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      1 /*
      2  * Copyright (C) 2017 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.ahat.heapdump;
     18 
     19 import java.util.Comparator;
     20 import java.util.Iterator;
     21 import java.util.List;
     22 
     23 /**
     24  * A collection of instances that can be searched for by id.
     25  */
     26 class Instances<T extends AhatInstance> implements Iterable<T> {
     27 
     28   private final List<T> mInstances;
     29 
     30   /**
     31    * Create a collection of instances that can be looked up by id.
     32    * Note: this takes ownership of the given list of instances.
     33    */
     34   public Instances(List<T> instances) {
     35     mInstances = instances;
     36 
     37     // Sort the instances by id so we can use binary search to lookup
     38     // instances by id.
     39     instances.sort(new Comparator<AhatInstance>() {
     40       @Override
     41       public int compare(AhatInstance a, AhatInstance b) {
     42         return Long.compare(a.getId(), b.getId());
     43       }
     44     });
     45   }
     46 
     47   /**
     48    * Look up an instance by id.
     49    * Returns null if no instance with the given id is found.
     50    */
     51   public T get(long id) {
     52     // Binary search over the sorted instances.
     53     int start = 0;
     54     int end = mInstances.size();
     55     while (start < end) {
     56       int mid = start + ((end - start) / 2);
     57       T midInst = mInstances.get(mid);
     58       long midId = midInst.getId();
     59       if (id == midId) {
     60         return midInst;
     61       } else if (id < midId) {
     62         end = mid;
     63       } else {
     64         start = mid + 1;
     65       }
     66     }
     67     return null;
     68   }
     69 
     70   @Override
     71   public Iterator<T> iterator() {
     72     return mInstances.iterator();
     73   }
     74 }
     75 
     76