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

Fields

Modifier and Type	Field and Description
protected CreditMap	credits Maintains credits per member
protected long	last_credit_request Last time a credit request was sent.
protected static FcHeader	MFC_CREDIT_REQUEST_HDR
protected static FcHeader	MFC_REPLENISH_HDR

Fields inherited from class org.jgroups.protocols.FlowControl

frag_size, ignore_synchronous_response, local_addr, 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, running

Fields inherited from class org.jgroups.stack.Protocol

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

Constructor Summary

Constructors

Constructor and Description
MFC()

Method Summary

Modifier and Type	Method and Description
double	getAverageTimeBlocked()
protected Header	getCreditRequestHeader()
int	getNumberOfBlockings()
protected Header	getReplenishHeader()
protected void	handleCredit(Address sender, long increase)
protected 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(List<Address> mbrs)
void	init() Called after instance has been created (null constructor) and before protocol is started.
protected boolean	needToSendCreditRequest()
String	printCredits()
String	printSenderCredits()
void	resetStats()
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, bufferToLong, down, dumpStats, getMaxBlockTime, getMaxBlockTime, getMaxBlockTimes, getMaxCredits, getMinCredits, getMinThreshold, getNumberOfCreditRequestsReceived, getNumberOfCreditRequestsSent, getNumberOfCreditResponsesReceived, getNumberOfCreditResponsesSent, handleConfigEvent, handleCreditRequest, handleUpEvent, longToBuffer, printMap, printReceiverCredits, sendCredit, sendCreditRequest, setMaxBlockTime, setMaxBlockTimes, setMaxCredits, setMinCredits, setMinThreshold, start, up, up

Methods inherited from class org.jgroups.stack.Protocol

accept, afterCreationHook, destroy, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getLog, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, isErgonomics, level, parse, 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

MFC_REPLENISH_HDR

protected static final FcHeader MFC_REPLENISH_HDR

MFC_CREDIT_REQUEST_HDR

protected static final FcHeader MFC_CREDIT_REQUEST_HDR

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 String printCredits()

Overrides:

printCredits in class FlowControl

printSenderCredits

public String printSenderCredits()

Specified by:

printSenderCredits in class FlowControl

getNumberOfBlockings

public int getNumberOfBlockings()

Specified by:

getNumberOfBlockings in class FlowControl

getAverageTimeBlocked

public double getAverageTimeBlocked()

Specified by:

getAverageTimeBlocked 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:

getReplenishHeader

protected Header getReplenishHeader()

Specified by:

getReplenishHeader in class FlowControl

getCreditRequestHeader

protected Header getCreditRequestHeader()

Specified by:

getCreditRequestHeader in class FlowControl

init

public void init()
          throws 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:

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

resetStats

public void resetStats()

Overrides:

resetStats in class FlowControl

handleDownMessage

protected 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(List<Address> mbrs)

Overrides:

handleViewChange in class FlowControl