[GitHub] [cassandra-accord] bdeggleston commented on a diff in pull request #49: Bootstrap tcm integration

["bdeggleston (via GitHub)" <gi...@apache.org>]

bdeggleston commented on code in PR #49:
URL: https://github.com/apache/cassandra-accord/pull/49#discussion_r1222263945


##########
accord-core/src/main/java/accord/impl/AbstractConfigurationService.java:
##########
@@ -0,0 +1,337 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package accord.impl;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.primitives.Ints;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import accord.api.ConfigurationService;
+import accord.local.Node;
+import accord.topology.Topology;
+import accord.utils.Invariants;
+import accord.utils.async.AsyncResult;
+import accord.utils.async.AsyncResults;
+
+public abstract class AbstractConfigurationService<EpochState extends AbstractConfigurationService.AbstractEpochState,
+                                                   EpochHistory extends AbstractConfigurationService.AbstractEpochHistory<EpochState>>
+                      implements ConfigurationService
+{
+    private static final Logger logger = LoggerFactory.getLogger(AbstractConfigurationService.class);
+
+    protected final Node.Id localId;
+
+    protected final EpochHistory epochs = createEpochHistory();
+
+    protected final List<Listener> listeners = new ArrayList<>();
+
+    public abstract static class AbstractEpochState
+    {
+        protected final long epoch;
+        protected final AsyncResult.Settable<Topology> received = AsyncResults.settable();
+        protected final AsyncResult.Settable<Void> acknowledged = AsyncResults.settable();
+        protected AsyncResult<Void> reads = null;
+
+        protected Topology topology = null;
+
+        public AbstractEpochState(long epoch)
+        {
+            this.epoch = epoch;
+        }
+
+        public long epoch()
+        {
+            return epoch;
+        }
+
+        @Override
+        public String toString()
+        {
+            return "EpochState{" + epoch + '}';
+        }
+    }
+
+    @VisibleForTesting
+    public abstract static class AbstractEpochHistory<EpochState extends AbstractEpochState>
+    {
+        // TODO (low priority): move pendingEpochs / FetchTopology into here?
+        private List<EpochState> epochs = new ArrayList<>();
+
+        protected long lastReceived = 0;
+        protected long lastAcknowledged = 0;
+
+        protected abstract EpochState createEpochState(long epoch);
+
+        public long minEpoch()
+        {
+            return epochs.isEmpty() ? 0L : epochs.get(0).epoch;
+        }
+
+        public long maxEpoch()
+        {
+            int size = epochs.size();
+            return size == 0 ? 0L : epochs.get(size - 1).epoch;
+        }
+
+        @VisibleForTesting
+        EpochState atIndex(int idx)
+        {
+            return epochs.get(idx);
+        }
+
+        @VisibleForTesting
+        int size()
+        {
+            return epochs.size();
+        }
+
+        EpochState getOrCreate(long epoch)
+        {
+            Invariants.checkArgument(epoch > 0);
+            if (epochs.isEmpty())
+            {
+                EpochState state = createEpochState(epoch);
+                epochs.add(state);
+                return state;
+            }
+
+            long minEpoch = minEpoch();
+            if (epoch < minEpoch)
+            {
+                int prepend = Ints.checkedCast(minEpoch - epoch);
+                List<EpochState> next = new ArrayList<>(epochs.size() + prepend);
+                for (long addEpoch=epoch; addEpoch<minEpoch; addEpoch++)
+                    next.add(createEpochState(addEpoch));
+                next.addAll(epochs);
+                epochs = next;
+                minEpoch = minEpoch();
+                Invariants.checkState(minEpoch == epoch);
+            }
+            long maxEpoch = maxEpoch();
+            int idx = Ints.checkedCast(epoch - minEpoch);
+
+            // add any missing epochs
+            for (long addEpoch = maxEpoch + 1; addEpoch <= epoch; addEpoch++)
+                epochs.add(createEpochState(addEpoch));
+
+            return epochs.get(idx);
+        }
+
+        public void receive(Topology topology)
+        {
+            long epoch = topology.epoch();
+            Invariants.checkState(lastReceived == epoch - 1 || epoch == 0 || lastReceived == 0);
+            lastReceived = epoch;
+            EpochState state = getOrCreate(epoch);
+            if (state != null)
+            {
+                state.topology = topology;
+                state.received.setSuccess(topology);
+            }
+        }
+
+        AsyncResult<Topology> receiveFuture(long epoch)
+        {
+            return getOrCreate(epoch).received;
+        }
+
+        Topology topologyFor(long epoch)
+        {
+            return getOrCreate(epoch).topology;
+        }
+
+        public void acknowledge(EpochReady ready)
+        {
+            long epoch = ready.epoch;
+            Invariants.checkState(lastAcknowledged == epoch - 1 || epoch == 0 || lastAcknowledged == 0);
+            lastAcknowledged = epoch;
+            EpochState state = getOrCreate(epoch);
+            state.reads = ready.reads;

Review Comment:
   The parent class synchronizes access, though EpochState is extensible by subclasses of AbstractConfigurationService



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