org.jgroups.protocols.pbcast.ClientGmsImpl Maven / Gradle / Ivy
// $Id: ClientGmsImpl.java,v 1.18 2005/04/12 18:59:49 belaban Exp $
package org.jgroups.protocols.pbcast;
import org.jgroups.*;
import org.jgroups.protocols.PingRsp;
import org.jgroups.util.Promise;
import org.jgroups.util.Util;
import java.util.*;
/**
* Client part of GMS. Whenever a new member wants to join a group, it starts in the CLIENT role.
* No multicasts to the group will be received and processed until the member has been joined and
* turned into a SERVER (either coordinator or participant, mostly just participant). This class
* only implements Join (called by clients who want to join a certain group, and
* ViewChange which is called by the coordinator that was contacted by this client, to
* tell the client what its initial membership is.
* @author Bela Ban
* @version $Revision: 1.18 $
*/
public class ClientGmsImpl extends GmsImpl {
private final Vector initial_mbrs=new Vector(11);
private boolean initial_mbrs_received=false;
private final Promise join_promise=new Promise();
public ClientGmsImpl(GMS g) {
gms=g;
}
public void init() throws Exception {
super.init();
synchronized(initial_mbrs) {
initial_mbrs.clear();
initial_mbrs_received=false;
}
join_promise.reset();
}
/**
* Joins this process to a group. Determines the coordinator and sends a unicast
* handleJoin() message to it. The coordinator returns a JoinRsp and then broadcasts the new view, which
* contains a message digest and the current membership (including the joiner). The joiner is then
* supposed to install the new view and the digest and starts accepting mcast messages. Previous
* mcast messages were discarded (this is done in PBCAST).
* If successful, impl is changed to an instance of ParticipantGmsImpl.
* Otherwise, we continue trying to send join() messages to the coordinator,
* until we succeed (or there is no member in the group. In this case, we create our own singleton group).
*
When GMS.disable_initial_coord is set to true, then we won't become coordinator on receiving an initial
* membership of 0, but instead will retry (forever) until we get an initial membership of > 0.
* @param mbr Our own address (assigned through SET_LOCAL_ADDRESS)
*/
public void join(Address mbr) {
Address coord=null;
JoinRsp rsp=null;
Digest tmp_digest=null;
leaving=false;
join_promise.reset();
while(!leaving) {
findInitialMembers();
if(log.isDebugEnabled()) log.debug("initial_mbrs are " + initial_mbrs);
if(initial_mbrs.size() == 0) {
if(gms.disable_initial_coord) {
if(log.isTraceEnabled())
log.trace("received an initial membership of 0, but cannot become coordinator " +
"(disable_initial_coord=true), will retry fetching the initial membership");
continue;
}
if(log.isDebugEnabled())
log.debug("no initial members discovered: creating group as first member");
becomeSingletonMember(mbr);
return;
}
coord=determineCoord(initial_mbrs);
if(coord == null) { // e.g. because we have all clients only
if(log.isTraceEnabled())
log.trace("could not determine coordinator from responses " + initial_mbrs);
// so the member to become singleton member (and thus coord) is the first of all clients
Set clients=new TreeSet(); // sorted
clients.add(mbr); // add myself again (was removed by findInitialMembers())
for(int i=0; i < initial_mbrs.size(); i++) {
PingRsp pingRsp=(PingRsp)initial_mbrs.elementAt(i);
Address client_addr=pingRsp.getAddress();
if(client_addr != null)
clients.add(client_addr);
}
if(log.isTraceEnabled())
log.trace("clients to choose new coord from are: " + clients);
Address new_coord=(Address)clients.iterator().next();
if(new_coord.equals(mbr)) {
if(log.isTraceEnabled())
log.trace("I'm the first of the clients, will become singleton");
becomeSingletonMember(mbr);
return;
}
else {
if(log.isTraceEnabled())
log.trace("I'm not the first of the clients, waiting for another client to become coord");
Util.sleep(500);
}
continue;
}
try {
if(log.isDebugEnabled())
log.debug("sending handleJoin(" + mbr + ") to " + coord);
sendJoinMessage(coord, mbr);
rsp=(JoinRsp)join_promise.getResult(gms.join_timeout);
if(rsp == null) {
if(log.isWarnEnabled()) log.warn("join(" + mbr + ") failed, retrying");
}
else {
// 1. Install digest
tmp_digest=rsp.getDigest();
if(tmp_digest != null) {
tmp_digest.incrementHighSeqno(coord); // see DESIGN for an explanantion
if(log.isDebugEnabled()) log.debug("digest is " + tmp_digest);
gms.setDigest(tmp_digest);
}
else
if(log.isErrorEnabled()) log.error("digest of JOIN response is null");
// 2. Install view
if(log.isDebugEnabled()) log.debug("[" + gms.local_addr + "]: JoinRsp=" + rsp.getView() +
" [size=" + rsp.getView().size() + "]\n\n");
if(rsp.getView() != null) {
if(!installView(rsp.getView())) {
if(log.isErrorEnabled()) log.error("view installation failed, retrying to join group");
continue;
}
gms.passUp(new Event(Event.BECOME_SERVER));
gms.passDown(new Event(Event.BECOME_SERVER));
return;
}
else
if(log.isErrorEnabled()) log.error("view of JOIN response is null");
}
}
catch(Exception e) {
if(log.isDebugEnabled()) log.debug("exception=" + e.toString() + ", retrying");
}
Util.sleep(gms.join_retry_timeout);
}
}
public void leave(Address mbr) {
leaving=true;
wrongMethod("leave");
}
public void handleJoinResponse(JoinRsp join_rsp) {
join_promise.setResult(join_rsp); // will wake up join() method
}
public void handleLeaveResponse() {
; // safely ignore this
}
public void suspect(Address mbr) {
;
}
public void unsuspect(Address mbr) {
wrongMethod("unsuspect");
}
public JoinRsp handleJoin(Address mbr) {
wrongMethod("handleJoin");
return null;
}
/** Returns false. Clients don't handle leave() requests */
public void handleLeave(Address mbr, boolean suspected) {
wrongMethod("handleLeave");
}
/**
* Does nothing. Discards all views while still client.
*/
public synchronized void handleViewChange(View new_view, Digest digest) {
if(log.isDebugEnabled()) log.debug("view " + new_view.getMembers() +
" is discarded as we are not a participant");
}
/**
* Called by join(). Installs the view returned by calling Coord.handleJoin() and
* becomes coordinator.
*/
private boolean installView(View new_view) {
Vector mems=new_view.getMembers();
if(log.isDebugEnabled()) log.debug("new_view=" + new_view);
if(gms.local_addr == null || mems == null || !mems.contains(gms.local_addr)) {
if(log.isErrorEnabled()) log.error("I (" + gms.local_addr +
") am not member of " + mems + ", will not install view");
return false;
}
gms.installView(new_view);
gms.becomeParticipant();
gms.passUp(new Event(Event.BECOME_SERVER));
gms.passDown(new Event(Event.BECOME_SERVER));
return true;
}
/** Returns immediately. Clients don't handle suspect() requests */
public void handleSuspect(Address mbr) {
wrongMethod("handleSuspect");
return;
}
public boolean handleUpEvent(Event evt) {
Vector tmp;
switch(evt.getType()) {
case Event.FIND_INITIAL_MBRS_OK:
tmp=(Vector)evt.getArg();
synchronized(initial_mbrs) {
if(tmp != null && tmp.size() > 0) {
initial_mbrs.addAll(tmp);
}
initial_mbrs_received=true;
initial_mbrs.notifyAll();
}
return false; // don't pass up the stack
}
return true;
}
/* --------------------------- Private Methods ------------------------------------ */
void sendJoinMessage(Address coord, Address mbr) {
Message msg;
GMS.GmsHeader hdr;
msg=new Message(coord, null, null);
hdr=new GMS.GmsHeader(GMS.GmsHeader.JOIN_REQ, mbr);
msg.putHeader(gms.getName(), hdr);
gms.passDown(new Event(Event.MSG, msg));
}
/**
* Pings initial members. Removes self before returning vector of initial members.
* Uses IP multicast or gossiping, depending on parameters.
*/
void findInitialMembers() {
PingRsp ping_rsp;
synchronized(initial_mbrs) {
initial_mbrs.removeAllElements();
initial_mbrs_received=false;
gms.passDown(new Event(Event.FIND_INITIAL_MBRS));
// the initial_mbrs_received flag is needed when passDown() is executed on the same thread, so when
// it returns, a response might actually have been received (even though the initial_mbrs might still be empty)
if(initial_mbrs_received == false) {
try {
initial_mbrs.wait();
}
catch(Exception e) {
}
}
for(int i=0; i < initial_mbrs.size(); i++) {
ping_rsp=(PingRsp)initial_mbrs.elementAt(i);
if(ping_rsp.own_addr != null && gms.local_addr != null &&
ping_rsp.own_addr.equals(gms.local_addr)) {
initial_mbrs.removeElementAt(i);
break;
}
}
}
}
/**
The coordinator is determined by a majority vote. If there are an equal number of votes for
more than 1 candidate, we determine the winner randomly.
*/
Address determineCoord(Vector mbrs) {
PingRsp mbr;
Hashtable votes;
int count, most_votes;
Address winner=null, tmp;
if(mbrs == null || mbrs.size() < 1)
return null;
votes=new Hashtable(5);
// count *all* the votes (unlike the 2000 election)
for(int i=0; i < mbrs.size(); i++) {
mbr=(PingRsp)mbrs.elementAt(i);
if(mbr.is_server && mbr.coord_addr != null) {
if(!votes.containsKey(mbr.coord_addr))
votes.put(mbr.coord_addr, new Integer(1));
else {
count=((Integer)votes.get(mbr.coord_addr)).intValue();
votes.put(mbr.coord_addr, new Integer(count + 1));
}
}
}
if(log.isDebugEnabled()) {
if(votes.size() > 1)
if(log.isWarnEnabled()) log.warn("there was more than 1 candidate for coordinator: " + votes);
else
if(log.isDebugEnabled()) log.debug("election results: " + votes);
}
// determine who got the most votes
most_votes=0;
for(Enumeration e=votes.keys(); e.hasMoreElements();) {
tmp=(Address)e.nextElement();
count=((Integer)votes.get(tmp)).intValue();
if(count > most_votes) {
winner=tmp;
// fixed July 15 2003 (patch submitted by Darren Hobbs, patch-id=771418)
most_votes=count;
}
}
votes.clear();
return winner;
}
void becomeSingletonMember(Address mbr) {
Digest initial_digest;
ViewId view_id=null;
Vector mbrs=new Vector(1);
// set the initial digest (since I'm the first member)
initial_digest=new Digest(1); // 1 member (it's only me)
initial_digest.add(gms.local_addr, 0, 0); // initial seqno mcast by me will be 1 (highest seen +1)
gms.setDigest(initial_digest);
view_id=new ViewId(mbr); // create singleton view with mbr as only member
mbrs.addElement(mbr);
gms.installView(new View(view_id, mbrs));
gms.becomeCoordinator(); // not really necessary - installView() should do it
gms.passUp(new Event(Event.BECOME_SERVER));
gms.passDown(new Event(Event.BECOME_SERVER));
if(log.isDebugEnabled()) log.debug("created group (first member). My view is " + gms.view_id +
", impl is " + gms.getImpl().getClass().getName());
}
}