/*
* Copyright 2016-present Facebook, Inc.
*
* 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.facebook.buck.util;
import com.google.common.base.Supplier;
import java.lang.ref.WeakReference;
import javax.annotation.Nullable;
public final class MoreSuppliers {
private MoreSuppliers() {}
public static <T> Supplier<T> weakMemoize(Supplier<T> delegate) {
return (delegate instanceof WeakMemoizingSupplier)
? delegate
: new WeakMemoizingSupplier<>(delegate);
}
private static class WeakMemoizingSupplier<T> implements Supplier<T> {
private final Supplier<T> delegate;
private WeakReference<T> valueRef;
public WeakMemoizingSupplier(Supplier<T> delegate) {
this.delegate = delegate;
this.valueRef = new WeakReference<>(null);
}
@Override
public T get() {
@Nullable T value = valueRef.get();
if (value == null) {
synchronized (this) {
// Check again in case someone else has populated the cache.
value = valueRef.get();
if (value == null) {
value = delegate.get();
valueRef = new WeakReference<>(value);
}
}
}
return value;
}
}
}