1/*
2 * Copyright (C) 2007 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
17package android.database.sqlite;
18
19import java.io.Closeable;
20
21/**
22 * An object created from a SQLiteDatabase that can be closed.
23 *
24 * This class implements a primitive reference counting scheme for database objects.
25 */
26public abstract class SQLiteClosable implements Closeable {
27    private int mReferenceCount = 1;
28
29    /**
30     * Called when the last reference to the object was released by
31     * a call to {@link #releaseReference()} or {@link #close()}.
32     */
33    protected abstract void onAllReferencesReleased();
34
35    /**
36     * Called when the last reference to the object was released by
37     * a call to {@link #releaseReferenceFromContainer()}.
38     *
39     * @deprecated Do not use.
40     */
41    @Deprecated
42    protected void onAllReferencesReleasedFromContainer() {
43        onAllReferencesReleased();
44    }
45
46    /**
47     * Acquires a reference to the object.
48     *
49     * @throws IllegalStateException if the last reference to the object has already
50     * been released.
51     */
52    public void acquireReference() {
53        synchronized(this) {
54            if (mReferenceCount <= 0) {
55                throw new IllegalStateException(
56                        "attempt to re-open an already-closed object: " + this);
57            }
58            mReferenceCount++;
59        }
60    }
61
62    /**
63     * Releases a reference to the object, closing the object if the last reference
64     * was released.
65     *
66     * @see #onAllReferencesReleased()
67     */
68    public void releaseReference() {
69        boolean refCountIsZero = false;
70        synchronized(this) {
71            refCountIsZero = --mReferenceCount == 0;
72        }
73        if (refCountIsZero) {
74            onAllReferencesReleased();
75        }
76    }
77
78    /**
79     * Releases a reference to the object that was owned by the container of the object,
80     * closing the object if the last reference was released.
81     *
82     * @see #onAllReferencesReleasedFromContainer()
83     * @deprecated Do not use.
84     */
85    @Deprecated
86    public void releaseReferenceFromContainer() {
87        boolean refCountIsZero = false;
88        synchronized(this) {
89            refCountIsZero = --mReferenceCount == 0;
90        }
91        if (refCountIsZero) {
92            onAllReferencesReleasedFromContainer();
93        }
94    }
95
96    /**
97     * Releases a reference to the object, closing the object if the last reference
98     * was released.
99     *
100     * Calling this method is equivalent to calling {@link #releaseReference}.
101     *
102     * @see #releaseReference()
103     * @see #onAllReferencesReleased()
104     */
105    public void close() {
106        releaseReference();
107    }
108}
109