| /* |
| * Copyright (C) 2016 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.android.tools.build.apkzlib.utils; |
| |
| import java.util.function.Supplier; |
| import javax.annotation.Nonnull; |
| |
| /** |
| * Supplier that will cache a computed value and always supply the same value. It can be used to |
| * lazily compute data. For example: |
| * |
| * <pre>{@code |
| * CachedSupplier<Integer> value = new CachedSupplier<>(() -> { |
| * Integer result; |
| * // Do some expensive computation. |
| * return result; |
| * }); |
| * |
| * if (a) { |
| * // We need the result of the expensive computation. |
| * Integer r = value.get(); |
| * } |
| * |
| * if (b) { |
| * // We also need the result of the expensive computation. |
| * Integer r = value.get(); |
| * } |
| * |
| * // If neither a nor b are true, we avoid doing the computation at all. |
| * }</pre> |
| */ |
| public class CachedSupplier<T> { |
| |
| /** |
| * The cached data, {@code null} if computation resulted in {@code null}. It is also |
| * {@code null} if the cached data has not yet been computed. |
| */ |
| private T cached; |
| |
| /** |
| * Is the current data in {@link #cached} valid? |
| */ |
| private boolean valid; |
| |
| /** |
| * Actual supplier of data, if computation is needed. |
| */ |
| @Nonnull |
| private final Supplier<T> supplier; |
| |
| /** |
| * Creates a new supplier. |
| */ |
| public CachedSupplier(@Nonnull Supplier<T> supplier) { |
| valid = false; |
| this.supplier = supplier; |
| } |
| |
| |
| /** |
| * Obtains the value. |
| * |
| * @return the value, either cached (if one exists) or computed |
| */ |
| public synchronized T get() { |
| if (!valid) { |
| cached = supplier.get(); |
| valid = true; |
| } |
| |
| return cached; |
| } |
| |
| /** |
| * Resets the cache forcing a {@code get()} on the supplier next time {@link #get()} is invoked. |
| */ |
| public synchronized void reset() { |
| cached = null; |
| valid = false; |
| } |
| |
| /** |
| * In some cases, we may be able to precompute the cache value (or load it from somewhere we |
| * had previously stored it). This method allows the cache value to be loaded. |
| * |
| * <p>If this method is invoked, then an invocation of {@link #get()} will not trigger an |
| * invocation of the supplier provided in the constructor. |
| * |
| * @param t the new cache contents; will replace any currently cache content, if one exists |
| */ |
| public synchronized void precomputed(T t) { |
| cached = t; |
| valid = true; |
| } |
| |
| /** |
| * Checks if the contents of the cache are valid. |
| * |
| * @return are there valid contents in the cache? |
| */ |
| public synchronized boolean isValid() { |
| return valid; |
| } |
| } |