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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.messagebus.routing;
/**
* Decides how to choose between candidate recipients of a hop template point.
* <p>
* The routing policy will be given an address and a set of recipients matching this address. It is responsible for
* choosing one of the given recipients each time {@link #select} is called. The routing policy chooses which recipient
* to return each time at its sole discretion, using information in the RoutingContext argument to choose or not as required
* to implement the policy.
* <p>
* Example:
* <ul>
* <li>The given <i>address</i> is <code>a/b/?</code>
* <li>The given <i>recipients</i> are <code>a/b/c, a/b/d and a/b/e</code> - one of these three must be returned on every call to <code>choose</code>
* </ul>
* <p>
* This class is pluggable per template point in the address of a hop.
*
* @author bratseth
* @author Simon Thoresen Hult
*/
public interface RoutingPolicy {
/**
* This function must choose a set of services that is to receive the given message from a list of possible
* recipients. This is done by adding child routing contexts to the argument object. These children can then be
* iterated and manipulated even before selection pass is concluded.
*
* @param context the complete context for the invocation of this policy. Contains all available data.
*/
void select(RoutingContext context);
/**
* This function is called when all replies have arrived for some message. The implementation is responsible for
* merging multiple replies into a single sensible reply. The replies is contained in the child context objects of
* the argument context, and then response must be set in that context.
*
* @param context the complete context for the invocation of this policy. Contains all available data.
*/
void merge(RoutingContext context);
/**
* Destroys this factory and frees up any resources it has held. Making further calls on a destroyed
* factory causes a runtime exception.
*/
void destroy();
}
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