frag2.java

来自「JGRoups源码」· Java 代码 · 共 597 行 · 第 1/2 页

package org.jgroups.protocols;

import org.jgroups.Address;
import org.jgroups.Event;
import org.jgroups.Message;
import org.jgroups.View;
import org.jgroups.stack.Protocol;
import org.jgroups.util.Range;
import org.jgroups.util.Util;

import java.util.*;


/**
 * Fragmentation layer. Fragments messages larger than frag_size into smaller packets.
 * Reassembles fragmented packets into bigger ones. The fragmentation number is prepended
 * to the messages as a header (and removed at the receiving side).<p>
 * Each fragment is identified by (a) the sender (part of the message to which the header is appended),
 * (b) the fragmentation ID (which is unique per FRAG2 layer (monotonically increasing) and (c) the
 * fragement ID which ranges from 0 to number_of_fragments-1.<p>
 * Requirement: lossless delivery (e.g. NAK, ACK). No requirement on ordering. Works for both unicast and
 * multicast messages.<br/>
 * Compared to FRAG, this protocol does <em>not</em> need to serialize the message in order to break it into
 * smaller fragments: it looks only at the message's buffer, which is a byte[] array anyway. We assume that the
 * size addition for headers and src and dest address is minimal when the transport finally has to serialize the
 * message, so we add a constant (200 bytes).
 * @author Bela Ban
 * @version $Id: FRAG2.java,v 1.25 2006/08/23 07:20:12 belaban Exp $
 */
public class FRAG2 extends Protocol {

    /** The max number of bytes in a message. If a message's buffer is bigger, it will be fragmented */
    int frag_size=1500;

    /** Number of bytes that we think the headers plus src and dest will take up when
        message is serialized by transport. This will be subtracted from frag_size */
    int overhead=200;

    /*the fragmentation list contains a fragmentation table per sender
     *this way it becomes easier to clean up if a sender (member) leaves or crashes
     */
    private final FragmentationList    fragment_list=new FragmentationList();
    private int                        curr_id=1;
    private final Vector               members=new Vector(11);
    private static final String        name="FRAG2";

    long num_sent_msgs=0;
    long num_sent_frags=0;
    long num_received_msgs=0;
    long num_received_frags=0;


    public final String getName() {
        return name;
    }

    public int getFragSize() {return frag_size;}
    public void setFragSize(int s) {frag_size=s;}
    public int getOverhead() {return overhead;}
    public void setOverhead(int o) {overhead=o;}
    public long getNumberOfSentMessages() {return num_sent_msgs;}
    public long getNumberOfSentFragments() {return num_sent_frags;}
    public long getNumberOfReceivedMessages() {return num_received_msgs;}
    public long getNumberOfReceivedFragments() {return num_received_frags;}


    synchronized int getNextId() {
        return curr_id++;
    }

    /** Setup the Protocol instance acording to the configuration string */
    public boolean setProperties(Properties props) {
        String str;

        super.setProperties(props);
        str=props.getProperty("frag_size");
        if(str != null) {
            frag_size=Integer.parseInt(str);
            props.remove("frag_size");
        }

        str=props.getProperty("overhead");
        if(str != null) {
            overhead=Integer.parseInt(str);
            props.remove("overhead");
        }

        int old_frag_size=frag_size;
        frag_size-=overhead;
        if(frag_size <=0) {
            log.error("frag_size=" + old_frag_size + ", overhead=" + overhead +
                      ", new frag_size=" + frag_size + ": new frag_size is invalid");
            return false;
        }

        if(log.isInfoEnabled())
            log.info("frag_size=" + old_frag_size + ", overhead=" + overhead + ", new frag_size=" + frag_size);

        if(props.size() > 0) {
            log.error("FRAG2.setProperties(): the following properties are not recognized: " + props);
            return false;
        }
        return true;
    }


    public void resetStats() {
        super.resetStats();
        num_sent_msgs=num_sent_frags=num_received_msgs=num_received_frags=0;
    }



    /**
     * Fragment a packet if larger than frag_size (add a header). Otherwise just pass down. Only
     * add a header if framentation is needed !
     */
    public void down(Event evt) {
        switch(evt.getType()) {

        case Event.MSG:
            Message msg=(Message)evt.getArg();
            long size=msg.getLength();
            synchronized(this) {
                num_sent_msgs++;
            }
            if(size > frag_size) {
                if(trace) {
                    StringBuffer sb=new StringBuffer("message's buffer size is ");
                    sb.append(size).append(", will fragment ").append("(frag_size=");
                    sb.append(frag_size).append(')');
                    log.trace(sb.toString());
                }
                fragment(msg);  // Fragment and pass down
                return;
            }
            break;

        case Event.VIEW_CHANGE:
            //don't do anything if this dude is sending out the view change
            //we are receiving a view change,
            //in here we check for the
            View view=(View)evt.getArg();
            Vector new_mbrs=view.getMembers(), left_mbrs;
            Address mbr;

            left_mbrs=Util.determineLeftMembers(members, new_mbrs);
            members.clear();
            members.addAll(new_mbrs);

            for(int i=0; i < left_mbrs.size(); i++) {
                mbr=(Address)left_mbrs.elementAt(i);
                //the new view doesn't contain the sender, he must have left,
                //hence we will clear all his fragmentation tables
                fragment_list.remove(mbr);
                if(trace) log.trace("[VIEW_CHANGE] removed " + mbr + " from fragmentation table");
            }
            break;

        case Event.CONFIG:
            passDown(evt);
            if(log.isDebugEnabled()) log.debug("received CONFIG event: " + evt.getArg());
            handleConfigEvent((HashMap)evt.getArg());
            return;
        }

        passDown(evt);  // Pass on to the layer below us
    }


    /**
     * If event is a message, if it is fragmented, re-assemble fragments into big message and pass up
     * the stack.
     */
    public void up(Event evt) {
        switch(evt.getType()) {

        case Event.MSG:
            Message msg=(Message)evt.getArg();
            Object obj=msg.getHeader(name);
            if(obj != null && obj instanceof FragHeader) { // needs to be defragmented
                unfragment(msg); // Unfragment and possibly pass up
                return;
            }
            else {
                num_received_msgs++;
            }
            break;

        case Event.CONFIG:
            passUp(evt);
            if(log.isInfoEnabled()) log.info("received CONFIG event: " + evt.getArg());
            handleConfigEvent((HashMap)evt.getArg());
            return;
        }

        passUp(evt); // Pass up to the layer above us by default
    }


    /** Send all fragments as separate messages (with same ID !).
     Example:
     <pre>
     Given the generated ID is 2344, number of fragments=3, message {dst,src,buf}
     would be fragmented into:

     [2344,3,0]{dst,src,buf1},
     [2344,3,1]{dst,src,buf2} and
     [2344,3,2]{dst,src,buf3}
     </pre>
     */
    void fragment(Message msg) {
        byte[]             buffer;
        List               fragments;
        Event              evt;
        FragHeader         hdr;
        Message            frag_msg;
        Address            dest=msg.getDest();
        long               id=getNextId(); // used as seqnos
        int                num_frags;
        StringBuffer       sb;
        Range              r;

        try {
            buffer=msg.getBuffer();
            fragments=Util.computeFragOffsets(buffer, frag_size);
            num_frags=fragments.size();
            synchronized(this) {
                num_sent_frags+=num_frags;
            }

            if(trace) {
                sb=new StringBuffer("fragmenting packet to ");
                sb.append((dest != null ? dest.toString() : "<all members>")).append(" (size=").append(buffer.length);
                sb.append(") into ").append(num_frags).append(" fragment(s) [frag_size=").append(frag_size).append(']');
                log.trace(sb.toString());
            }

            for(int i=0; i < fragments.size(); i++) {
                r=(Range)fragments.get(i);
                // Copy the original msg (needed because we need to copy the headers too)
                frag_msg=msg.copy(false); // don't copy the buffer, only src, dest and headers
                frag_msg.setBuffer(buffer, (int)r.low, (int)r.high);
                hdr=new FragHeader(id, i, num_frags);
                frag_msg.putHeader(name, hdr);
                evt=new Event(Event.MSG, frag_msg);
                passDown(evt);
            }
        }
        catch(Exception e) {
            if(log.isErrorEnabled()) log.error("fragmentation failure", e);
        }
    }


    /**
     1. Get all the fragment buffers
     2. When all are received -> Assemble them into one big buffer
     3. Read headers and byte buffer from big buffer
     4. Set headers and buffer in msg
     5. Pass msg up the stack
     */
    void unfragment(Message msg) {
        FragmentationTable frag_table;
        Address            sender=msg.getSrc();
        Message            assembled_msg;
        FragHeader         hdr=(FragHeader)msg.removeHeader(name);

        frag_table=fragment_list.get(sender);
        if(frag_table == null) {
            frag_table=new FragmentationTable(sender);
            try {
                fragment_list.add(sender, frag_table);
            }
            catch(IllegalArgumentException x) { // the entry has already been added, probably in parallel from another thread
                frag_table=fragment_list.get(sender);
            }
        }
        num_received_frags++;
        assembled_msg=frag_table.add(hdr.id, hdr.frag_id, hdr.num_frags, msg);
        if(assembled_msg != null) {
            try {
                if(trace) log.trace("assembled_msg is " + assembled_msg);
                assembled_msg.setSrc(sender); // needed ? YES, because fragments have a null src !!
                num_received_msgs++;
                passUp(new Event(Event.MSG, assembled_msg));
            }
            catch(Exception e) {
                if(log.isErrorEnabled()) log.error("unfragmentation failed", e);
            }
        }
    }


    void handleConfigEvent(HashMap map) {
        if(map == null) return;
        if(map.containsKey("frag_size")) {
            frag_size=((Integer)map.get("frag_size")).intValue();
            if(log.isDebugEnabled()) log.debug("setting frag_size=" + frag_size);