Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/17902#discussion_r119412048
--- Diff:
common/kvstore/src/main/java/org/apache/spark/kvstore/LevelDB.java ---
@@ -0,0 +1,303 @@
+/*
+ * 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 org.apache.spark.kvstore;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.atomic.AtomicReference;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.Objects;
+import com.google.common.base.Preconditions;
+import com.google.common.base.Throwables;
+import org.fusesource.leveldbjni.JniDBFactory;
+import org.iq80.leveldb.DB;
+import org.iq80.leveldb.Options;
+import org.iq80.leveldb.WriteBatch;
+
+/**
+ * Implementation of KVStore that uses LevelDB as the underlying data
store.
+ */
+public class LevelDB implements KVStore {
+
+ @VisibleForTesting
+ static final long STORE_VERSION = 1L;
+
+ @VisibleForTesting
+ static final byte[] STORE_VERSION_KEY = "__version__".getBytes(UTF_8);
+
+ /** DB key where app metadata is stored. */
+ private static final byte[] METADATA_KEY = "__meta__".getBytes(UTF_8);
+
+ /** DB key where type aliases are stored. */
+ private static final byte[] TYPE_ALIASES_KEY =
"__types__".getBytes(UTF_8);
+
+ final AtomicReference<DB> _db;
+ final KVStoreSerializer serializer;
+
+ private final ConcurrentMap<String, byte[]> typeAliases;
+ private final ConcurrentMap<Class<?>, LevelDBTypeInfo> types;
+
+ public LevelDB(File path) throws Exception {
+ this(path, new KVStoreSerializer());
+ }
+
+ public LevelDB(File path, KVStoreSerializer serializer) throws Exception
{
+ this.serializer = serializer;
+ this.types = new ConcurrentHashMap<>();
+
+ Options options = new Options();
+ options.createIfMissing(!path.exists());
+ this._db = new AtomicReference<>(JniDBFactory.factory.open(path,
options));
+
+ byte[] versionData = db().get(STORE_VERSION_KEY);
+ if (versionData != null) {
+ long version = serializer.deserializeLong(versionData);
+ if (version != STORE_VERSION) {
+ throw new UnsupportedStoreVersionException();
+ }
+ } else {
+ db().put(STORE_VERSION_KEY, serializer.serialize(STORE_VERSION));
+ }
+
+ Map<String, byte[]> aliases;
+ try {
+ aliases = get(TYPE_ALIASES_KEY, TypeAliases.class).aliases;
+ } catch (NoSuchElementException e) {
+ aliases = new HashMap<>();
+ }
+ typeAliases = new ConcurrentHashMap<>(aliases);
+ }
+
+ @Override
+ public <T> T getMetadata(Class<T> klass) throws Exception {
+ try {
+ return get(METADATA_KEY, klass);
+ } catch (NoSuchElementException nsee) {
+ return null;
+ }
+ }
+
+ @Override
+ public void setMetadata(Object value) throws Exception {
+ if (value != null) {
+ put(METADATA_KEY, value);
+ } else {
+ db().delete(METADATA_KEY);
+ }
+ }
+
+ <T> T get(byte[] key, Class<T> klass) throws Exception {
+ byte[] data = db().get(key);
+ if (data == null) {
+ throw new NoSuchElementException(new String(key, UTF_8));
+ }
+ return serializer.deserialize(data, klass);
+ }
+
+ private void put(byte[] key, Object value) throws Exception {
+ Preconditions.checkArgument(value != null, "Null values are not
allowed.");
+ db().put(key, serializer.serialize(value));
+ }
+
+ @Override
+ public <T> T read(Class<T> klass, Object naturalKey) throws Exception {
+ Preconditions.checkArgument(naturalKey != null, "Null keys are not
allowed.");
+ byte[] key = getTypeInfo(klass).naturalIndex().start(null, naturalKey);
+ return get(key, klass);
+ }
+
+ @Override
+ public void write(Object value) throws Exception {
+ Preconditions.checkArgument(value != null, "Null values are not
allowed.");
+ LevelDBTypeInfo ti = getTypeInfo(value.getClass());
+
+ try (WriteBatch batch = db().createWriteBatch()) {
+ byte[] data = serializer.serialize(value);
+ synchronized (ti) {
+ Object existing;
+ try {
+ existing = get(ti.naturalIndex().entityKey(null, value),
value.getClass());
+ } catch (NoSuchElementException e) {
+ existing = null;
+ }
+
+ PrefixCache cache = new PrefixCache(value);
+ byte[] naturalKey =
ti.naturalIndex().toKey(ti.naturalIndex().getValue(value));
--- End diff --
if the key is null, I guess this will complain somewhere in here, but a
nicer error msg would be better.
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