Merge pull request #38 from zopefoundation/client-side-conflict-resol…

…ution

Client side conflict resolution

src/ZEO/ClientStorage.py

@@ -34,6 +34,7 @@
 import zc.lockfile
 import ZODB
 import ZODB.BaseStorage
+import ZODB.ConflictResolution
 import ZODB.interfaces
 import zope.interface
 import six
@@ -75,7 +76,7 @@ def get_timestamp(prev_ts=None):
 MB = 1024**2
 
 @zope.interface.implementer(ZODB.interfaces.IMultiCommitStorage)
-class ClientStorage(object):
+class ClientStorage(ZODB.ConflictResolution.ConflictResolvingStorage):
     """A storage class that is a network client to a remote storage.
 
     This is a faithful implementation of the Storage API.
@@ -331,6 +332,7 @@ def registerDB(self, db):
 
         The storage isn't really ready to use until after this call.
         """
+        super(ClientStorage, self).registerDB(db)
         self._db = db
 
     def is_connected(self, test=False):
@@ -722,13 +724,33 @@ def tpc_vote(self, txn):
         """
         tbuf = self._check_trans(txn, 'tpc_vote')
         try:
-            for oid in self._call('vote', id(txn)) or ():
-                tbuf.serial(oid, ResolvedSerial)
+
+            conflicts = True
+            vote_attempts = 0
+            while conflicts and vote_attempts < 9: # 9? Mainly avoid inf. loop
+                conflicts = False
+                for oid in self._call('vote', id(txn)) or ():
+                    if isinstance(oid, dict):
+                        # Conflict, let's try to resolve it
+                        conflicts = True
+                        conflict = oid
+                        oid = conflict['oid']
+                        committed, read = conflict['serials']
+                        data = self.tryToResolveConflict(
+                            oid, committed, read, conflict['data'])
+                        self._async('storea', oid, committed, data, id(txn))
+                        tbuf.resolve(oid, data)
+                    else:
+                        tbuf.serial(oid, ResolvedSerial)
+
+                vote_attempts += 1
+
         except POSException.StorageTransactionError:
             # Hm, we got disconnected and reconnected bwtween
             # _check_trans and voting. Let's chack the transaction again:
             self._check_trans(txn, 'tpc_vote')
             raise
+
         except POSException.ConflictError as err:
             oid = getattr(err, 'oid', None)
             if oid is not None:
@@ -745,8 +767,8 @@ def tpc_vote(self, txn):
         if tbuf.exception:
             raise tbuf.exception
 
-        if tbuf.resolved:
-            return list(tbuf.resolved)
+        if tbuf.server_resolved or tbuf.client_resolved:
+            return list(tbuf.server_resolved) + list(tbuf.client_resolved)
         else:
             return None
 

src/ZEO/StorageServer.py

@@ -89,6 +89,7 @@ class ZEOStorage:
 
     def __init__(self, server, read_only=0):
         self.server = server
+        self.client_conflict_resolution = server.client_conflict_resolution
         # timeout and stats will be initialized in register()
         self.read_only = read_only
         # The authentication protocol may define extra methods.
@@ -334,6 +335,7 @@ def tpc_begin(self, id, user, description, ext, tid=None, status=" "):
         t._extension = ext
 
         self.serials = []
+        self.conflicts = {}
         self.invalidated = []
         self.txnlog = CommitLog()
         self.blob_log = []
@@ -413,6 +415,7 @@ def _try_to_vote(self, delay=None):
 
         self.locked, delay = self.server.lock_storage(self, delay)
         if self.locked:
+            result = None
             try:
                 self.log(
                     "Preparing to commit transaction: %d objects, %d bytes"
@@ -433,13 +436,29 @@ def _try_to_vote(self, delay=None):
                     oid, oldserial, data, blobfilename = self.blob_log.pop()
                     self._store(oid, oldserial, data, blobfilename)
 
-                serials = self.storage.tpc_vote(self.transaction)
-                if serials:
-                    if not isinstance(serials[0], bytes):
-                        serials = (oid for (oid, serial) in serials
-                                   if serial == ResolvedSerial)
 
-                    self.serials.extend(serials)
+                if not self.conflicts:
+                    try:
+                        serials = self.storage.tpc_vote(self.transaction)
+                    except ConflictError as err:
+                        if (self.client_conflict_resolution and
+                            err.oid and err.serials and err.data
+                            ):
+                            self.conflicts[err.oid] = dict(
+                                oid=err.oid, serials=err.serials, data=err.data)
+                        else:
+                            raise
+                    else:
+                        if serials:
+                            self.serials.extend(serials)
+                        result = self.serials
+
+                if self.conflicts:
+                    result = list(self.conflicts.values())
+                    self.storage.tpc_abort(self.transaction)
+                    self.server.unlock_storage(self)
+                    self.locked = False
+                    self.server.stop_waiting(self)
 
             except Exception as err:
                 self.storage.tpc_abort(self.transaction)
@@ -457,9 +476,9 @@ def _try_to_vote(self, delay=None):
                     raise
             else:
                 if delay is not None:
-                    delay.reply(self.serials)
+                    delay.reply(result)
                 else:
-                    return self.serials
+                    return result
 
         else:
             return delay
@@ -559,28 +578,24 @@ def _checkread(self, oid, serial):
             oid, serial, self.transaction)
 
     def _store(self, oid, serial, data, blobfile=None):
-        if blobfile is None:
-            newserial = self.storage.store(
-                oid, serial, data, '', self.transaction)
+        try:
+            if blobfile is None:
+                self.storage.store(oid, serial, data, '', self.transaction)
+            else:
+                self.storage.storeBlob(
+                    oid, serial, data, blobfile, '', self.transaction)
+        except ConflictError as err:
+            if self.client_conflict_resolution and err.serials:
+                self.conflicts[oid] = dict(
+                    oid=oid, serials=err.serials, data=data)
+            else:
+                raise
         else:
-            newserial = self.storage.storeBlob(
-                oid, serial, data, blobfile, '', self.transaction)
-
-        if serial != b"\0\0\0\0\0\0\0\0":
-            self.invalidated.append(oid)
-
-        if newserial:
+            if oid in self.conflicts:
+                del self.conflicts[oid]
 
-            if isinstance(newserial, bytes):
-                newserial = [(oid, newserial)]
-
-            for oid, s in newserial:
-
-                if s == ResolvedSerial:
-                    self.stats.conflicts_resolved += 1
-                    self.log("conflict resolved oid=%s"
-                             % oid_repr(oid), BLATHER)
-                    self.serials.append(oid)
+            if serial != b"\0\0\0\0\0\0\0\0":
+                self.invalidated.append(oid)
 
     def _restore(self, oid, serial, data, prev_txn):
         self.storage.restore(oid, serial, data, '', prev_txn,
@@ -697,6 +712,7 @@ def __init__(self, addr, storages,
                  invalidation_age=None,
                  transaction_timeout=None,
                  ssl=None,
+                 client_conflict_resolution=False,
                  ):
         """StorageServer constructor.
 
@@ -767,15 +783,23 @@ def __init__(self, addr, storages,
         for name, storage in storages.items():
             self._setup_invq(name, storage)
             storage.registerDB(StorageServerDB(self, name))
+            if client_conflict_resolution:
+                # XXX this may go away later, when storages grow
+                # configuration for this.
+                storage.tryToResolveConflict = never_resolve_conflict
         self.invalidation_age = invalidation_age
         self.zeo_storages_by_storage_id = {} # {storage_id -> [ZEOStorage]}
-        self.acceptor = Acceptor(self, addr, ssl)
-        if isinstance(addr, tuple) and addr[0]:
-            self.addr = self.acceptor.addr
-        else:
-            self.addr = addr
-        self.loop = self.acceptor.loop
-        ZODB.event.notify(Serving(self, address=self.acceptor.addr))
+        self.client_conflict_resolution = client_conflict_resolution
+
+        if addr is not None:
+            self.acceptor = Acceptor(self, addr, ssl)
+            if isinstance(addr, tuple) and addr[0]:
+                self.addr = self.acceptor.addr
+            else:
+                self.addr = addr
+            self.loop = self.acceptor.loop
+            ZODB.event.notify(Serving(self, address=self.acceptor.addr))
+
         self.stats = {}
         self.timeouts = {}
         for name in self.storages.keys():
@@ -1308,3 +1332,8 @@ class Serving(ServerEvent):
 
 class Closed(ServerEvent):
     pass
+
+def never_resolve_conflict(oid, committedSerial, oldSerial, newpickle,
+                           committedData=b''):
+    raise ConflictError(oid=oid, serials=(committedSerial, oldSerial),
+                        data=newpickle)

src/ZEO/TransactionBuffer.py

@@ -46,7 +46,8 @@ def __init__(self, connection_generation):
         # stored are builtin types -- strings or None.
         self.pickler = Pickler(self.file, 1)
         self.pickler.fast = 1
-        self.resolved = set() # {oid}
+        self.server_resolved = set() # {oid}
+        self.client_resolved = {} # {oid -> buffer_record_number}
         self.exception = None
 
     def close(self):
@@ -59,19 +60,26 @@ def store(self, oid, data):
         # Estimate per-record cache size
         self.size = self.size + (data and len(data) or 0) + 31
 
+    def resolve(self, oid, data):
+        """Record client-resolved data
+        """
+        self.store(oid, data)
+        self.client_resolved[oid] = self.count - 1
+
     def serial(self, oid, serial):
         if isinstance(serial, Exception):
             self.exception = serial # This transaction will never be committed
         elif serial == ResolvedSerial:
-            self.resolved.add(oid)
+            self.server_resolved.add(oid)
 
     def storeBlob(self, oid, blobfilename):
         self.blobs.append((oid, blobfilename))
 
     def __iter__(self):
         self.file.seek(0)
         unpickler = Unpickler(self.file)
-        resolved = self.resolved
+        server_resolved = self.server_resolved
+        client_resolved = self.client_resolved
 
         # Gaaaa, this is awkward. There can be entries in serials that
         # aren't in the buffer, because undo.  Entries can be repeated
@@ -81,10 +89,11 @@ def __iter__(self):
         seen = set()
         for i in range(self.count):
             oid, data = unpickler.load()
-            seen.add(oid)
-            yield oid, data, oid in resolved
+            if client_resolved.get(oid, i) == i:
+                seen.add(oid)
+                yield oid, data, oid in server_resolved
 
         # We may have leftover oids because undo
-        for oid in resolved:
+        for oid in server_resolved:
             if oid not in seen:
                 yield oid, None, True

src/ZEO/runzeo.py

@@ -98,6 +98,9 @@ def add_zeo_options(self):
         self.add("address", "zeo.address.address",
                  required="no server address specified; use -a or -C")
         self.add("read_only", "zeo.read_only", default=0)
+        self.add("client_conflict_resolution",
+                 "zeo.client_conflict_resolution",
+                 default=0)
         self.add("invalidation_queue_size", "zeo.invalidation_queue_size",
                  default=100)
         self.add("invalidation_age", "zeo.invalidation_age")
@@ -339,6 +342,7 @@ def create_server(storages, options):
         options.address,
         storages,
         read_only = options.read_only,
+        client_conflict_resolution=options.client_conflict_resolution,
         invalidation_queue_size = options.invalidation_queue_size,
         invalidation_age = options.invalidation_age,
         transaction_timeout = options.transaction_timeout,

src/ZEO/server.xml

@@ -107,6 +107,14 @@
       <metadefault>$INSTANCE/var/ZEO.pid (or $clienthome/ZEO.pid)</metadefault>
     </key>
 
+    <key name="client-conflict-resolution" datatype="boolean"
+         required="no" default="false">
+      <description>
+        Flag indicating whether the server should return conflict
+        errors to the client, for resolution there.
+      </description>
+    </key>
+
   </sectiontype>
 
 </component>

src/ZEO/tests/CommitLockTests.py

@@ -30,6 +30,8 @@ class DummyDB:
     def invalidate(self, *args, **kwargs):
         pass
 
+    transform_record_data = untransform_record_data = lambda self, data: data
+
 class WorkerThread(TestThread):
 
     # run the entire test in a thread so that the blocking call for

src/ZEO/tests/ConnectionTests.py

@@ -59,6 +59,9 @@ def invalidate(self, *args, **kwargs):
     def invalidateCache(self):
         pass
 
+    transform_record_data = untransform_record_data = lambda self, data: data
+
+
 class CommonSetupTearDown(StorageTestBase):
     """Common boilerplate"""
 

src/ZEO/tests/forker.py

@@ -33,7 +33,7 @@
 class ZEOConfig:
     """Class to generate ZEO configuration file. """
 
-    def __init__(self, addr):
+    def __init__(self, addr, **options):
         if isinstance(addr, str):
             self.logpath = addr+'.log'
         else:
@@ -42,6 +42,7 @@ def __init__(self, addr):
         self.address = addr
         self.read_only = None
         self.loglevel = 'INFO'
+        self.__dict__.update(options)
 
     def dump(self, f):
         print("<zeo>", file=f)
@@ -52,7 +53,7 @@ def dump(self, f):
         for name in (
             'invalidation_queue_size', 'invalidation_age',
             'transaction_timeout', 'pid_filename',
-            'ssl_certificate', 'ssl_key',
+            'ssl_certificate', 'ssl_key', 'client_conflict_resolution',
             ):
             v = getattr(self, name, None)
             if v:
@@ -159,7 +160,7 @@ def stop_runner(thread, config, qin, qout, stop_timeout=9, pid=None):
         # The runner thread didn't stop. If it was a process,
         # give it some time to exit
         if hasattr(thread, 'pid') and thread.pid:
-            os.waitpid(thread.pid)
+            os.waitpid(thread.pid, 0)
         else:
             # Gaaaa, force gc in hopes of maybe getting the unclosed
             # sockets to get GCed

src/ZEO/tests/testConversionSupport.py

@@ -52,6 +52,8 @@ class FakeServer:
     def register_connection(*args):
         return None, None
 
+    client_conflict_resolution = False
+
 class FakeConnection:
     protocol_version = b'Z4'
     addr = 'test'