org.apache.hadoop.hive.ql.lib.DefaultRuleDispatcher Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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*/
package org.apache.hadoop.hive.ql.lib;
import java.util.Map;
import java.util.Stack;
import org.apache.hadoop.hive.ql.parse.SemanticException;
/**
* Dispatches calls to relevant method in processor. The user registers various
* rules with the dispatcher, and the processor corresponding to closest
* matching rule is fired.
*/
public class DefaultRuleDispatcher implements Dispatcher {
private final Map procRules;
private final NodeProcessorCtx procCtx;
private final NodeProcessor defaultProc;
/**
* Constructor.
*
* @param defaultProc
* default processor to be fired if no rule matches
* @param rules
* operator processor that handles actual processing of the node
* @param procCtx
* operator processor context, which is opaque to the dispatcher
*/
public DefaultRuleDispatcher(NodeProcessor defaultProc,
Map rules, NodeProcessorCtx procCtx) {
this.defaultProc = defaultProc;
procRules = rules;
this.procCtx = procCtx;
}
/**
* Dispatcher function.
*
* @param nd
* operator to process
* @param ndStack
* the operators encountered so far
* @throws SemanticException
*/
@Override
public Object dispatch(Node nd, Stack ndStack, Object... nodeOutputs)
throws SemanticException {
// find the firing rule
// find the rule from the stack specified
Rule rule = null;
int minCost = Integer.MAX_VALUE;
for (Rule r : procRules.keySet()) {
int cost = r.cost(ndStack);
if ((cost >= 0) && (cost <= minCost)) {
minCost = cost;
rule = r;
}
}
NodeProcessor proc;
if (rule == null) {
proc = defaultProc;
} else {
proc = procRules.get(rule);
}
// Do nothing in case proc is null
if (proc != null) {
// Call the process function
return proc.process(nd, ndStack, procCtx, nodeOutputs);
} else {
return null;
}
}
}