org.jgroups.protocols
Class MFC

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.protocols.FlowControl
          org.jgroups.protocols.MFC

public class MFC
extends FlowControl

Simple flow control protocol based on a credit system. Each sender has a number of credits (bytes to send). When the credits have been exhausted, the sender blocks. Each receiver also keeps track of how many credits it has received from a sender. When credits for a sender fall below a threshold, the receiver sends more credits to the sender. Works for both unicast and multicast messages.

Note that this protocol must be located towards the top of the stack, or all down_threads from JChannel to this protocol must be set to false ! This is in order to block JChannel.send()/JChannel.down().
This is the second simplified implementation of the same model. The algorithm is sketched out in doc/FlowControl.txt
Changes (Brian) April 2006:

1. Receivers now send credits to a sender when more than min_credits have been received (rather than when min_credits are left)
2. Receivers don't send the full credits (max_credits), but rather the actual number of bytes received

   Author:

   Bela Ban

   Nested Class Summary

   Nested classes/interfaces inherited from class org.jgroups.protocols.FlowControl

   FlowControl.Credit

   Field Summary

   protected CreditMap	credits Maintains credits per member
   protected long	last_credit_request Last time a credit request was sent.

   Fields inherited from class org.jgroups.protocols.FlowControl

   CREDIT_REQUEST_HDR, frag_size_received, ignore_synchronous_response, ignore_thread, max_block_time, max_block_times, max_credits, min_credits, min_threshold, num_credit_requests_received, num_credit_requests_sent, num_credit_responses_received, num_credit_responses_sent, received, REPLENISH_HDR, running

   Fields inherited from class org.jgroups.stack.Protocol

   down_prot, ergonomics, id, log, name, stack, stats, up_prot

   Constructor Summary

   MFC()
   

   Method Summary

   int	getNumberOfBlockings()
   long	getTotalTimeBlocked()
   protected void	handleCredit(Address sender, long increase)
   protected java.lang.Object	handleDownMessage(Event evt, Message msg, Address dest, int length)
   protected boolean	handleMulticastMessage() Whether the protocol handles message with dest == null || dest.isMulticastAddress()
   protected void	handleViewChange(java.util.List<Address> mbrs)
   void	init() Called after instance has been created (null constructor) and before protocol is started.
   protected boolean	needToSendCreditRequest()
   java.lang.String	printCredits()
   java.lang.String	printSenderCredits()
   void	stop() This method is called on a Channel.disconnect().
   void	unblock() Allows to unblock a blocked sender from an external program, e.g.

   Methods inherited from class org.jgroups.protocols.FlowControl

   adjustCredit, down, dumpStats, getAverageTimeBlocked, getMaxBlockTime, getMaxBlockTime, getMaxBlockTimes, getMaxCredits, getMinCredits, getMinThreshold, getNumberOfCreditRequestsReceived, getNumberOfCreditRequestsSent, getNumberOfCreditResponsesReceived, getNumberOfCreditResponsesSent, handleConfigEvent, handleCreditRequest, printMap, printReceiverCredits, resetStats, sendCredit, sendCreditRequest, setMaxBlockTime, setMaxBlockTimes, setMaxCredits, setMinCredits, setMinThreshold, start, up

   Methods inherited from class org.jgroups.stack.Protocol

   destroy, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, isErgonomics, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, statsEnabled

   Methods inherited from class java.lang.Object

   clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

   Field Detail

   credits

   protected CreditMap credits

   Maintains credits per member

   last_credit_request

   protected long last_credit_request

   Last time a credit request was sent. Used to prevent credit request storms

   Constructor Detail

   MFC

   public MFC()

   Method Detail

   unblock

   public void unblock()

   Allows to unblock a blocked sender from an external program, e.g. JMX

   Overrides:

   unblock in class FlowControl

   printCredits

   public java.lang.String printCredits()

   Overrides:

   printCredits in class FlowControl

   printSenderCredits

   public java.lang.String printSenderCredits()

   Specified by:

   printSenderCredits in class FlowControl

   getNumberOfBlockings

   public int getNumberOfBlockings()

   Specified by:

   getNumberOfBlockings in class FlowControl

   getTotalTimeBlocked

   public long getTotalTimeBlocked()

   Specified by:

   getTotalTimeBlocked in class FlowControl

   handleMulticastMessage

   protected boolean handleMulticastMessage()

   Description copied from class: FlowControl

   Whether the protocol handles message with dest == null || dest.isMulticastAddress()

   Specified by:

   handleMulticastMessage in class FlowControl

   Returns:

   init

   public void init()
             throws java.lang.Exception

   Description copied from class: Protocol

   Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.

   Overrides:

   init in class FlowControl

   Throws:

   java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

   stop

   public void stop()

   Description copied from class: Protocol

   This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed

   Overrides:

   stop in class FlowControl

   handleDownMessage

   protected java.lang.Object handleDownMessage(Event evt,
                                                Message msg,
                                                Address dest,
                                                int length)

   Specified by:

   handleDownMessage in class FlowControl

   needToSendCreditRequest

   protected boolean needToSendCreditRequest()

   handleCredit

   protected void handleCredit(Address sender,
                               long increase)

   Specified by:

   handleCredit in class FlowControl

   handleViewChange

   protected void handleViewChange(java.util.List<Address> mbrs)

   Overrides:

   handleViewChange in class FlowControl