// $Id: GroupRequest.java,v 1.21.2.2 2006/12/09 22:55:26 belaban Exp $
package org.jgroups.blocks;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.jgroups.Address;
import org.jgroups.Message;
import org.jgroups.Transport;
import org.jgroups.View;
import org.jgroups.util.Command;
import org.jgroups.util.Rsp;
import org.jgroups.util.RspList;
import java.util.*;
/**
* Sends a message to all members of the group and waits for all responses (or timeout). Returns a
* boolean value (success or failure). Results (if any) can be retrieved when done.<p>
* The supported transport to send requests is currently either a RequestCorrelator or a generic
* Transport. One of them has to be given in the constructor. It will then be used to send a
* request. When a message is received by either one, the receiveResponse() of this class has to
* be called (this class does not actively receive requests/responses itself). Also, when a view change
* or suspicion is received, the methods viewChange() or suspect() of this class have to be called.<p>
* When started, an array of responses, correlating to the membership, is created. Each response
* is added to the corresponding field in the array. When all fields have been set, the algorithm
* terminates.
* This algorithm can optionally use a suspicion service (failure detector) to detect (and
* exclude from the membership) fauly members. If no suspicion service is available, timeouts
* can be used instead (see <code>execute()</code>). When done, a list of suspected members
* can be retrieved.<p>
* Because a channel might deliver requests, and responses to <em>different</em> requests, the
* <code>GroupRequest</code> class cannot itself receive and process requests/responses from the
* channel. A mechanism outside this class has to do this; it has to determine what the responses
* are for the message sent by the <code>execute()</code> method and call <code>receiveResponse()</code>
* to do so.<p>
* <b>Requirements</b>: lossless delivery, e.g. acknowledgment-based message confirmation.
* @author Bela Ban
* @version $Revision: 1.21.2.2 $
*/
public class GroupRequest implements RspCollector, Command {
/** return only first response */
public static final int GET_FIRST=1;
/** return all responses */
public static final int GET_ALL=2;
/** return majority (of all non-faulty members) */
public static final int GET_MAJORITY=3;
/** return majority (of all members, may block) */
public static final int GET_ABS_MAJORITY=4;
/** return n responses (may block) */
public static final int GET_N=5;
/** return no response (async call) */
public static final int GET_NONE=6;
private Address caller;
/** Map<Address, Rsp>. Maps requests and responses */
private final Map requests=new HashMap();
/** bounded queue of suspected members */
private final Vector suspects=new Vector();
/** list of members, changed by viewChange() */
private final Collection members=new TreeSet();
/** keep suspects vector bounded */
private final int max_suspects=40;
protected Message request_msg;
protected RequestCorrelator corr; // either use RequestCorrelator or ...
protected Transport transport; // Transport (one of them has to be non-null)
protected int rsp_mode=GET_ALL;
protected boolean done=false;
protected long timeout=0;
protected int expected_mbrs=0;
private static final Log log=LogFactory.getLog(GroupRequest.class);
/** to generate unique request IDs (see getRequestId()) */
private static long last_req_id=1;
private long req_id=-1; // request ID for this request
/**
@param m The message to be sent
@param corr The request correlator to be used. A request correlator sends requests tagged with
a unique ID and notifies the sender when matching responses are received. The
reason <code>GroupRequest</code> uses it instead of a <code>Transport</code> is
that multiple requests/responses might be sent/received concurrently.
@param members The initial membership. This value reflects the membership to which the request
is sent (and from which potential responses are expected). Is reset by reset().
@param rsp_mode How many responses are expected. Can be
<ol>
<li><code>GET_ALL</code>: wait for all responses from non-suspected members.
A suspicion service might warn
us when a member from which a response is outstanding has crashed, so it can
be excluded from the responses. If no suspision service is available, a
timeout can be used (a value of 0 means wait forever). <em>If a timeout of
0 is used, no suspicion service is available and a member from which we
expect a response has crashed, this methods blocks forever !</em>.
<li><code>GET_FIRST</code>: wait for the first available response.
<li><code>GET_MAJORITY</code>: wait for the majority of all responses. The
majority is re-computed when a member is suspected.
<li><code>GET_ABS_MAJORITY</code>: wait for the majority of
<em>all</em> members.
This includes failed members, so it may block if no timeout is specified.
<li><code>GET_N</CODE>: wait for N members.
Return if n is >= membership+suspects.
<li><code>GET_NONE</code>: don't wait for any response. Essentially send an
asynchronous message to the group members.
</ol>
*/
public GroupRequest(Message m, RequestCorrelator corr, Vector members, int rsp_mode) {
request_msg=m;
this.corr=corr;
this.rsp_mode=rsp_mode;
reset(members);
// suspects.removeAllElements(); // bela Aug 23 2002: made suspects bounded
}
/**
@param timeout Time to wait for responses (ms). A value of <= 0 means wait indefinitely
(e.g. if a suspicion service is available; timeouts are not needed).
*/
public GroupRequest(Message m, RequestCorrelator corr, Vector members, int rsp_mode,
long timeout, int expected_mbrs) {
this(m, corr, members, rsp_mode);
if(timeout > 0)
this.timeout=timeout;
this.expected_mbrs=expected_mbrs;
}
public GroupRequest(Message m, Transport transport, Vector members, int rsp_mode) {
request_msg=m;
this.transport=transport;
this.rsp_mode=rsp_mode;
reset(members);
// suspects.removeAllElements(); // bela Aug 23 2002: make suspects bounded
}
/**
* @param timeout Time to wait for responses (ms). A value of <= 0 means wait indefinitely
* (e.g. if a suspicion service is available; timeouts are not needed).
*/
public GroupRequest(Message m, Transport transport, Vector members,
int rsp_mode, long timeout, int expected_mbrs) {
this(m, transport, members, rsp_mode);
if(timeout > 0)
this.timeout=timeout;
this.expected_mbrs=expected_mbrs;
}
public Address getCaller() {
return caller;
}
public void setCaller(Address caller) {
this.caller=caller;
}
public boolean execute() throws Exception {
return execute(false);
}
/**
* Sends the message. Returns when n responses have been received, or a
* timeout has occurred. <em>n</em> can be the first response, all
* responses, or a majority of the responses.
*/
public boolean execute(boolean use_anycasting) throws Exception {
if(corr == null && transport == null) {
if(log.isErrorEnabled()) log.error("both corr and transport are null, cannot send group request");
return false;
}
try {
done=false;
boolean retval=doExecute(use_anycasting, timeout);
if(retval == false && log.isTraceEnabled())
log.trace("call did not execute correctly, request is " + this.toString());
return retval;
}
finally {
done=true;
}
}
/**
* This method sets the <code>membership</code> variable to the value of
* <code>members</code>. It requires that the caller already hold the
* <code>rsp_mutex</code> lock.
* @param mbrs The new list of members
*/
public final void reset(Vector mbrs) {
if(mbrs != null) {
Address mbr;
synchronized(requests) {
requests.clear();
for(int i=0; i < mbrs.size(); i++) {
mbr=(Address)mbrs.elementAt(i);
requests.put(mbr, new Rsp(mbr));
}
}
// maintain local membership
synchronized(this.members) {
this.members.clear();
this.members.addAll(mbrs);
}
}
else {
synchronized(requests) {
Rsp rsp;
for(Iterator it=requests.values().iterator(); it.hasNext();) {
rsp=(Rsp)it.next();
rsp.setReceived(false);
rsp.setValue(null);
}
}
}
}
/* ---------------------- Interface RspCollector -------------------------- */
/**
* <b>Callback</b> (called by RequestCorrelator or Transport).
* Adds a response to the response table. When all responses have been received,
* <code>execute()</code> returns.
*/
public void receiveResponse(Object response_value, Address sender) {
if(done) {
if(log.isWarnEnabled()) log.warn("command is done; cannot add response !");
return;
}
if(suspects != null && suspects.size() > 0 && suspects.contains(sender)) {
if(log.isWarnEnabled()) log.warn("received response from suspected member " + sender + "; discarding");
return;
}
synchronized(requests) {
Rsp rsp=(Rsp)requests.get(sender);
if(rsp != null) {
if(rsp.wasReceived() == false) {
rsp.setValue(response_value);
rsp.setReceived(true);
if(log.isTraceEnabled())
log.trace(new StringBuffer("received response for request ").append(req_id).append(", sender=").
append(sender).append(", val=").append(response_value));
requests.notifyAll(); // wakes up execute()
}
}
}
}
/**
* <b>Callback</b> (called by RequestCorrelator or Transport).
* Report to <code>GroupRequest</code> that a member is reported as faulty (suspected).
* This method would probably be called when getting a suspect message from a failure detector
* (where available). It is used to exclude faulty members from the response list.
*/
public void suspect(Address suspected_member) {
Rsp rsp;
if(suspected_member == null)
return;
addSuspect(suspected_member);
synchronized(requests) {
rsp=(Rsp)requests.get(suspected_member);
if(rsp != null) {
rsp.setSuspected(true);
rsp.setValue(null);
requests.notifyAll();
}
}
}
/**
* Any member of 'membership' that is not in the new view is flagged as
* SUSPECTED. Any member in the new view that is <em>not</em> in the
* membership (ie, the set of responses expected for the current RPC) will
* <em>not</em> be added to it. If we did this we might run into the
* following problem:
* <ul>
* <li>Membership is {A,B}
* <li>A sends a synchronous group RPC (which sleeps for 60 secs in the
* invocation handler)
* <li>C joins while A waits for responses from A and B
* <li>If this would generate a new view {A,B,C} and if this expanded the
* response set to {A,B,C}, A would wait forever on C's response because C
* never received the request in the first place, therefore won't send a
* response.
* </ul>
*/
public void viewChange(View new_view) {
Address mbr;
Vector mbrs=new_view != null? new_view.getMembers() : null;
if(requests == null || requests.size() == 0 || mbrs == null)
return;
synchronized(this.members) {
this.members.clear();
this.members.addAll(mbrs);
}
Map.Entry entry;
Rsp rsp;
boolean modified=false;
synchronized(requests) {
for(Iterator it=requests.entrySet().iterator(); it.hasNext();) {
entry=(Map.Entry)it.next();
mbr=(Address)entry.getKey();
if(!mbrs.contains(mbr)) {
addSuspect(mbr);
rsp=(Rsp)entry.getValue();
rsp.setValue(null);
rsp.setSuspected(true);
modified=true;
}
}
if(modified)
requests.notifyAll();
}
}
/* -------------------- End of Interface RspCollector ----------------------------------- */
/** Returns the results as a RspList */
public RspList getResults() {
synchronized(requests) {
Collection rsps=requests.values();
return new RspList(rsps);
}
}
public String toString() {
StringBuffer ret=new StringBuffer(128);
ret.append("[GroupRequest:\n");
ret.append("req_id=").append(req_id).append('\n');
if(caller != null)
ret.append("caller=").append(caller).append("\n");
Map.Entry entry;
Address mbr;
Rsp rsp;
synchronized(requests) {
for(Iterator it=requests.entrySet().iterator(); it.hasNext();) {
entry=(Map.Entry)it.next();
mbr=(Address)entry.getKey();
rsp=(Rsp)entry.getValue();
ret.append(mbr).append(": ").append(rsp).append("\n");
}
}
if(suspects.size() > 0)
ret.append("\nsuspects: ").append(suspects);
ret.append("\nrequest_msg: ").append(request_msg);
ret.append("\nrsp_mode: ").append(modeToString(rsp_mode));
ret.append("\ndone: ").append(done);
ret.append("\ntimeout: ").append(timeout);
ret.append("\nexpected_mbrs: ").append(expected_mbrs);
ret.append("\n]");
return ret.toString();
}
public int getNumSuspects() {
return suspects.size();
}
public Vector getSuspects() {
return suspects;
}
public boolean isDone() {
return done;
}
/* --------------------------------- Private Methods -------------------------------------*/
private int determineMajority(int i) {
return i < 2? i : (i / 2) + 1;
}
/** Generates a new unique request ID */
private static synchronized long getRequestId() {
long result=System.currentTimeMillis();
if(result <= last_req_id) {
result=last_req_id + 1;
}
last_req_id=result;
return result;
}
/** This method runs with rsp_mutex locked (called by <code>execute()</code>). */
private boolean doExecute(boolean use_anycasting, long timeout) throws Exception {
long start_time=0;
Address suspect;
req_id=getRequestId();
reset(null); // clear 'responses' array
synchronized(requests) {
for(int i=0; i < suspects.size(); i++) { // mark all suspects in 'received' array
suspect=(Address)suspects.elementAt(i);
Rsp rsp=(Rsp)requests.get(suspect);
if(rsp != null) {
rsp.setSuspected(true);
break; // we can break here because we ensure there are no duplicate members
}
}
}
try {
if(log.isTraceEnabled()) log.trace(new StringBuffer("sending request (id=").append(req_id).append(')'));
if(corr != null) {
java.util.List tmp=new Vector(members);
corr.sendRequest(req_id, tmp, request_msg, rsp_mode == GET_NONE? null : this, use_anycasting);
}
else {
if(use_anycasting) {
List tmp=new ArrayList(members);
Message copy;
Address mbr;
for(Iterator it=tmp.iterator(); it.hasNext();) {
mbr=(Address)it.next();
copy=request_msg.copy(true);
copy.setDest(mbr);
transport.send(copy);
}
}
else {
transport.send(request_msg);
}
}
}
catch(Exception ex) {
if(corr != null)
corr.done(req_id);
throw ex;
}
synchronized(requests) {
if(timeout <= 0) {
while(true) { /* Wait for responses: */
adjustMembership(); // may not be necessary, just to make sure...
if(responsesComplete()) {
if(corr != null) {
corr.done(req_id);
}
if(log.isTraceEnabled()) {
log.trace("received all responses: " + toString());
}
return true;
}
try {
requests.wait();
}
catch(Exception e) {
}
}
}
else {
start_time=System.currentTimeMillis();
while(timeout > 0) { /* Wait for responses: */
if(responsesComplete()) {
if(corr != null)
corr.done(req_id);
if(log.isTraceEnabled()) log.trace("received all responses: " + toString());
return true;
}
timeout=timeout - (System.currentTimeMillis() - start_time);
if(timeout > 0) {
try {
requests.wait(timeout);
}
catch(Exception e) {
}
}
}
if(corr != null) {
corr.done(req_id);
}
return false;
}
}
}
private boolean responsesComplete() {
int num_received=0, num_not_received=0, num_suspected=0;
final int num_total=requests.size();
Rsp rsp;
for(Iterator it=requests.values().iterator(); it.hasNext();) {
rsp=(Rsp)it.next();
if(rsp.wasReceived()) {
num_received++;
}
else {
if(rsp.wasSuspected()) {
num_suspected++;
}
else {
num_not_received++;
}
}
}
switch(rsp_mode) {
case GET_FIRST:
if(num_received > 0)
return true;
if(num_suspected >= num_total)
// e.g. 2 members, and both suspected
return true;
break;
case GET_ALL:
return num_received + num_suspected >= num_total;
case GET_MAJORITY:
int majority=determineMajority(num_total);
if(num_received + num_suspected >= majority)
return true;
break;
case GET_ABS_MAJORITY:
majority=determineMajority(num_total);
if(num_received >= majority)
return true;
break;
case GET_N:
if(expected_mbrs >= num_total) {
rsp_mode=GET_ALL;
return responsesComplete();
}
if(num_received >= expected_mbrs) {
return true;
}
if(num_received + num_not_received < expected_mbrs) {
return num_received + num_suspected >= expected_mbrs;
}
return false;
case GET_NONE:
return true;
default :
if(log.isErrorEnabled()) log.error("rsp_mode " + rsp_mode + " unknown !");
break;
}
return false;
}
/**
* Adjusts the 'received' array in the following way:
* <ul>
* <li>if a member P in 'membership' is not in 'members', P's entry in the 'received' array
* will be marked as SUSPECTED
* <li>if P is 'suspected_mbr', then P's entry in the 'received' array will be marked
* as SUSPECTED
* </ul>
* This call requires exclusive access to rsp_mutex (called by getResponses() which has
* a the rsp_mutex locked, so this should not be a problem).
*/
private void adjustMembership() {
if(requests.size() == 0)
return;
Map.Entry entry;
Address mbr;
Rsp rsp;
for(Iterator it=requests.entrySet().iterator(); it.hasNext();) {
entry=(Map.Entry)it.next();
mbr=(Address)entry.getKey();
if((!this.members.contains(mbr)) || suspects.contains(mbr)) {
addSuspect(mbr);
rsp=(Rsp)entry.getValue();
rsp.setValue(null);
rsp.setSuspected(true);
}
}
}
/**
* Adds a member to the 'suspects' list. Removes oldest elements from 'suspects' list
* to keep the list bounded ('max_suspects' number of elements)
*/
private void addSuspect(Address suspected_mbr) {
if(!suspects.contains(suspected_mbr)) {
suspects.addElement(suspected_mbr);
while(suspects.size() >= max_suspects && suspects.size() > 0)
suspects.remove(0); // keeps queue bounded
}
}
private String modeToString(int m) {
switch(m) {
case GET_FIRST: return "GET_FIRST";
case GET_ALL: return "GET_ALL";
case GET_MAJORITY: return "GET_MAJORITY";
case GET_ABS_MAJORITY: return "GET_ABS_MAJORITY";
case GET_N: return "GET_N";
case GET_NONE: return "GET_NONE";
default: return "<unknown> (" + m + ")";
}
}
}