org.jgroups.protocols

Class FC

java.lang.Object

org.jgroups.stack.Protocol

org.jgroups.protocols.FC

public class FC
extends Protocol

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 tha actual number of bytes received

Author:

Bela Ban

Field Summary

Fields inherited from class org.jgroups.stack.Protocol

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

Constructor Summary

Constructors

Constructor and Description
FC()

Method Summary

Methods

Modifier and Type	Method and Description
Object	down(Event evt) An event is to be sent down the stack.
Map<String,Object>	dumpStats()
double	getAverageTimeBlocked()
long	getMaxBlockTime()
String	getMaxBlockTimes()
long	getMaxCredits()
long	getMinCredits()
double	getMinThreshold()
int	getNumberOfBlockings()
int	getNumberOfCreditRequestsReceived()
int	getNumberOfCreditRequestsSent()
int	getNumberOfCreditResponsesReceived()
int	getNumberOfCreditResponsesSent()
long	getTotalTimeBlocked()
void	init() Called after instance has been created (null constructor) and before protocol is started.
String	printCreditors()
String	printCredits()
String	printReceiverCredits()
String	printSenderCredits()
void	resetStats()
void	setMaxBlockTime(long t)
void	setMaxBlockTimes(String str)
void	setMaxCredits(long max_credits)
void	setMinCredits(long min_credits)
void	setMinThreshold(double min_threshold)
String	showLastBlockingTimes()
void	start() This method is called on a Channel.connect(String).
void	stop() This method is called on a Channel.disconnect().
void	unblock() Allows to unblock a blocked sender from an external program, e.g.
Object	up(Event evt) An event was received from the layer below.

Methods inherited from class org.jgroups.stack.Protocol

destroy, enableStats, getConfigurableObjects, getDownProtocol, getId, getLevel, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, 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

Constructor Detail

FC

public FC()

Method Detail

resetStats

public void resetStats()

Overrides:

resetStats in class Protocol

getMaxCredits

public long getMaxCredits()

setMaxCredits

public void setMaxCredits(long max_credits)

getMinThreshold

public double getMinThreshold()

setMinThreshold

public void setMinThreshold(double min_threshold)

getMinCredits

public long getMinCredits()

setMinCredits

public void setMinCredits(long min_credits)

getNumberOfBlockings

public int getNumberOfBlockings()

getMaxBlockTime

public long getMaxBlockTime()

setMaxBlockTime

public void setMaxBlockTime(long t)

setMaxBlockTimes

public void setMaxBlockTimes(String str)

getMaxBlockTimes

public String getMaxBlockTimes()

getTotalTimeBlocked

public long getTotalTimeBlocked()

getAverageTimeBlocked

public double getAverageTimeBlocked()

getNumberOfCreditRequestsReceived

public int getNumberOfCreditRequestsReceived()

getNumberOfCreditRequestsSent

public int getNumberOfCreditRequestsSent()

getNumberOfCreditResponsesReceived

public int getNumberOfCreditResponsesReceived()

getNumberOfCreditResponsesSent

public int getNumberOfCreditResponsesSent()

printSenderCredits

public String printSenderCredits()

printReceiverCredits

public String printReceiverCredits()

printCredits

public String printCredits()

printCreditors

public String printCreditors()

dumpStats

public Map<String,Object> dumpStats()

Overrides:

dumpStats in class Protocol

showLastBlockingTimes

public String showLastBlockingTimes()

unblock

public void unblock()

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

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 Protocol

Throws:

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

start

public void start()
           throws Exception

Description copied from class: Protocol

This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.

Overrides:

start in class Protocol

Throws:

Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) 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 Protocol

down

public Object down(Event evt)

Description copied from class: Protocol

An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using down_prot.down(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using up_prot.up().

Overrides:

down in class Protocol

up

public Object up(Event evt)

Description copied from class: Protocol

An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using down_prot.down() or c) the event (or another event) is sent up the stack using up_prot.up().

Overrides:

up in class Protocol