org.jgroups.protocols
Class FLOW_CONTROL
- Runnable, RequestHandler
public class FLOW_CONTROL
implements 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
down_handler , down_prot , down_queue , down_thread , down_thread_prio , log , observer , props , stack , up_handler , up_prot , up_queue , up_thread , up_thread_prio |
String | getName()
|
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.
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boolean | handleUpEvent(Event evt) - If Event.MSG type is received message, number of received
messages from the sender is incremented.
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void | run() - FCInfo request must be submitted in a different thread.
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boolean | setProperties(Properties props) - Following parameters can be optionally supplied:
- window size cap -
int Limits the window size to a reasonable value.
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destroy , down , getDownProtocol , getDownQueue , getName , getProperties , getUpProtocol , getUpQueue , handleSpecialDownEvent , init , passDown , passUp , providedDownServices , providedUpServices , receiveDownEvent , receiveUpEvent , requiredDownServices , requiredUpServices , setDownProtocol , setObserver , setProperties , setPropertiesInternal , setProtocolStack , setUpProtocol , start , startDownHandler , startUpHandler , stop , stopInternal , up |
FLOW_CONTROL
public FLOW_CONTROL()
handle
public 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?)
- handle in interface RequestHandler
- handle in interface MessageProtocol
- Object containing FC information for sender with senderID.
Callback. Called when a request for this protocol layer is received.
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.
- handleDownEvent in interface 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.
- handleUpEvent in interface MessageProtocol
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.
setProperties
public boolean setProperties(Properties props)
Following parameters can be optionally supplied:
- window size cap -
int
Limits the window size to a reasonable value.
- window size -
int
these many number of messages are sent before a block could happen
- forward margin -
int
a request for flow control information is sent when remaining window size hits this margin
- RTT weight -
double
Max RTT in the group is calculated during each Flow control request. lower number assigns
higher weight to current RTT in estimating RTT.
- window size reduction factor -
double
When current RTT is greater than estimated RTT current window size
is reduced by this multiple.
- window size expansion factor -
double
When current RTT is less than estimated RTT window is incremented
by this multiple.
- setProperties in interface Protocol
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