ByteArrayRingBuffer.java revision cc84bc6179db408b1e45168d43e10ba0ab089fca 
1/*
2 * Copyright (C) 2016 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 com.android.server.wifi.util;
18
19import java.util.ArrayList;
20
21/**
22 * A ring buffer where each element of the ring is itself a byte array.
23 */
24public class ByteArrayRingBuffer {
25    private ArrayList<byte[]> mArrayList;
26    private final int mMaxBytes;
27    private int mBytesUsed;
28
29    /**
30     * Creates a ring buffer that holds at most |maxBytes| of data. The overhead for each element
31     * is not included in this limit.
32     * @param maxBytes upper bound on the amount of data held
33     */
34    public ByteArrayRingBuffer(int maxBytes) {
35        mArrayList = new ArrayList<byte[]>();
36        mMaxBytes = maxBytes;
37        mBytesUsed = 0;
38    }
39
40    /**
41     * Adds |newData| to the ring buffer. Removes existing entries to make room, if necessary.
42     * Existing entries are removed in FIFO order.
43     * <p><b>Note:</b> will fail if |newData| itself exceeds the size limit for this buffer.
44     * Will first remove all existing entries in this case. (This guarantees that the ring buffer
45     * always represents a contiguous sequence of data.)
46     * @param newData data to be added to the ring
47     * @return true if the data was added
48     */
49    public boolean appendBuffer(byte[] newData) {
50        // Loop is O(n^2), but |n| is expected to be small.
51        while (mBytesUsed + newData.length > mMaxBytes
52                && !mArrayList.isEmpty()) {
53            mBytesUsed -= mArrayList.get(0).length;
54            mArrayList.remove(0);
55        }
56
57        if (mBytesUsed + newData.length > mMaxBytes) {
58            return false;
59        }
60
61        mArrayList.add(newData);
62        mBytesUsed += newData.length;
63        return true;
64    }
65
66    /**
67     * Returns the |i|-th element of the ring. The element retains its position in the ring.
68     * @param i
69     * @return the requested element
70     */
71    public byte[] getBuffer(int i) {
72        return mArrayList.get(i);
73    }
74
75    /**
76     * Returns the number of elements present in the ring.
77     * @return the number of elements present
78     */
79    public int getNumBuffers() {
80        return mArrayList.size();
81    }
82}
83