聊聊artemis的SessionConsumerFlowCreditMessage

序

本文主要研究一下artemis的SessionConsumerFlowCreditMessage

SessionConsumerFlowCreditMessage

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

public class SessionConsumerFlowCreditMessage extends PacketImpl {

   private long consumerID;
   private int credits;

   public SessionConsumerFlowCreditMessage(final long consumerID, final int credits) {
      super(SESS_FLOWTOKEN);
      this.consumerID = consumerID;
      this.credits = credits;
   }

   public SessionConsumerFlowCreditMessage() {
      super(SESS_FLOWTOKEN);
   }

   // Public --------------------------------------------------------

   public long getConsumerID() {
      return consumerID;
   }

   public int getCredits() {
      return credits;
   }

   @Override
   public void encodeRest(final ActiveMQBuffer buffer) {
      buffer.writeLong(consumerID);
      buffer.writeInt(credits);
   }

   @Override
   public void decodeRest(final ActiveMQBuffer buffer) {
      consumerID = buffer.readLong();
      credits = buffer.readInt();
   }

   @Override
   public String toString() {
      return getParentString() + ", consumerID=" + consumerID + ", credits=" + credits + "]";
   }

   @Override
   public int hashCode() {
      final int prime = 31;
      int result = super.hashCode();
      result = prime * result + (int) (consumerID ^ (consumerID >>> 32));
      result = prime * result + credits;
      return result;
   }

   @Override
   public boolean equals(Object obj) {
      if (this == obj)
         return true;
      if (!super.equals(obj))
         return false;
      if (!(obj instanceof SessionConsumerFlowCreditMessage))
         return false;
      SessionConsumerFlowCreditMessage other = (SessionConsumerFlowCreditMessage) obj;
      if (consumerID != other.consumerID)
         return false;
      if (credits != other.credits)
         return false;
      return true;
   }
}

• SessionConsumerFlowCreditMessage继承了PacketImpl，其type为SESS_FLOWTOKEN

ServerSessionPacketHandler

activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/protocol/core/ServerSessionPacketHandler.java

public class ServerSessionPacketHandler implements ChannelHandler {

   //......

   private volatile AtomicInteger availableCredits = new AtomicInteger(0);

   //......

   private void onMessagePacket(final Packet packet) {
      if (logger.isTraceEnabled()) {
         logger.trace("ServerSessionPacketHandler::handlePacket," + packet);
      }
      final byte type = packet.getType();
      switch (type) {
         case SESS_SEND: {
            onSessionSend(packet);
            break;
         }
         case SESS_ACKNOWLEDGE: {
            onSessionAcknowledge(packet);
            break;
         }
         case SESS_PRODUCER_REQUEST_CREDITS: {
            onSessionRequestProducerCredits(packet);
            break;
         }
         case SESS_FLOWTOKEN: {
            onSessionConsumerFlowCredit(packet);
            break;
         }
         default:
            // separating a method for everything else as JIT was faster this way
            slowPacketHandler(packet);
            break;
      }
   }

   private void onSessionConsumerFlowCredit(Packet packet) {
      this.storageManager.setContext(session.getSessionContext());
      try {
         Packet response = null;
         boolean requiresResponse = false;
         try {
            SessionConsumerFlowCreditMessage message = (SessionConsumerFlowCreditMessage) packet;
            session.receiveConsumerCredits(message.getConsumerID(), message.getCredits());
         } catch (ActiveMQIOErrorException e) {
            response = onActiveMQIOErrorExceptionWhileHandlePacket(packet, e, requiresResponse, response, this.session);
         } catch (ActiveMQXAException e) {
            response = onActiveMQXAExceptionWhileHandlePacket(packet, e, requiresResponse, response);
         } catch (ActiveMQQueueMaxConsumerLimitReached e) {
            response = onActiveMQQueueMaxConsumerLimitReachedWhileHandlePacket(packet, e, requiresResponse, response);
         } catch (ActiveMQException e) {
            response = onActiveMQExceptionWhileHandlePacket(packet, e, requiresResponse, response);
         } catch (Throwable t) {
            response = onCatchThrowableWhileHandlePacket(packet, t, requiresResponse, response, this.session);
         }
         sendResponse(packet, response, false, false);
      } finally {
         this.storageManager.clearContext();
      }
   }

   //......
}

• onMessagePacket方法在type为SESS_FLOWTOKEN时执行onSessionConsumerFlowCredit方法；该方法执行的是session.receiveConsumerCredits以及sendResponse方法

ServerSessionImpl

activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/ServerSessionImpl.java

public class ServerSessionImpl implements ServerSession, FailureListener {

   //......

   public void receiveConsumerCredits(final long consumerID, final int credits) throws Exception {
      ServerConsumer consumer = locateConsumer(consumerID);

      if (consumer == null) {
         logger.debug("There is no consumer with id " + consumerID);

         return;
      }

      consumer.receiveCredits(credits);
   }

   //......
}

• receiveConsumerCredits方法执行的是consumer.receiveCredits方法

ServerConsumerImpl

activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/ServerConsumerImpl.java

public class ServerConsumerImpl implements ServerConsumer, ReadyListener {

   //......

   public void receiveCredits(final int credits) {
      if (credits == -1) {
         if (logger.isDebugEnabled()) {
            logger.debug(this + ":: FlowControl::Received disable flow control message");
         }
         // No flow control
         availableCredits = null;

         // There may be messages already in the queue
         promptDelivery();
      } else if (credits == 0) {
         // reset, used on slow consumers
         logger.debug(this + ":: FlowControl::Received reset flow control message");
         availableCredits.set(0);
      } else {
         int previous = availableCredits.getAndAdd(credits);

         if (logger.isDebugEnabled()) {
            logger.debug(this + "::FlowControl::Received " +
                            credits +
                            " credits, previous value = " +
                            previous +
                            " currentValue = " +
                            availableCredits.get());
         }

         if (previous <= 0 && previous + credits > 0) {
            if (logger.isTraceEnabled()) {
               logger.trace(this + "::calling promptDelivery from receiving credits");
            }
            promptDelivery();
         }
      }
   }

   public void promptDelivery() {
      // largeMessageDeliverer is always set inside a lock
      // if we don't acquire a lock, we will have NPE eventually
      if (largeMessageDeliverer != null) {
         resumeLargeMessage();
      } else {
         forceDelivery();
      }
   }

   private void forceDelivery() {
      if (browseOnly) {
         messageQueue.getExecutor().execute(browserDeliverer);
      } else {
         messageQueue.deliverAsync();
      }
   }

   //......
}

• receiveCredits方法在credits为-1时设置availableCredits为null，然后执行promptDelivery方法；在credits为0时设置availableCredits为0；其他情况执行availableCredits.getAndAdd(credits)；promptDelivery方法主要是执行resumeLargeMessage或者forceDelivery方法

小结

SessionConsumerFlowCreditMessage继承了PacketImpl，其type为SESS_FLOWTOKEN；ServerSessionPacketHandler的onMessagePacket方法在type为SESS_FLOWTOKEN时执行onSessionConsumerFlowCredit方法；该方法执行的是session.receiveConsumerCredits以及sendResponse方法；receiveConsumerCredits方法在receiveCredits方法在credits为-1时设置availableCredits为null，然后执行promptDelivery方法；在credits为0时设置availableCredits为0；其他情况执行availableCredits.getAndAdd(credits)

doc

• SessionConsumerFlowCreditMessage

来源：oschina

链接：https://my.oschina.net/go4it/blog/3159313