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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.documentapi.messagebus.protocol;
import com.yahoo.jrt.slobrok.api.Mirror;
import com.yahoo.messagebus.EmptyReply;
import com.yahoo.messagebus.Error;
import com.yahoo.messagebus.ErrorCode;
import com.yahoo.messagebus.Reply;
import com.yahoo.messagebus.routing.Hop;
import com.yahoo.messagebus.routing.Route;
import com.yahoo.messagebus.routing.RoutingContext;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* This policy implements round-robin selection of the configured recipients that are currently registered in slobrok.
*
* @author Simon Thoresen Hult
*/
public class RoundRobinPolicy implements DocumentProtocolRoutingPolicy {
private final Map<String, CacheEntry> cache = new HashMap<>();
// Inherit doc from RoutingPolicy.
public void select(RoutingContext ctx) {
Hop hop = getRecipient(ctx);
if (hop != null) {
Route route = new Route(ctx.getRoute());
route.setHop(0, hop);
ctx.addChild(route);
} else {
Reply reply = new EmptyReply();
reply.addError(new Error(ErrorCode.NO_ADDRESS_FOR_SERVICE,
"None of the configured recipients are currently available."));
ctx.setReply(reply);
}
}
// Inherit doc from RoutingPolicy.
public void merge(RoutingContext ctx) {
DocumentProtocol.merge(ctx);
}
/**
* Returns the appropriate recipient hop for the given routing context. This method provides synchronized access to
* the internal cache.
*
* @param ctx The routing context.
* @return The recipient hop to use.
*/
private synchronized Hop getRecipient(RoutingContext ctx) {
CacheEntry entry = update(ctx);
if (entry.recipients.isEmpty()) {
return null;
}
if (++entry.offset >= entry.recipients.size()) {
entry.offset = 0;
}
return new Hop(entry.recipients.get(entry.offset));
}
/**
* Updates and returns the cache entry for the given routing context. This method assumes that synchronization is
* handled outside of it.
*
* @param ctx The routing context.
* @return The updated cache entry.
*/
private CacheEntry update(RoutingContext ctx) {
String key = getCacheKey(ctx);
CacheEntry entry = cache.get(key);
if (entry == null) {
entry = new CacheEntry();
cache.put(key, entry);
}
int upd = ctx.getMirror().updates();
if (entry.generation != upd) {
entry.generation = upd;
entry.recipients.clear();
for (int i = 0; i < ctx.getNumRecipients(); ++i) {
List<Mirror.Entry> arr = ctx.getMirror().lookup(ctx.getRecipient(i).getHop(0).toString());
for (Mirror.Entry item : arr) {
entry.recipients.add(Hop.parse(item.getName()));
}
}
}
return entry;
}
/**
* Returns a cache key for this instance of the policy. Because behaviour is based on the recipient list of this
* policy, the cache key is the concatenated string of recipient routes.
*
* @param ctx The routing context.
* @return The cache key.
*/
private String getCacheKey(RoutingContext ctx) {
StringBuilder ret = new StringBuilder();
for (int i = 0; i < ctx.getNumRecipients(); ++i) {
ret.append(ctx.getRecipient(i).getHop(0).toString()).append(" ");
}
return ret.toString();
}
/**
* Defines the necessary cache data.
*/
private class CacheEntry {
private final List<Hop> recipients = new ArrayList<Hop>();
private int generation = 0;
private int offset = 0;
}
public void destroy() {
}
}
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