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// Copyright (C) 2019 The Android Open Source Project
//
// 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.gerrit.index.query;
import static java.util.Objects.requireNonNull;
import com.google.common.collect.ImmutableList;
import java.util.Iterator;
import java.util.function.Supplier;
/**
* Result set that allows for asynchronous execution of the actual query. Callers should dispatch
* the query and call the constructor of this class with a supplier that fetches the result and
* blocks on it if necessary.
*
* <p>If the execution is synchronous or the results are known a priori, consider using {@link
* ListResultSet}.
*/
public class LazyResultSet<T> implements ResultSet<T> {
private final Supplier<ImmutableList<T>> resultsCallback;
private boolean resultsReturned = false;
public LazyResultSet(Supplier<ImmutableList<T>> r) {
resultsCallback = requireNonNull(r, "results can't be null");
}
@Override
public Iterator<T> iterator() {
return toList().iterator();
}
@Override
public ImmutableList<T> toList() {
if (resultsReturned) {
throw new IllegalStateException("Results already obtained");
}
resultsReturned = true;
return resultsCallback.get();
}
@Override
public void close() {}
@Override
public Object searchAfter() {
return null;
}
}
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