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// Copyright 2014 The Bazel Authors. All rights reserved.
//
// Licensed 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,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.lib.query2.engine;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Sets;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.Argument;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.ArgumentType;
import com.google.devtools.build.lib.query2.engine.QueryEnvironment.QueryFunction;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* Implementation of the <code>allpaths()</code> function.
*/
public class AllPathsFunction implements QueryFunction {
AllPathsFunction() {
}
@Override
public String getName() {
return "allpaths";
}
@Override
public int getMandatoryArguments() {
return 2;
}
@Override
public List<ArgumentType> getArgumentTypes() {
return ImmutableList.of(ArgumentType.EXPRESSION, ArgumentType.EXPRESSION);
}
@Override
public <T> Set<T> eval(QueryEnvironment<T> env, QueryExpression expression, List<Argument> args)
throws QueryException, InterruptedException {
QueryExpression from = args.get(0).getExpression();
QueryExpression to = args.get(1).getExpression();
Set<T> fromValue = from.eval(env);
Set<T> toValue = to.eval(env);
// Algorithm: compute "reachableFromX", the forward transitive closure of
// the "from" set, then find the intersection of "reachableFromX" with the
// reverse transitive closure of the "to" set. The reverse transitive
// closure and intersection operations are interleaved for efficiency.
// "result" holds the intersection.
env.buildTransitiveClosure(expression, fromValue, Integer.MAX_VALUE);
Set<T> reachableFromX = env.getTransitiveClosure(fromValue);
Set<T> result = intersection(reachableFromX, toValue);
Collection<T> worklist = result;
while (!worklist.isEmpty()) {
Collection<T> reverseDeps = env.getReverseDeps(worklist);
worklist = new ArrayList<>();
for (T np : reverseDeps) {
if (reachableFromX.contains(np) && result.add(np)) {
worklist.add(np);
}
}
}
return result;
}
/**
* Returns a (new, mutable, unordered) set containing the intersection of the
* two specified sets.
*/
private static <T> Set<T> intersection(Set<T> x, Set<T> y) {
Set<T> result = new HashSet<>();
if (x.size() > y.size()) {
Sets.intersection(y, x).copyInto(result);
} else {
Sets.intersection(x, y).copyInto(result);
}
return result;
}
}
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