org.javagroups.protocols
Class FLOW_CONTROL

java.lang.Object
  |
  +--org.javagroups.stack.Protocol
        |
        +--org.javagroups.stack.MessageProtocol
              |
              +--org.javagroups.protocols.FLOW_CONTROL
All Implemented Interfaces:
RequestHandler, java.lang.Runnable

public class FLOW_CONTROL
extends MessageProtocol
implements java.lang.Runnable

FLOW_CONTROL provides end-end congestion control and flow control. Attempts to maximize through put, by minimizing the possible block times(Forward flow control). Initially, sender starts with a smaller window size W and large expected RTT grpRTT. Sender also keeps a margin in the window size. When the margin is hit, insted of waiting for the window size to be exhausted, sender multicasts a FLOW_CONTROL info request message. If the window size is exhausted before the responses are received, send will be blocked. FCInfo(flow control info) from all the receivers is gathered at the sender, and current RTT is computed. If the current RTT is greater than estimated RTT window size and margin are reduced, otherwise they are increased.
Horizontal interaction is initiated by the sender with the other group members.
Note: A reliable transport layer is required for this protocol to function properly. With little effort this can be made completely independent.
todo: handle view changes (e.g. members {A,B,C}, blocked on C, and C crashes --> unblock todo: block on down() instead of sending BLOCK_SEND

Author:
Ananda Bollu

Field Summary
 
Fields inherited from class org.javagroups.stack.MessageProtocol
_corr, members
 
Fields inherited from class org.javagroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, observer, props, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
FLOW_CONTROL()
           
 
Method Summary
 java.lang.String getName()
           
 java.lang.Object handle(Message req)
          Called when a request for this protocol layer is received.
 boolean handleDownEvent(Event evt)
          If Event.MSG type is received count is incremented by one, and message is passed to the down_prot.
 boolean handleUpEvent(Event evt)
          If Event.MSG type is received message, number of received messages from the sender is incremented.
 void run()
          FCInfo request must be submitted in a different thread.
 boolean setProperties(java.util.Properties props)
          Following parameters can be optionally supplied: window size cap - int Limits the window size to a reasonable value.
 
Methods inherited from class org.javagroups.stack.MessageProtocol
castMessage, down, sendMessage, start, stop, up, updateView
 
Methods inherited from class org.javagroups.stack.Protocol
destroy, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FLOW_CONTROL

public FLOW_CONTROL()
Method Detail

getName

public java.lang.String getName()
Specified by:
getName in class Protocol

handleDownEvent

public boolean handleDownEvent(Event evt)
If Event.MSG type is received count is incremented by one, and message is passed to the down_prot. At some point, based on the algorithm(FLOW_CONTROL protocol definition) data collection sequence is started. This is done by each member in SENDER role when _numMSGsSentThisPeriod hits the margin. Before rsp arrives only _fwdMarginSize number of messages can be sent, and then sender will be blocked.

Overrides:
handleDownEvent in class MessageProtocol

handleUpEvent

public boolean handleUpEvent(Event evt)
If Event.MSG type is received message, number of received messages from the sender is incremented. And the message is passed up the stack.

Overrides:
handleUpEvent in class MessageProtocol

handle

public java.lang.Object handle(Message req)
Called when a request for this protocol layer is received. Processes and return value is sent back in the reply. FLOW_CONTROL protocol of all members gets this message(including sender?)

Specified by:
handle in interface RequestHandler
Overrides:
handle in class MessageProtocol
Returns:
Object containing FC information for sender with senderID. Callback. Called when a request for this protocol layer is received.

run

public void run()
FCInfo request must be submitted in a different thread. handleDownEvent() can still be called to send messages while waiting for FCInfo from receivers. usually takes RTT.

Specified by:
run in interface java.lang.Runnable

setProperties

public boolean setProperties(java.util.Properties props)
Following parameters can be optionally supplied:

Overrides:
setProperties in class Protocol
See Also:
Protocol.setProperties(Properties)


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