order

This paper mainly studies the reconnectAttempts of artemis

reconnectAttempts

activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ServerLocatorImpl.java

public final class ServerLocatorImpl implements ServerLocatorInternal, DiscoveryListener {

   //......

   public ClientSessionFactory createSessionFactory(final TransportConfiguration transportConfiguration,
                                                    int reconnectAttempts) throws Exception {
      assertOpen();

      initialize();

      ClientSessionFactoryInternal factory = new ClientSessionFactoryImpl(this, transportConfiguration, callTimeout, callFailoverTimeout, clientFailureCheckPeriod, connectionTTL, retryInterval, retryIntervalMultiplier, maxRetryInterval, reconnectAttempts, threadPool, scheduledThreadPool, incomingInterceptors, outgoingInterceptors);

      addToConnecting(factory);
      try {
         try {
            factory.connect(reconnectAttempts);
         } catch (ActiveMQException e1) {
            //we need to make sure is closed just for garbage collection
            factory.close();
            throw e1;
         }
         addFactory(factory);
         return factory;
      } finally {
         removeFromConnecting(factory);
      }
   }

   //......
}

• Create ClientSessionFactoryImpl with the createSessionFactory method of ServerLocatorImpl, and then execute factory.connect(reconnectAttempts)

ClientSessionFactoryImpl

activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ClientSessionFactoryImpl.java

public class ClientSessionFactoryImpl implements ClientSessionFactoryInternal, ClientConnectionLifeCycleListener {

   //......

   public void connect(final int initialConnectAttempts) throws ActiveMQException {
      // Get the connection
      getConnectionWithRetry(initialConnectAttempts, null);

      if (connection == null) {
         StringBuilder msg = new StringBuilder("Unable to connect to server using configuration ").append(currentConnectorConfig);
         if (backupConfig != null) {
            msg.append(" and backup configuration ").append(backupConfig);
         }
         throw new ActiveMQNotConnectedException(msg.toString());
      }

   }

   private void getConnectionWithRetry(final int reconnectAttempts, RemotingConnection oldConnection) {
      if (!clientProtocolManager.isAlive())
         return;
      if (logger.isTraceEnabled()) {
         logger.trace("getConnectionWithRetry::" + reconnectAttempts +
                         " with retryInterval = " +
                         retryInterval +
                         " multiplier = " +
                         retryIntervalMultiplier, new Exception("trace"));
      }

      long interval = retryInterval;

      int count = 0;

      while (clientProtocolManager.isAlive()) {
         if (logger.isDebugEnabled()) {
            logger.debug("Trying reconnection attempt " + count + "/" + reconnectAttempts);
         }

         if (getConnection() != null) {
            if (oldConnection != null && oldConnection instanceof CoreRemotingConnection) {
               // transferring old connection version into the new connection
               ((CoreRemotingConnection)connection).setChannelVersion(((CoreRemotingConnection)oldConnection).getChannelVersion());
            }
            if (logger.isDebugEnabled()) {
               logger.debug("Reconnection successful");
            }
            return;
         } else {
            // Failed to get connection

            if (reconnectAttempts != 0) {
               count++;

               if (reconnectAttempts != -1 && count == reconnectAttempts) {
                  if (reconnectAttempts != 1) {
                     ActiveMQClientLogger.LOGGER.failedToConnectToServer(reconnectAttempts);
                  }

                  return;
               }

               if (ClientSessionFactoryImpl.logger.isTraceEnabled()) {
                  ClientSessionFactoryImpl.logger.trace("Waiting " + interval + " milliseconds before next retry. RetryInterval=" + retryInterval + " and multiplier=" + retryIntervalMultiplier);
               }

               if (waitForRetry(interval))
                  return;

               // Exponential back-off
               long newInterval = (long) (interval * retryIntervalMultiplier);

               if (newInterval > maxRetryInterval) {
                  newInterval = maxRetryInterval;
               }

               interval = newInterval;
            } else {
               logger.debug("Could not connect to any server. Didn't have reconnection configured on the ClientSessionFactory");
               return;
            }
         }
      }
   }

   public boolean waitForRetry(long interval) {
      try {
         if (clientProtocolManager.waitOnLatch(interval)) {
            return true;
         }
      } catch (InterruptedException ignore) {
         throw new ActiveMQInterruptedException(createTrace);
      }
      return false;
   }

   //......
}   

• The connect method of ClientSessionFactoryImpl is mainly to execute getConnectionWithRetry. The getConnectionWithRetry method uses clientProtocolManager.isAlive() condition to execute getconnection in a while loop. If it is null and reconnectAttempts is not 0, it will retry, increasing count. When reconnectAttempts is not - 1 and reconnectAttempts is equal to count, it will jump out of the loop and retry Wait by waitForRetry(interval). If it returns true, return in advance. Otherwise, update the interval for the next cycle. waitForRetry waits by clientProtocolManager.waitOnLatch(interval)

ActiveMQClientProtocolManager

activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/protocol/core/impl/ActiveMQClientProtocolManager.java

public class ActiveMQClientProtocolManager implements ClientProtocolManager {

   //......

   private final CountDownLatch waitLatch = new CountDownLatch(1);

   //......

   public boolean waitOnLatch(long milliseconds) throws InterruptedException {
      return waitLatch.await(milliseconds, TimeUnit.MILLISECONDS);
   }

   public void stop() {
      alive = false;

      synchronized (inCreateSessionGuard) {
         if (inCreateSessionLatch != null)
            inCreateSessionLatch.countDown();
      }

      Channel channel1 = getChannel1();
      if (channel1 != null) {
         channel1.returnBlocking();
      }

      waitLatch.countDown();

   }

   //......
}

• ActiveMQClientProtocolManager has a CountDownLatch named waitLatch. The waitOnLatch method waits through waitLatch.await(milliseconds, TimeUnit.MILLISECONDS), while the stop method executes waitLatch.countDown()

Summary

The connect method of ClientSessionFactoryImpl is mainly to execute getConnectionWithRetry. The getConnectionWithRetry method uses clientProtocolManager.isAlive() condition to execute getconnection in a while loop. If it is null and reconnectAttempts is not 0, it will retry, increasing count. When reconnectAttempts is not - 1 and reconnectAttempts is equal to count, it will jump out of the loop and retry Wait by waitForRetry(interval). If it returns true, return in advance. Otherwise, update the interval for the next cycle. waitForRetry waits by clientProtocolManager.waitOnLatch(interval)

doc

• ClientSessionFactoryImpl