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

    https://github.com/apache/activemq-artemis/pull/1443#discussion_r131532629
  
    --- Diff: 
artemis-commons/src/main/java/org/apache/activemq/artemis/utils/critical/CriticalAnalyzerImpl.java
 ---
    @@ -0,0 +1,182 @@
    +/**
    + * 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.utils.critical;
    +
    +import java.util.ConcurrentModificationException;
    +import java.util.concurrent.CopyOnWriteArrayList;
    +import java.util.concurrent.Semaphore;
    +import java.util.concurrent.TimeUnit;
    +
    +import org.apache.activemq.artemis.utils.collections.ConcurrentHashSet;
    +import org.jboss.logging.Logger;
    +
    +public class CriticalAnalyzerImpl implements CriticalAnalyzer {
    +
    +   private final Logger logger = Logger.getLogger(CriticalAnalyzer.class);
    +
    +   private volatile long timeout;
    +
    +   private volatile long checkTime;
    +
    +   @Override
    +   public void clear() {
    +      actions.clear();
    +      components.clear();
    +   }
    +
    +   private CopyOnWriteArrayList<CriticalAction> actions = new 
CopyOnWriteArrayList<>();
    +
    +   private Thread thread;
    +
    +   private final Semaphore running = new Semaphore(1);
    +
    +   private final ConcurrentHashSet<CriticalComponent> components = new 
ConcurrentHashSet<>();
    +
    +   @Override
    +   public void add(CriticalComponent component) {
    +      components.add(component);
    +   }
    +
    +   @Override
    +   public void remove(CriticalComponent component) {
    +      components.remove(component);
    +   }
    +
    +   @Override
    +   public CriticalAnalyzer setCheckTime(long timeout) {
    +      this.checkTime = timeout;
    +      return this;
    +   }
    +
    +   @Override
    +   public long getCheckTime() {
    +      if (checkTime == 0) {
    +         checkTime = getTimeout() / 2;
    +      }
    +      return checkTime;
    +   }
    +
    +   @Override
    +   public CriticalAnalyzer setTimeout(long timeout) {
    +      this.timeout = timeout;
    +      return this;
    +   }
    +
    +   @Override
    +   public long getTimeout() {
    +      if (timeout == 0) {
    +         timeout = TimeUnit.MINUTES.toMillis(2);
    +      }
    +      return timeout;
    +   }
    +
    +   @Override
    +   public CriticalAnalyzer addAction(CriticalAction action) {
    +      this.actions.add(action);
    +      return this;
    +   }
    +
    +   @Override
    +   public void check() {
    +      boolean retry = true;
    +      while (retry) {
    +         try {
    +            for (CriticalComponent component : components) {
    +
    +               int pathReturned = component.isExpired(timeout);
    +               if (pathReturned >= 0) {
    +                  fireAction(component, pathReturned);
    +                  // no need to keep running if there's already a 
component failed
    +                  return;
    +               }
    +            }
    +            retry = false; // got to the end of the list, no need to retry
    +         } catch (ConcurrentModificationException dontCare) {
    +            // lets retry on the loop
    +         }
    +      }
    +   }
    +
    +   private void fireAction(CriticalComponent component, int path) {
    +      for (CriticalAction action: actions) {
    +         try {
    +            action.run(component, path);
    +         } catch (Throwable e) {
    +            logger.warn(e.getMessage(), e);
    +         }
    +      }
    +   }
    +
    +   @Override
    +   public void start() {
    +
    +      if (!running.tryAcquire()) {
    +         // already running
    +         return;
    +      }
    +
    +      // we are not using any Thread Pool or any Scheduled Executors from 
the ArtemisServer
    +      // as that would defeat the purpose,
    +      // as in any deadlocks the schedulers may be starving for something 
not responding fast enough
    +      thread = new Thread("Artemis Critical Analyzer") {
    +         @Override
    +         public void run() {
    +            try {
    +               while (true) {
    +                  if (running.tryAcquire(getCheckTime(), 
TimeUnit.MILLISECONDS)) {
    +                     running.release();
    +                     // this means that the server has been stopped as we 
could acquire the semaphore... returning now
    +                     break;
    +                  }
    +                  check();
    +               }
    +            } catch (InterruptedException interrupted) {
    +               // i will just leave on that case
    +            }
    +         }
    +      };
    +
    +      thread.setDaemon(true);
    +
    +      thread.start();
    +   }
    +
    +   @Override
    +   public void stop() {
    --- End diff --
    
    this stop here is like we have in many other components.
    
    
    start means, start the thread.
    stop means shutdown the thread.
    
    I'm not sure what you mean?


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