1/*
2 * Copyright (C) 2015 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.os;
18
19import java.util.HashMap;
20
21/**
22 * Helper class for writing pooled strings into a Parcel.  It must be used
23 * in conjunction with {@link android.os.PooledStringReader}.  This really needs
24 * to be pushed in to Parcel itself, but doing that is...  complicated.
25 * @hide
26 */
27public class PooledStringWriter {
28    private final Parcel mOut;
29
30    /**
31     * Book-keeping for writing pooled string objects, mapping strings we have
32     * written so far to their index in the pool.  We deliberately use HashMap
33     * here since performance is critical, we expect to be doing lots of adds to
34     * it, and it is only a temporary object so its overall memory footprint is
35     * not a signifciant issue.
36     */
37    private final HashMap<String, Integer> mPool;
38
39    /**
40     * Book-keeping for writing pooling string objects, indicating where we
41     * started writing the pool, which is where we need to ultimately store
42     * how many strings are in the pool.
43     */
44    private int mStart;
45
46    /**
47     * Next available index in the pool.
48     */
49    private int mNext;
50
51    public PooledStringWriter(Parcel out) {
52        mOut = out;
53        mPool = new HashMap<>();
54        mStart = out.dataPosition();
55        out.writeInt(0); // reserve space for final pool size.
56    }
57
58    public void writeString(String str) {
59        final Integer cur = mPool.get(str);
60        if (cur != null) {
61            mOut.writeInt(cur);
62        } else {
63            mPool.put(str, mNext);
64            mOut.writeInt(-(mNext+1));
65            mOut.writeString(str);
66            mNext++;
67        }
68    }
69
70    public int getStringCount() {
71        return mPool.size();
72    }
73
74    public void finish() {
75        final int pos = mOut.dataPosition();
76        mOut.setDataPosition(mStart);
77        mOut.writeInt(mNext);
78        mOut.setDataPosition(pos);
79    }
80}
81