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 
RefCountBase(T object)32     public RefCountBase(T object) {
33         this(object, 1);
34     }
35 
RefCountBase(T object, int initialReferenceCount)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 
addRef()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 
get()53     public T get() {
54         return mObject;
55     }
56 
57     @Override
close()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
getRefCount()76     public int getRefCount() {
77         synchronized (mLock) {
78             return mRefCount;
79         }
80     }
81 }
82