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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.skyframe;
import javax.annotation.Nullable;
/** Supplier that may throw {@link InterruptedException} when value is retrieved. */
public interface InterruptibleSupplier<T> {
T get() throws InterruptedException;
class Instance<T> implements InterruptibleSupplier<T> {
private final T instance;
public Instance(T instance) {
this.instance = instance;
}
@Override
public T get() {
return instance;
}
}
class Memoize<T> implements InterruptibleSupplier<T> {
private final InterruptibleSupplier<T> delegate;
private @Nullable T value = null;
private Memoize(InterruptibleSupplier<T> delegate) {
this.delegate = delegate;
}
public static <S> InterruptibleSupplier<S> of(InterruptibleSupplier<S> delegate) {
if (delegate instanceof Memoize) {
return delegate;
}
return new Memoize<>(delegate);
}
@Override
public T get() throws InterruptedException {
if (value != null) {
return value;
}
synchronized (this) {
if (value == null) {
value = delegate.get();
}
}
return value;
}
}
}
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