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// Copyright 2016 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.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
import java.util.concurrent.ForkJoinPool;
/** Listener for calls to the internal methods of {@link QueryExpression} used for evaluation. */
@ThreadSafe
public interface QueryExpressionEvalListener<T> {
/** Called right before {@link QueryExpression#evalImpl} is called. */
void onEval(
QueryExpression expr,
QueryEnvironment<T> env,
VariableContext<T> context,
Callback<T> callback);
/** Called right before {@link QueryExpression#parEvalImpl} is called. */
void onParEval(
QueryExpression expr,
QueryEnvironment<T> env,
VariableContext<T> context,
ThreadSafeCallback<T> callback,
ForkJoinPool forkJoinPool);
/** A {@link QueryExpressionEvalListener} that does nothing. */
class NullListener<T> implements QueryExpressionEvalListener<T> {
private static final NullListener<?> INSTANCE = new NullListener<>();
private NullListener() {
}
@SuppressWarnings("unchecked")
public static <T> NullListener<T> instance() {
return (NullListener<T>) INSTANCE;
}
@Override
public void onEval(
QueryExpression expr,
QueryEnvironment<T> env,
VariableContext<T> context,
Callback<T> callback) {
}
@Override
public void onParEval(
QueryExpression expr,
QueryEnvironment<T> env,
VariableContext<T> context,
ThreadSafeCallback<T> callback,
ForkJoinPool forkJoinPool) {
}
}
}
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