Github user smarthi commented on a diff in the pull request:
https://github.com/apache/incubator-streams/pull/345#discussion_r94086200
--- Diff:
streams-contrib/streams-persist-cassandra/src/main/java/org/apache/streams/cassandra/CassandraPersistReader.java
---
@@ -0,0 +1,316 @@
+/*
+ * 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
+ *
+ * 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 org.apache.streams.cassandra;
+
+import org.apache.streams.config.ComponentConfigurator;
+import org.apache.streams.config.StreamsConfigurator;
+import org.apache.streams.core.DatumStatusCounter;
+import org.apache.streams.core.StreamsDatum;
+import org.apache.streams.core.StreamsPersistReader;
+import org.apache.streams.core.StreamsResultSet;
+import org.apache.streams.jackson.StreamsJacksonMapper;
+
+import com.datastax.driver.core.Cluster;
+import com.datastax.driver.core.DataType;
+import com.datastax.driver.core.KeyspaceMetadata;
+import com.datastax.driver.core.Metadata;
+import com.datastax.driver.core.ResultSet;
+import com.datastax.driver.core.Row;
+import com.datastax.driver.core.Session;
+import com.datastax.driver.core.TableMetadata;
+import com.datastax.driver.core.querybuilder.QueryBuilder;
+import com.datastax.driver.core.schemabuilder.SchemaBuilder;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.google.common.collect.Queues;
+import org.apache.commons.lang3.StringUtils;
+import org.joda.time.DateTime;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.math.BigInteger;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Queue;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * CassandraPersistReader reads documents from cassandra.
+ */
+public class CassandraPersistReader implements StreamsPersistReader {
+
+ public static final String STREAMS_ID = "CassandraPersistReader";
+
+ public static final Logger LOGGER =
LoggerFactory.getLogger(CassandraPersistReader.class);
+
+ protected volatile Queue<StreamsDatum> persistQueue;
+
+ private ObjectMapper mapper = StreamsJacksonMapper.getInstance();
+
+ private ExecutorService executor;
+ private CompletableFuture<Boolean> readerTaskFuture = new
CompletableFuture<>();
+
+ private CassandraConfiguration config;
+
+ protected Cluster cluster;
+ protected Session session;
+
+ protected String keyspace;
+ protected String table;
+ protected Iterator<Row> rowIterator;
+
+ protected final ReadWriteLock lock = new ReentrantReadWriteLock();
+
+ /**
+ * CassandraPersistReader constructor - resolves CassandraConfiguration
from JVM 'cassandra'.
+ */
+ public CassandraPersistReader() {
+ this.config = new ComponentConfigurator<>(CassandraConfiguration.class)
+
.detectConfiguration(StreamsConfigurator.getConfig().getConfig("cassandra"));
+ }
+
+ /**
+ * CassandraPersistReader constructor - uses supplied
CassandraConfiguration.
+ * @param config config
+ */
+ public CassandraPersistReader(CassandraConfiguration config) {
+ this.config = config;
+ }
+
+ /**
+ * CassandraPersistReader constructor - uses supplied persistQueue.
+ * @param persistQueue persistQueue
+ */
+ public CassandraPersistReader(Queue<StreamsDatum> persistQueue) {
+ this.config = new ComponentConfigurator<>(CassandraConfiguration.class)
+
.detectConfiguration(StreamsConfigurator.getConfig().getConfig("cassandra"));
+ this.persistQueue = persistQueue;
+ }
+
+ public void setPersistQueue(Queue<StreamsDatum> persistQueue) {
+ this.persistQueue = persistQueue;
+ }
+
+ public Queue<StreamsDatum> getPersistQueue() {
+ return persistQueue;
+ }
+
+ public void stop() {
+ }
+
+ @Override
+ public String getId() {
+ return STREAMS_ID;
+ }
+
+ @Override
+ public void prepare(Object configurationObject) {
+ connectToCassandra();
+
+ String selectStatement = getSelectStatement();
+ ResultSet rs = session.execute(selectStatement);
+ rowIterator = rs.iterator();
+
+ if (!rowIterator.hasNext()) {
+ throw new RuntimeException("Table" + table + "is empty!");
+ }
+
+ persistQueue = constructQueue();
+
+ executor = Executors.newSingleThreadExecutor();
+ }
+
+ @Override
+ public void cleanUp() {
+ stop();
+ }
+
+ protected StreamsDatum prepareDatum(Row row) {
+ ObjectNode objectNode;
+
+ try {
+ byte[] value = row.getBytes(config.getColumn()).array();
+ objectNode = mapper.readValue(value, ObjectNode.class);
+ } catch (IOException ex) {
+ LOGGER.warn("document isn't valid JSON.");
+ return null;
+ }
+
+ return new StreamsDatum(objectNode);
+ }
+
+ private synchronized void connectToCassandra() {
+ Cluster.Builder clusterBuilder = Cluster.builder()
+ .addContactPoints(config.getHost().toArray(new
String[config.getHost().size()]))
+ .withPort(config.getPort().intValue());
+
+ keyspace = config.getKeyspace();
+ table = config.getTable();
+
+ if (StringUtils.isNotEmpty(config.getUser()) &&
StringUtils.isNotEmpty(config.getPassword())) {
+ cluster = clusterBuilder.withCredentials(config.getUser(),
config.getPassword()).build();
+ } else {
+ cluster = clusterBuilder.build();
+ }
+
+ Metadata metadata = cluster.getMetadata();
+ if (Objects.isNull(metadata.getKeyspace(keyspace))) {
+ LOGGER.info("Keyspace {} does not exist. Creating Keyspace",
keyspace);
+ Map<String, Object> replication = new HashMap<>();
+ replication.put("class", "SimpleStrategy");
+ replication.put("replication_factor", 1);
+
+ String createKeyspaceStmt =
SchemaBuilder.createKeyspace(keyspace).with()
+ .replication(replication).getQueryString();
+ cluster.connect().execute(createKeyspaceStmt);
+ }
+
+ session = cluster.connect(keyspace);
+
+ KeyspaceMetadata ks = metadata.getKeyspace(keyspace);
+ TableMetadata tableMetadata = ks.getTable(table);
+
+ if (Objects.isNull(tableMetadata)) {
+ LOGGER.info("Table {} does not exist in Keyspace {}. Creating
Table", table, keyspace);
+ String createTableStmt = SchemaBuilder.createTable(table)
+
.addPartitionKey(config.getPartitionKeyColumn(), DataType.varchar())
+ .addColumn(config.getColumn(),
DataType.blob()).getQueryString();
+
+ session.execute(createTableStmt);
+ }
+ }
+
+ @Override
+ public StreamsResultSet readAll() {
+ ResultSet rs = session.execute(getSelectStatement());
+ Iterator<Row> rowsIterator = rs.iterator();
+
+ while (rowsIterator.hasNext()) {
+ Row row = rowsIterator.next();
+ StreamsDatum datum = prepareDatum(row);
+ write(datum);
+ }
+
+ return readCurrent();
+ }
+
+ @Override
+ public void startStream() {
+ LOGGER.debug("startStream");
+ CassandraPersistReaderTask readerTask = new
CassandraPersistReaderTask(this);
+
+ CompletableFuture.runAsync(readerTask, executor);
+
+ try {
+ if (readerTaskFuture.get()) {
+ executor.shutdown();
+ }
+ } catch (InterruptedException ex) {
+ LOGGER.trace("Interrupt", ex);
+ } catch (ExecutionException ex) {
+ LOGGER.trace("Execution exception", ex);
+ }
+ }
+
+ @Override
+ public StreamsResultSet readCurrent() {
+
+ StreamsResultSet current;
+
+ try {
+ lock.writeLock().lock();
+ current = new StreamsResultSet(persistQueue);
+ current.setCounter(new DatumStatusCounter());
+ persistQueue = constructQueue();
+ } finally {
+ lock.writeLock().unlock();
+ }
+
+ return current;
+ }
+
+ protected void write(StreamsDatum entry) {
+ boolean success;
+ do {
+ try {
+ lock.readLock().lock();
+ success = persistQueue.offer(entry);
+ Thread.yield();
+ } finally {
+ lock.readLock().unlock();
+ }
+ }
+ while (!success);
+ }
+
+ @Override
+ public StreamsResultSet readNew(BigInteger sequence) {
+ return null;
+ }
+
+ @Override
+ public StreamsResultSet readRange(DateTime start, DateTime end) {
+ return null;
+ }
+
+ @Override
+ public boolean isRunning() {
+ return !executor.isTerminated() || !executor.isShutdown();
+ }
+
+ private Queue<StreamsDatum> constructQueue() {
+ return Queues.synchronizedQueue(new
LinkedBlockingQueue<StreamsDatum>(10000));
--- End diff --
Question: does the Queue need to be synchronized if not using any of the
bulk Queue API ?
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