聊聊artemis的handleConnectionFailure

public class ClientSessionFactoryImpl implements ClientSessionFactoryInternal, ClientConnectionLifeCycleListener {

   //......

   private void handleConnectionFailure(final Object connectionID,
                                        final ActiveMQException me,
                                        String scaleDownTargetNodeID) {
      try {
         failoverOrReconnect(connectionID, me, scaleDownTargetNodeID);
      } catch (ActiveMQInterruptedException e1) {
         // this is just a debug, since an interrupt is an expected event (in case of a shutdown)
         logger.debug(e1.getMessage(), e1);
      } catch (Throwable t) {
         ActiveMQClientLogger.LOGGER.unableToHandleConnectionFailure(t);
         //for anything else just close so clients are un blocked
         close();
         throw t;
      }
   }

   private void failoverOrReconnect(final Object connectionID,
                                    final ActiveMQException me,
                                    String scaleDownTargetNodeID) {
      ActiveMQClientLogger.LOGGER.failoverOrReconnect(connectionID, me);

      for (ClientSessionInternal session : sessions) {
         SessionContext context = session.getSessionContext();
         if (context instanceof ActiveMQSessionContext) {
            ActiveMQSessionContext sessionContext = (ActiveMQSessionContext) context;
            if (sessionContext.isKilled()) {
               setReconnectAttempts(0);
            }
         }
      }

      Set<ClientSessionInternal> sessionsToClose = null;
      if (!clientProtocolManager.isAlive())
         return;
      Lock localFailoverLock = lockFailover();
      try {
         if (connection == null || !connection.getID().equals(connectionID) || !clientProtocolManager.isAlive()) {
            // We already failed over/reconnected - probably the first failure came in, all the connections were failed
            // over then an async connection exception or disconnect
            // came in for one of the already exitLoop connections, so we return true - we don't want to call the
            // listeners again

            return;
         }

         if (ClientSessionFactoryImpl.logger.isTraceEnabled()) {
            logger.trace("Client Connection failed, calling failure listeners and trying to reconnect, reconnectAttempts=" + reconnectAttempts);
         }

         callFailoverListeners(FailoverEventType.FAILURE_DETECTED);
         // We call before reconnection occurs to give the user a chance to do cleanup, like cancel messages
         callSessionFailureListeners(me, false, false, scaleDownTargetNodeID);

         // Now get locks on all channel 1s, whilst holding the failoverLock - this makes sure
         // There are either no threads executing in createSession, or one is blocking on a createSession
         // result.

         // Then interrupt the channel 1 that is blocking (could just interrupt them all)

         // Then release all channel 1 locks - this allows the createSession to exit the monitor

         // Then get all channel 1 locks again - this ensures the any createSession thread has executed the section and
         // returned all its connections to the connection manager (the code to return connections to connection manager
         // must be inside the lock

         // Then perform failover

         // Then release failoverLock

         // The other side of the bargain - during createSession:
         // The calling thread must get the failoverLock and get its' connections when this is
         // locked.
         // While this is still locked it must then get the channel1 lock
         // It can then release the failoverLock
         // It should catch ActiveMQException.INTERRUPTED in the call to channel.sendBlocking
         // It should then return its connections, with channel 1 lock still held
         // It can then release the channel 1 lock, and retry (which will cause locking on
         // failoverLock
         // until failover is complete

         if (reconnectAttempts != 0) {

            if (clientProtocolManager.cleanupBeforeFailover(me)) {

               // Now we absolutely know that no threads are executing in or blocked in
               // createSession,
               // and no
               // more will execute it until failover is complete

               // So.. do failover / reconnection

               RemotingConnection oldConnection = connection;

               connection = null;

               Connector localConnector = connector;
               if (localConnector != null) {
                  try {
                     localConnector.close();
                  } catch (Exception ignore) {
                     // no-op
                  }
               }

               cancelScheduledTasks();

               connector = null;

               reconnectSessions(oldConnection, reconnectAttempts, me);

               if (oldConnection != null) {
                  oldConnection.destroy();
               }

               if (connection != null) {
                  callFailoverListeners(FailoverEventType.FAILOVER_COMPLETED);
               }
            }
         } else {
            RemotingConnection connectionToDestory = connection;
            if (connectionToDestory != null) {
               connectionToDestory.destroy();
            }
            connection = null;
         }

         if (connection == null) {
            synchronized (sessions) {
               sessionsToClose = new HashSet<>(sessions);
            }
            callFailoverListeners(FailoverEventType.FAILOVER_FAILED);
            callSessionFailureListeners(me, true, false, scaleDownTargetNodeID);
         }
      } finally {
         localFailoverLock.unlock();
      }

      // This needs to be outside the failover lock to prevent deadlock
      if (connection != null) {
         callSessionFailureListeners(me, true, true);
      }
      if (sessionsToClose != null) {
         // If connection is null it means we didn't succeed in failing over or reconnecting
         // so we close all the sessions, so they will throw exceptions when attempted to be used

         for (ClientSessionInternal session : sessionsToClose) {
            try {
               session.cleanUp(true);
            } catch (Exception cause) {
               ActiveMQClientLogger.LOGGER.failedToCleanupSession(cause);
            }
         }
      }
   }

   //......
}

public class ClientSessionFactoryImpl implements ClientSessionFactoryInternal, ClientConnectionLifeCycleListener {

   //......

   private void reconnectSessions(final RemotingConnection oldConnection,
                                  final int reconnectAttempts,
                                  final ActiveMQException cause) {
      HashSet<ClientSessionInternal> sessionsToFailover;
      synchronized (sessions) {
         sessionsToFailover = new HashSet<>(sessions);
      }

      for (ClientSessionInternal session : sessionsToFailover) {
         session.preHandleFailover(connection);
      }

      getConnectionWithRetry(reconnectAttempts, oldConnection);

      if (connection == null) {
         if (!clientProtocolManager.isAlive())
            ActiveMQClientLogger.LOGGER.failedToConnectToServer();

         return;
      }

      List<FailureListener> oldListeners = oldConnection.getFailureListeners();

      List<FailureListener> newListeners = new ArrayList<>(connection.getFailureListeners());

      for (FailureListener listener : oldListeners) {
         // Add all apart from the old DelegatingFailureListener
         if (listener instanceof DelegatingFailureListener == false) {
            newListeners.add(listener);
         }
      }

      connection.setFailureListeners(newListeners);

      // This used to be done inside failover
      // it needs to be done on the protocol
      ((CoreRemotingConnection) connection).syncIDGeneratorSequence(((CoreRemotingConnection) oldConnection).getIDGeneratorSequence());

      for (ClientSessionInternal session : sessionsToFailover) {
         if (!session.handleFailover(connection, cause)) {
            connection.destroy();
            this.connection = null;
            return;
         }
      }
   }

   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 RemotingConnection getConnection() {
      if (closed)
         throw new IllegalStateException("ClientSessionFactory is closed!");
      if (!clientProtocolManager.isAlive())
         return null;
      synchronized (connectionLock) {
         if (connection != null) {
            // a connection already exists, so returning the same one
            return connection;
         } else {
            RemotingConnection connection = establishNewConnection();

            this.connection = connection;

            //we check if we can actually connect.
            // we do it here as to receive the reply connection has to be not null
            //make sure to reset this.connection == null
            if (connection != null && liveNodeID != null) {
               try {
                  if (!clientProtocolManager.checkForFailover(liveNodeID)) {
                     connection.destroy();
                     this.connection = null;
                     return null;
                  }
               } catch (ActiveMQException e) {
                  connection.destroy();
                  this.connection = null;
                  return null;
               }
            }

            if (connection != null && serverLocator.getAfterConnectInternalListener() != null) {
               serverLocator.getAfterConnectInternalListener().onConnection(this);
            }

            if (serverLocator.getTopology() != null) {
               if (connection != null) {
                  if (ClientSessionFactoryImpl.logger.isTraceEnabled()) {
                     logger.trace(this + "::Subscribing Topology");
                  }
                  clientProtocolManager.sendSubscribeTopology(serverLocator.isClusterConnection());
               }
            } else {
               logger.debug("serverLocator@" + System.identityHashCode(serverLocator + " had no topology"));
            }

            return connection;
         }
      }
   }

   //......
}