Complete transactional commands on first Exception #719

Transactional commands now complete exceptionally on the first exception they get completed with. This change allows eager completion without requiring an additional Redis response.

Transactional commands expect two responses: QUEUED and the actual response from the EXEC call hence completion is guarded to expect two completions. Previously, exception responses also expected two completions although a command could already fail upon encoding.

src/main/java/com/lambdaworks/redis/protocol/AsyncCommand.java

@@ -125,7 +125,9 @@ protected void completeResult() {
     @Override
     public boolean completeExceptionally(Throwable ex) {
         boolean result = false;
-        if (COUNT_UPDATER.decrementAndGet(this) == 0) {
+
+        int ref = COUNT_UPDATER.get(this);
+        if (ref > 0 && COUNT_UPDATER.compareAndSet(this, ref, 0)) {
             result = doCompleteExceptionally(ex);
         }
         return result;

src/test/java/com/lambdaworks/redis/protocol/TransactionalCommandTest.java

@@ -0,0 +1,42 @@
+/*
+ * 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 com.lambdaworks.redis.protocol;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+import com.lambdaworks.redis.RedisException;
+import com.lambdaworks.redis.codec.StringCodec;
+import com.lambdaworks.redis.output.StatusOutput;
+
+/**
+ * @author Mark Paluch
+ */
+public class TransactionalCommandTest {
+
+    @Test
+    public void shouldCompleteOnException() {
+
+        RedisCommand<String, String, String> inner = new Command<>(CommandType.SET, new StatusOutput<>(StringCodec.UTF8));
+
+        TransactionalCommand<String, String, String> command = new TransactionalCommand<>(new AsyncCommand<>(inner));
+
+        command.completeExceptionally(new RedisException("foo"));
+
+        assertThat(command).isCompletedExceptionally();
+    }
+}