,6 +42,8 @@ from zope.testing import renormalizing
 # With the following monkey-patch, we can test the different ways
 # to update _p_changed/_p_serial status of committed oids.
 
+from ZODB.ConflictResolution import ResolvedSerial
+
 class DemoStorage(ZODB.DemoStorage.DemoStorage):
 
     delayed_store = False
@@ -52,6 +54,9 @@ class DemoStorage(ZODB.DemoStorage.DemoStorage):
 
     def store(self, oid, *args):
         s = super(DemoStorage, self).store(oid, *args)
+        if s != ResolvedSerial:
+            assert type(s) is bytes, s
+            return
         if not self.delayed_store:
             return s
         self.__stored.append((oid, s))
@@ -63,6 +68,15 @@ class DemoStorage(ZODB.DemoStorage.DemoStorage):
         assert s is None, s
         return self.__stored if self.delayed_store else s
 
+    def tpc_finish(self, transaction, func = lambda tid: None):
+        r = []
+        def callback(tid):
+            func(tid)
+            r.append(tid)
+        tid = super(DemoStorage, self).tpc_finish(transaction, callback)
+        assert tid is None, tid
+        return r[0]
+
 ZODB.DemoStorage.DemoStorage = DemoStorage
 
 class DemoStorageTests(