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      1 /*
      2  * Copyright (C) 2018 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.server.wm.utils;
     18 
     19 import android.util.SparseArray;
     20 
     21 import java.util.Arrays;
     22 
     23 /**
     24  * Caches the result of a rotation-dependent computation.
     25  *
     26  * The cache is discarded once the identity of the other parameter changes.
     27  *
     28  * @param <T> type of the parameter to the computation
     29  * @param <R> type of the result of the computation
     30  */
     31 public class RotationCache<T,R> {
     32 
     33     private final RotationDependentComputation<T,R> mComputation;
     34     private final SparseArray<R> mCache = new SparseArray<>(4);
     35     private T mCachedFor;
     36 
     37     public RotationCache(RotationDependentComputation<T, R> computation) {
     38         mComputation = computation;
     39     }
     40 
     41     /**
     42      * Looks up the result of the computation, or calculates it if needed.
     43      *
     44      * @param t a parameter to the rotation-dependent computation.
     45      * @param rotation the rotation for which to perform the rotation-dependent computation.
     46      * @return the result of the rotation-dependent computation.
     47      */
     48     public R getOrCompute(T t, int rotation) {
     49         if (t != mCachedFor) {
     50             mCache.clear();
     51             mCachedFor = t;
     52         }
     53         final int idx = mCache.indexOfKey(rotation);
     54         if (idx >= 0) {
     55             return mCache.valueAt(idx);
     56         }
     57         final R result = mComputation.compute(t, rotation);
     58         mCache.put(rotation, result);
     59         return result;
     60     }
     61 
     62     /**
     63      * A computation that takes a generic input and is dependent on the rotation. The result can
     64      * be cached by {@link RotationCache}.
     65      */
     66     @FunctionalInterface
     67     public interface RotationDependentComputation<T, R> {
     68         R compute(T t, int rotation);
     69     }
     70 }
     71