| // 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 com.google.common.base.Preconditions; |
| import javax.annotation.Nullable; |
| |
| /** Supplier that may throw {@link InterruptedException} when value is retrieved. */ |
| public interface InterruptibleSupplier<T> { |
| T get() throws InterruptedException; |
| |
| /** Memoizes the result of {@code delegate} after the first call to {@link #get}. */ |
| final class Memoize<T> implements InterruptibleSupplier<T> { |
| private InterruptibleSupplier<T> delegate; |
| @Nullable private volatile T value = null; |
| |
| private Memoize(InterruptibleSupplier<T> delegate) { |
| this.delegate = Preconditions.checkNotNull(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(); |
| delegate = null; // Free up for GC. |
| } |
| } |
| return value; |
| } |
| } |
| } |