DATAREDIS-843 - Adapt compare-and-set to changed transaction rollback response.

We now consider a transactional rollback that returns an empty EXEC result as rollback for the CAS (compare-and-set) operation. Previously, we checked only that the response of EXEC is not null. A rollback returns an empty list which was previously considered a successful CAS operation.

The code for CAS is now extracted to CompareAndSet and is reused from RedisAtomic implementations.

Original Pull Request: #349

src/main/java/org/springframework/data/redis/support/atomic/CompareAndSet.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed 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.springframework.data.redis.support.atomic;
+
+import lombok.RequiredArgsConstructor;
+
+import java.util.Collection;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
+
+import org.springframework.dao.DataAccessException;
+import org.springframework.data.redis.core.RedisOperations;
+import org.springframework.data.redis.core.SessionCallback;
+import org.springframework.util.CollectionUtils;
+
+/**
+ * Compare-and-set (CAS) operation using Redis Transactions ({@literal WATCH} and {@literal MULTI}) to atomically update
+ * the value at {@code key}.
+ * <p>
+ * The CAS block registers a {@literal WATCH} on the key holding the expected value which guarantees that changes after
+ * watching and comparing the key will rollback the transaction. The {@literal WATCH} is reset if the comparison fails.
+ *
+ * @author Mark Paluch
+ * @since 2.0.8
+ * @see RedisAtomicDouble
+ * @see RedisAtomicInteger
+ * @see RedisAtomicLong
+ */
+@RequiredArgsConstructor
+class CompareAndSet<T> implements SessionCallback<Boolean> {
+
+	private final Supplier<T> getter;
+	private final Consumer<T> setter;
+	private final String key;
+	private final T expect;
+	private final T update;
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.redis.core.SessionCallback#execute(org.springframework.data.redis.core.RedisOperations)
+	 */
+	@Override
+	@SuppressWarnings("unchecked")
+	public <K, V> Boolean execute(RedisOperations<K, V> operations) throws DataAccessException {
+
+		RedisOperations<String, T> ops = (RedisOperations<String, T>) operations;
+
+		ops.watch(key);
+
+		if (expect.equals(getter.get())) {
+
+			ops.multi();
+			setter.accept(update);
+
+			if (updateSuccessful(operations.exec())) {
+				return true;
+			}
+		}
+
+		ops.unwatch();
+		return false;
+	}
+
+	private static boolean updateSuccessful(Collection<?> exec) {
+		return !CollectionUtils.isEmpty(exec);
+	}
+}

src/main/java/org/springframework/data/redis/support/atomic/RedisAtomicDouble.java

@@ -16,7 +16,6 @@
 package org.springframework.data.redis.support.atomic;
 
 import java.io.Serializable;
-import java.util.Collections;
 import java.util.Date;
 import java.util.concurrent.TimeUnit;
 
@@ -26,11 +25,9 @@ import org.springframework.data.redis.connection.RedisConnectionFactory;
 import org.springframework.data.redis.core.BoundKeyOperations;
 import org.springframework.data.redis.core.RedisOperations;
 import org.springframework.data.redis.core.RedisTemplate;
-import org.springframework.data.redis.core.SessionCallback;
 import org.springframework.data.redis.core.ValueOperations;
 import org.springframework.data.redis.serializer.GenericToStringSerializer;
 import org.springframework.data.redis.serializer.RedisSerializer;
-import org.springframework.data.redis.serializer.StringRedisSerializer;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -190,27 +187,7 @@ public class RedisAtomicDouble extends Number implements Serializable, BoundKeyO
 	 *         expected value.
 	 */
 	public boolean compareAndSet(final double expect, final double update) {
-
-		return generalOps.execute(new SessionCallback<Boolean>() {
-
-			@Override
-			@SuppressWarnings({ "unchecked", "rawtypes" })
-			public Boolean execute(RedisOperations operations) {
-				for (;;) {
-					operations.watch(Collections.singleton(key));
-					if (expect == get()) {
-						generalOps.multi();
-						set(update);
-						if (operations.exec() != null) {
-							return true;
-						}
-					}
-					{
-						return false;
-					}
-				}
-			}
-		});
+		return generalOps.execute(new CompareAndSet<>(this::get, this::set, key, expect, update));
 	}
 
 	/**

src/main/java/org/springframework/data/redis/support/atomic/RedisAtomicInteger.java

@@ -16,7 +16,6 @@
 package org.springframework.data.redis.support.atomic;
 
 import java.io.Serializable;
-import java.util.Collections;
 import java.util.Date;
 import java.util.concurrent.TimeUnit;
 
@@ -26,7 +25,6 @@ import org.springframework.data.redis.connection.RedisConnectionFactory;
 import org.springframework.data.redis.core.BoundKeyOperations;
 import org.springframework.data.redis.core.RedisOperations;
 import org.springframework.data.redis.core.RedisTemplate;
-import org.springframework.data.redis.core.SessionCallback;
 import org.springframework.data.redis.core.ValueOperations;
 import org.springframework.data.redis.serializer.GenericToStringSerializer;
 import org.springframework.data.redis.serializer.RedisSerializer;
@@ -187,27 +185,7 @@ public class RedisAtomicInteger extends Number implements Serializable, BoundKey
 	 *         expected value.
 	 */
 	public boolean compareAndSet(int expect, int update) {
-
-		return generalOps.execute(new SessionCallback<Boolean>() {
-
-			@Override
-			@SuppressWarnings("unchecked")
-			public Boolean execute(RedisOperations operations) {
-				for (;;) {
-					operations.watch(Collections.singleton(key));
-					if (expect == get()) {
-						generalOps.multi();
-						set(update);
-						if (operations.exec() != null) {
-							return true;
-						}
-					}
-					{
-						return false;
-					}
-				}
-			}
-		});
+		return generalOps.execute(new CompareAndSet<>(this::get, this::set, key, expect, update));
 	}
 
 	/**

src/main/java/org/springframework/data/redis/support/atomic/RedisAtomicLong.java

@@ -16,7 +16,6 @@
 package org.springframework.data.redis.support.atomic;
 
 import java.io.Serializable;
-import java.util.Collections;
 import java.util.Date;
 import java.util.concurrent.TimeUnit;
 
@@ -26,7 +25,6 @@ import org.springframework.data.redis.connection.RedisConnectionFactory;
 import org.springframework.data.redis.core.BoundKeyOperations;
 import org.springframework.data.redis.core.RedisOperations;
 import org.springframework.data.redis.core.RedisTemplate;
-import org.springframework.data.redis.core.SessionCallback;
 import org.springframework.data.redis.core.ValueOperations;
 import org.springframework.data.redis.serializer.GenericToStringSerializer;
 import org.springframework.data.redis.serializer.RedisSerializer;
@@ -194,27 +192,7 @@ public class RedisAtomicLong extends Number implements Serializable, BoundKeyOpe
 	 *         expected value.
 	 */
 	public boolean compareAndSet(long expect, long update) {
-
-		return generalOps.execute(new SessionCallback<Boolean>() {
-
-			@Override
-			@SuppressWarnings("unchecked")
-			public Boolean execute(RedisOperations operations) {
-				for (;;) {
-					operations.watch(Collections.singleton(key));
-					if (expect == get()) {
-						generalOps.multi();
-						set(update);
-						if (operations.exec() != null) {
-							return true;
-						}
-					}
-					{
-						return false;
-					}
-				}
-			}
-		});
+		return generalOps.execute(new CompareAndSet<>(this::get, this::set, key, expect, update));
 	}
 
 	/**