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[GitHub] activemq-artemis pull request #1722: (WIP DO NOT MERGE) ARTEMIS-1545 Support...


Github user franz1981 commented on a diff in the pull request:

    https://github.com/apache/activemq-artemis/pull/1722#discussion_r157483149
  
    --- Diff: artemis-core-client/src/main/java/org/apache/activemq/artemis/core/protocol/core/impl/ResponseCache.java ---
    @@ -0,0 +1,85 @@
    +/*
    + * 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.activemq.artemis.core.protocol.core.impl;
    +
    +import java.util.concurrent.atomic.AtomicInteger;
    +
    +import org.apache.activemq.artemis.api.core.ActiveMQInterruptedException;
    +import org.apache.activemq.artemis.core.protocol.core.Packet;
    +import org.apache.activemq.artemis.core.protocol.core.ResponseHandler;
    +
    +public class ResponseCache {
    +
    +   private final AtomicInteger writerPointer = new AtomicInteger(0);
    +   private final AtomicInteger sequence = new AtomicInteger(0);
    +
    +   private final Packet[] store;
    +   private ResponseHandler responseHandler;
    +
    +   public ResponseCache(int size) {
    +      this.store = new Packet[size];
    +   }
    +
    +   public long add(Packet packet) {
    +      int pointer = writerPointer.getAndUpdate(operand -> {
    --- End diff --
    
    The `IntUnaryOperator` must be side effect free (it seems not due to `sequence.incrementAndGet` or am I wrong?) because it may be retried due to contention: [AtomicInteger::getAndUpdate](https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicInteger.html#getAndUpdate-java.util.function.IntUnaryOperator-).
    If this `ResponseCache` is (or could be turned into) a `single-writer` cache my suggestion is to avoid complex (and expensive) logic here



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