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      1 /*
      2  * Copyright (C) 2014 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.camera.async;
     18 
     19 import com.google.common.annotations.VisibleForTesting;
     20 import com.google.common.base.Preconditions;
     21 
     22 /**
     23  * Wraps an object with reference counting. When the reference count goes to 0
     24  * for the first time, the object is closed.
     25  */
     26 public class RefCountBase<T extends SafeCloseable> implements SafeCloseable {
     27     private final Object mLock;
     28     private final T mObject;
     29     private int mRefCount;
     30     private boolean mObjectClosed;
     31 
     32     public RefCountBase(T object) {
     33         this(object, 1);
     34     }
     35 
     36     public RefCountBase(T object, int initialReferenceCount) {
     37         Preconditions.checkState(
     38                 initialReferenceCount > 0, "initialReferenceCount is not greater than 0.");
     39         mLock = new Object();
     40         mObject = object;
     41         mRefCount = initialReferenceCount;
     42         mObjectClosed = false;
     43     }
     44 
     45     public void addRef() {
     46         synchronized (mLock) {
     47             Preconditions.checkState(!mObjectClosed,
     48                     "addRef on an object which has been closed.");
     49             mRefCount++;
     50         }
     51     }
     52 
     53     public T get() {
     54         return mObject;
     55     }
     56 
     57     @Override
     58     public void close() {
     59         synchronized (mLock) {
     60             // A SafeCloseable must tolerate multiple calls to close().
     61             if (mObjectClosed) {
     62                 return;
     63             }
     64             mRefCount--;
     65             if (mRefCount > 0) {
     66                 return;
     67             }
     68             mObjectClosed = true;
     69         }
     70         // Do this outside of the mLock critical section for speed and to avoid
     71         // deadlock.
     72         mObject.close();
     73     }
     74 
     75     @VisibleForTesting
     76     public int getRefCount() {
     77         synchronized (mLock) {
     78             return mRefCount;
     79         }
     80     }
     81 }
     82