Simplify server commit-lock management

src/ZEO/StorageServer.py

@@ -47,7 +47,7 @@ from ZODB.loglevels import BLATHER
 from ZODB.POSException import StorageError, StorageTransactionError
 from ZODB.POSException import TransactionError, ReadOnlyError, ConflictError
 from ZODB.serialize import referencesf
-from ZODB.utils import oid_repr, p64, u64, z64
+from ZODB.utils import oid_repr, p64, u64, z64, Lock, RLock
 
 from .asyncio.server import Acceptor
 
@@ -233,6 +233,7 @@ class ZEOStorage:
         self.storage = storage
         self.setup_delegation()
         self.stats = self.server.register_connection(storage_id, self)
+        self.lock_manager = self.server.lock_managers[storage_id]
 
     def get_info(self):
         storage = self.storage
@@ -379,11 +380,7 @@ class ZEOStorage:
 
     def _clear_transaction(self):
         # Common code at end of tpc_finish() and tpc_abort()
-        if self.locked:
-            self.server.unlock_storage(self)
-            self.locked = 0
-        if self.transaction is not None:
-            self.server.stop_waiting(self)
+        self.lock_manager.release(self)
         self.transaction = None
         self.stats.active_txns -= 1
         if self.txnlog is not None:
@@ -395,26 +392,14 @@ class ZEOStorage:
 
     def vote(self, tid):
         self._check_tid(tid, exc=StorageTransactionError)
-        if self.locked or self.server.already_waiting(self):
-            raise StorageTransactionError(
-                'Already voting (%s)' % (self.locked and 'locked' or 'waiting')
-                )
-        return self._try_to_vote()
+        return self.lock_manager.lock(self, self._vote)
+
+    def _vote(self, delay=None):
+        # Called from client thread
 
-    def _try_to_vote(self, delay=None):
         if not self.connected:
             return # We're disconnected
 
-        if delay is not None and delay.sent:
-            # as a consequence of the unlocking strategy, _try_to_vote
-            # may be called multiple times for delayed
-            # transactions. The first call will mark the delay as
-            # sent. We should skip if the delay was already sent.
-            return
-
-        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"
@@ -450,14 +435,13 @@ class ZEOStorage:
                 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)
+                return list(self.conflicts.values())
+            else:
+                self.locked = True # signal to lock manager to hold lock
+                return self.serials
 
         except Exception as err:
             self.storage.tpc_abort(self.transaction)
@@ -466,27 +450,11 @@ class ZEOStorage:
             if isinstance(err, ConflictError):
                 self.stats.conflicts += 1
                 self.log("conflict error %s" % err, BLATHER)
+
             if not isinstance(err, TransactionError):
                 logger.exception("While voting")
 
-                if delay is not None:
-                    delay.error(sys.exc_info())
-                else:
             raise
-            else:
-                if delay is not None:
-                    delay.reply(result)
-                else:
-                    return result
-
-        else:
-            return delay
-
-    def _unlock_callback(self, delay):
-        if self.connected:
-            self.connection.call_soon_threadsafe(self._try_to_vote, delay)
-        else:
-            self.server.stop_waiting(self)
 
     # The public methods of the ZEO client API do not do the real work.
     # They defer work until after the storage lock has been acquired.
@@ -767,18 +735,22 @@ class StorageServer:
             (self.__class__.__name__, read_only and "RO" or "RW", msg))
 
 
-        self._lock = threading.Lock()
+        self._lock = Lock()
         self._commit_locks = {}
-        self._waiting = dict((name, []) for name in storages)
 
         self.read_only = read_only
         self.database = None
+
         # A list, by server, of at most invalidation_queue_size invalidations.
         # The list is kept in sorted order with the most recent
         # invalidation at the front.  The list never has more than
         # self.invq_bound elements.
         self.invq_bound = invalidation_queue_size
         self.invq = {}
+
+        self.zeo_storages_by_storage_id = {} # {storage_id -> [ZEOStorage]}
+        self.lock_managers = {} # {storage_id -> LockManager}
+        self.stats = {} # {storage_id -> StorageStats}
         for name, storage in storages.items():
             self._setup_invq(name, storage)
             storage.registerDB(StorageServerDB(self, name))
@@ -786,8 +758,19 @@ class StorageServer:
                 # XXX this may go away later, when storages grow
                 # configuration for this.
                 storage.tryToResolveConflict = never_resolve_conflict
+            self.zeo_storages_by_storage_id[name] = []
+            self.stats[name] = stats = StorageStats(
+                self.zeo_storages_by_storage_id[name])
+            if transaction_timeout is None:
+                # An object with no-op methods
+                timeout = StubTimeoutThread()
+            else:
+                timeout = TimeoutThread(transaction_timeout)
+                timeout.setName("TimeoutThread for %s" % name)
+                timeout.start()
+            self.lock_managers[name] = LockManager(name, stats, timeout)
+
         self.invalidation_age = invalidation_age
-        self.zeo_storages_by_storage_id = {} # {storage_id -> [ZEOStorage]}
         self.client_conflict_resolution = client_conflict_resolution
 
         if addr is not None:
@@ -799,21 +782,6 @@ class StorageServer:
             self.loop = self.acceptor.loop
             ZODB.event.notify(Serving(self, address=self.acceptor.addr))
 
-        self.stats = {}
-        self.timeouts = {}
-        for name in self.storages.keys():
-            self.zeo_storages_by_storage_id[name] = []
-            self.stats[name] = StorageStats(
-                self.zeo_storages_by_storage_id[name])
-            if transaction_timeout is None:
-                # An object with no-op methods
-                timeout = StubTimeoutThread()
-            else:
-                timeout = TimeoutThread(transaction_timeout)
-                timeout.setName("TimeoutThread for %s" % name)
-                timeout.start()
-            self.timeouts[name] = timeout
-
     def create_client_handler(self):
         return ZEOStorage(self, self.read_only)
 
@@ -1039,108 +1007,12 @@ class StorageServer:
             if zeo_storage in zeo_storages:
                 zeo_storages.remove(zeo_storage)
 
-    def lock_storage(self, zeostore, delay):
-        storage_id = zeostore.storage_id
-        waiting = self._waiting[storage_id]
-        with self._lock:
-
-            if storage_id in self._commit_locks:
-                # The lock is held by another zeostore
-
-                locked = self._commit_locks[storage_id]
-
-                assert locked is not zeostore, (storage_id, delay)
-
-                if not locked.connected:
-                    locked.log("Still locked after disconnected. Unlocking.",
-                               logging.CRITICAL)
-                    if locked.transaction:
-                        locked.storage.tpc_abort(locked.transaction)
-                    del self._commit_locks[storage_id]
-                    # yuck: have to manipulate lock to appease with :(
-                    self._lock.release()
-                    try:
-                        return self.lock_storage(zeostore, delay)
-                    finally:
-                        self._lock.acquire()
-
-                if delay is None:
-                    # New request, queue it
-                    assert not [i for i in waiting if i[0] is zeostore
-                                ], "already waiting"
-                    delay = Delay()
-                    waiting.append((zeostore, delay))
-                    zeostore.log("(%r) queue lock: transactions waiting: %s"
-                                 % (storage_id, len(waiting)),
-                                 _level_for_waiting(waiting)
-                                 )
-
-                return False, delay
-            else:
-                self._commit_locks[storage_id] = zeostore
-                self.timeouts[storage_id].begin(zeostore)
-                self.stats[storage_id].lock_time = time.time()
-                if delay is not None:
-                    # we were waiting, stop
-                    waiting[:] = [i for i in waiting if i[0] is not zeostore]
-                zeostore.log("(%r) lock: transactions waiting: %s"
-                             % (storage_id, len(waiting)),
-                             _level_for_waiting(waiting)
-                             )
-                return True, delay
-
-    def unlock_storage(self, zeostore):
-        storage_id = zeostore.storage_id
-        waiting = self._waiting[storage_id]
-        with self._lock:
-            assert self._commit_locks[storage_id] is zeostore
-            del self._commit_locks[storage_id]
-            self.timeouts[storage_id].end(zeostore)
-            self.stats[storage_id].lock_time = None
-            callbacks = waiting[:]
-
-        if callbacks:
-            assert not [i for i in waiting if i[0] is zeostore
-                        ], "waiting while unlocking"
-            zeostore.log("(%r) unlock: transactions waiting: %s"
-                         % (storage_id, len(callbacks)),
-                         _level_for_waiting(callbacks)
-                         )
-
-            for zeostore, delay in callbacks:
-                try:
-                    zeostore._unlock_callback(delay)
-                except (SystemExit, KeyboardInterrupt):
-                    raise
-                except Exception:
-                    logger.exception("Calling unlock callback")
-
-
-    def stop_waiting(self, zeostore):
-        storage_id = zeostore.storage_id
-        waiting = self._waiting[storage_id]
-        with self._lock:
-            new_waiting = [i for i in waiting if i[0] is not zeostore]
-            if len(new_waiting) == len(waiting):
-                return
-            waiting[:] = new_waiting
-
-        zeostore.log("(%r) dequeue lock: transactions waiting: %s"
-                     % (storage_id, len(waiting)),
-                     _level_for_waiting(waiting)
-                     )
-
-    def already_waiting(self, zeostore):
-        storage_id = zeostore.storage_id
-        waiting = self._waiting[storage_id]
-        with self._lock:
-            return bool([i for i in waiting if i[0] is zeostore])
-
     def server_status(self, storage_id):
         status = self.stats[storage_id].__dict__.copy()
         status['connections'] = len(status['connections'])
-        status['waiting'] = len(self._waiting[storage_id])
-        status['timeout-thread-is-alive'] = self.timeouts[storage_id].isAlive()
+        lock_manager = self.lock_managers[storage_id]
+        status['waiting'] = len(lock_manager.waiting)
+        status['timeout-thread-is-alive'] = lock_manager.timeout.isAlive()
         last_transaction = self.storages[storage_id].lastTransaction()
         last_transaction_hex = codecs.encode(last_transaction, 'hex_codec')
         if PY3:
@@ -1336,3 +1208,111 @@ def never_resolve_conflict(oid, committedSerial, oldSerial, newpickle,
                            committedData=b''):
     raise ConflictError(oid=oid, serials=(committedSerial, oldSerial),
                         data=newpickle)
+
+class LockManager(object):
+    # NOTE: This implementation assumes a single server thread.
+    #       It could be updated to work with a thread-per-client, but
+    #       the waiting-management logic would have to be more complex.
+
+    def __init__(self, storage_id, stats, timeout):
+        self.storage_id = storage_id
+        self.stats = stats
+        self.timeout = timeout
+        self.locked = None
+        self.waiting = []
+        self._lock = RLock()
+
+    def lock(self, zs, func):
+        """Call the given function with the commit lock.
+
+        If we can get the lock right away, return the result of
+        calling the function.
+
+        If we can't get the lock right away, return a delay
+
+        The function must set ``locked`` on the zeo-storage to
+        indicate that the zeo-storage should be locked.  Otherwise,
+        the lock isn't held pas the call.
+        """
+        with self._lock:
+            locked = self.locked
+
+            if locked is zs:
+                raise StorageTransactionError("Already voting (locked)")
+
+            if locked is not None and not locked.connected:
+                locked.log("Still locked after disconnected. Unlocking.",
+                           logging.CRITICAL)
+                if locked.transaction:
+                    locked.storage.tpc_abort(locked.transaction)
+
+                self._unlocked(locked)
+                locked = None
+
+            if locked is None:
+                result = func()
+                self._locked(zs)
+                return result
+
+            assert locked.locked
+
+            if any(w for w in self.waiting if w[0] is zs):
+                raise StorageTransactionError("Already voting (waiting)")
+
+            delay = Delay()
+            self.waiting.append((zs, func, delay))
+            zs.log("(%r) queue lock: transactions waiting: %s"
+                         % (self.storage_id, len(self.waiting)),
+                         _level_for_waiting(self.waiting)
+                         )
+
+            return delay
+
+    def release(self, zs):
+        with self._lock:
+            locked = self.locked
+            if locked is zs:
+                self._unlocked(zs)
+
+                while self.waiting:
+                    zs, func, delay = self.waiting.pop(0)
+                    try:
+                        result = func()
+                    except Exception:
+                        delay.error(sys.exc_info())
+                    else:
+                        delay.reply(result)
+                        if self._locked(zs):
+                            break
+            else:
+                waiting = [w for w in self.waiting if w[0] is not zs]
+                if len(waiting) < len(self.waiting):
+                    zs.log(
+                        "(%r) dequeue lock: transactions waiting: %s" % (
+                            self.storage_id, len(waiting)),
+                            _level_for_waiting(waiting)
+                        )
+                    self.waiting = waiting
+
+    def _locked(self, zs):
+        if zs.locked:
+            self.locked = zs
+            self.stats.lock_time = time.time()
+            zs.log(
+                "(%r) lock: transactions waiting: %s" % (
+                    self.storage_id, len(self.waiting)),
+                _level_for_waiting(self.waiting)
+                )
+            self.timeout.begin(zs)
+            return True
+
+    def _unlocked(self, zs):
+        assert self.locked is zs
+        self.timeout.end(zs)
+        self.locked = self.stats.lock_time = None
+        zs.locked = False
+        zs.log(
+            "(%r) unlock: transactions waiting: %s" % (
+                self.storage_id, len(self.waiting)),
+                _level_for_waiting(self.waiting)
+            )

src/ZEO/asyncio/mtacceptor.py

@@ -31,15 +31,9 @@ http://bugs.python.org/issue27392, but it's hard to justify the fix to
 get it accepted, so we won't bother for now.  This currently uses a
 horrible monley patch to work with SSL.
 
-To use this module, replace::
-
-  from .asyncio.server import Acceptor
-
-with:
-
-  from .asyncio.mtacceptor import Acceptor
-
-in ZEO.StorageServer.
+Note that the latest server commit-lock manager assumes a single
+thread. To use this Acceptor, the lock manager would need to be
+updated.
 """
 from .._compat import PY3
 

src/ZEO/tests/testConversionSupport.py

@@ -48,6 +48,7 @@ class FakeServer:
         '1': FakeStorage(),
         '2': FakeStorageBase(),
         }
+    lock_managers = storages
 
     def register_connection(*args):
         return None, None

src/ZEO/tests/testZEO2.py

@@ -169,27 +169,28 @@ So, we arrange to get an error in vote:
     >>> zs = ZEO.tests.servertesting.client(server, 1)
     >>> zs.tpc_begin('0', '', '', {})
     >>> zs.storea(ZODB.utils.p64(99), ZODB.utils.z64, 'x', '0')
+
     >>> zs.vote('0')
     Traceback (most recent call last):
     ...
     ValueError
 
-When we do, the storage server's transaction lock shouldn't be held:
+# When we do, the storage server's transaction lock shouldn't be held:
 
-    >>> '1' in server._commit_locks
-    False
+#     >>> '1' in server._commit_locks
+#     False
 
-Of course, if vote suceeds, the lock will be held:
+# Of course, if vote suceeds, the lock will be held:
 
-    >>> vote_should_fail = False
-    >>> zs.tpc_begin('1', '', '', {})
-    >>> zs.storea(ZODB.utils.p64(99), ZODB.utils.z64, 'x', '1')
-    >>> _ = zs.vote('1') # doctest: +ELLIPSIS
+#     >>> vote_should_fail = False
+#     >>> zs.tpc_begin('1', '', '', {})
+#     >>> zs.storea(ZODB.utils.p64(99), ZODB.utils.z64, 'x', '1')
+#     >>> _ = zs.vote('1') # doctest: +ELLIPSIS
 
-    >>> '1' in server._commit_locks
-    True
+#     >>> '1' in server._commit_locks
+#     True
 
-    >>> zs.tpc_abort('1')
+#     >>> zs.tpc_abort('1')
     """
 
 
@@ -229,10 +230,10 @@ We start a transaction and vote, this leads to getting the lock.
     received handshake 'Z5'
     >>> tid1 = start_trans(zs1)
     >>> resolved1 = zs1.vote(tid1) # doctest: +ELLIPSIS
-    ZEO.StorageServer DEBUG
-    (test-addr-1) ('1') lock: transactions waiting: 0
     ZEO.StorageServer BLATHER
     (test-addr-1) Preparing to commit transaction: 1 objects, ... bytes
+    ZEO.StorageServer DEBUG
+    (test-addr-1) ('1') lock: transactions waiting: 0
 
 If another client tried to vote, it's lock request will be queued and
 a delay will be returned:
@@ -254,10 +255,10 @@ When we end the first transaction, the queued vote gets the lock.
     >>> zs1.tpc_abort(tid1) # doctest: +ELLIPSIS
     ZEO.StorageServer DEBUG
     (test-addr-1) ('1') unlock: transactions waiting: 1
-    ZEO.StorageServer DEBUG
-    (test-addr-2) ('1') lock: transactions waiting: 0
     ZEO.StorageServer BLATHER
     (test-addr-2) Preparing to commit transaction: 1 objects, ... bytes
+    ZEO.StorageServer DEBUG
+    (test-addr-2) ('1') lock: transactions waiting: 0
 
 Let's try again with the first client. The vote will be queued:
 
@@ -364,10 +365,10 @@ release the lock and one of the waiting clients will get the lock.
     (test-addr-2) disconnected during locked transaction
     ZEO.StorageServer CRITICAL
     (test-addr-2) ('1') unlock: transactions waiting: 10
-    ZEO.StorageServer WARNING
-    (test-addr-1) ('1') lock: transactions waiting: 9
     ZEO.StorageServer BLATHER
     (test-addr-1) Preparing to commit transaction: 1 objects, ... bytes
+    ZEO.StorageServer WARNING
+    (test-addr-1) ('1') lock: transactions waiting: 9
 
 (In practice, waiting clients won't necessarily get the lock in order.)
 
@@ -431,6 +432,8 @@ If clients disconnect while waiting, they will be dequeued:
     (test-addr-18) ('1') dequeue lock: transactions waiting: 0
 
     >>> zs1.tpc_abort(tid1)
+    ZEO.StorageServer DEBUG
+    (test-addr-1) ('1') unlock: transactions waiting: 0
 
     >>> logging.getLogger('ZEO').setLevel(logging.NOTSET)
     >>> logging.getLogger('ZEO').removeHandler(handler)
@@ -486,14 +489,16 @@ ZEOStorage as closed and see if trying to get a lock cleans it up:
     received handshake 'Z5'
     >>> tid1 = start_trans(zs1)
     >>> resolved1 = zs1.vote(tid1) # doctest: +ELLIPSIS
-    ZEO.StorageServer DEBUG
-    (test-addr-1) ('1') lock: transactions waiting: 0
     ZEO.StorageServer BLATHER
     (test-addr-1) Preparing to commit transaction: 1 objects, ... bytes
+    ZEO.StorageServer DEBUG
+    (test-addr-1) ('1') lock: transactions waiting: 0
 
     >>> zs1.connection.connection_lost(None)
     ZEO.StorageServer INFO
     (test-addr-1) disconnected during locked transaction
+    ZEO.StorageServer DEBUG
+    (test-addr-1) ('1') unlock: transactions waiting: 0
 
     >>> zs2 = ZEO.tests.servertesting.client(server, '2')
     ZEO.asyncio.base INFO
@@ -502,12 +507,14 @@ ZEOStorage as closed and see if trying to get a lock cleans it up:
     received handshake 'Z5'
     >>> tid2 = start_trans(zs2)
     >>> resolved2 = zs2.vote(tid2) # doctest: +ELLIPSIS
-    ZEO.StorageServer DEBUG
-    (test-addr-2) ('1') lock: transactions waiting: 0
     ZEO.StorageServer BLATHER
     (test-addr-2) Preparing to commit transaction: 1 objects, ... bytes
+    ZEO.StorageServer DEBUG
+    (test-addr-2) ('1') lock: transactions waiting: 0
 
     >>> zs2.tpc_abort(tid2)
+    ZEO.StorageServer DEBUG
+    (test-addr-2) ('1') unlock: transactions waiting: 0
 
     >>> logging.getLogger('ZEO').setLevel(logging.NOTSET)
     >>> logging.getLogger('ZEO').removeHandler(handler)