Package 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

    • Constructor Details

      • FC

        public FC()

    • Method Details

      • 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