ByteArrayRingBuffer.java revision cc84bc6179db408b1e45168d43e10ba0ab089fca
1cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal/* 2cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Copyright (C) 2016 The Android Open Source Project 3cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * 4cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Licensed under the Apache License, Version 2.0 (the "License"); 5cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * you may not use this file except in compliance with the License. 6cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * You may obtain a copy of the License at 7cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * 8cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * http://www.apache.org/licenses/LICENSE-2.0 9cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * 10cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Unless required by applicable law or agreed to in writing, software 11cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * distributed under the License is distributed on an "AS IS" BASIS, 12cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * See the License for the specific language governing permissions and 14cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * limitations under the License. 15cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 16cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 17cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawalpackage com.android.server.wifi.util; 18cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 19cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawalimport java.util.ArrayList; 20cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 21cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal/** 22cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * A ring buffer where each element of the ring is itself a byte array. 23cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 24cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawalpublic class ByteArrayRingBuffer { 25cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal private ArrayList<byte[]> mArrayList; 26cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal private final int mMaxBytes; 27cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal private int mBytesUsed; 28cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 29cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal /** 30cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Creates a ring buffer that holds at most |maxBytes| of data. The overhead for each element 31cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * is not included in this limit. 32cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @param maxBytes upper bound on the amount of data held 33cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 34cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal public ByteArrayRingBuffer(int maxBytes) { 35cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mArrayList = new ArrayList<byte[]>(); 36cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mMaxBytes = maxBytes; 37cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mBytesUsed = 0; 38cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 39cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 40cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal /** 41cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Adds |newData| to the ring buffer. Removes existing entries to make room, if necessary. 42cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Existing entries are removed in FIFO order. 43cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * <p><b>Note:</b> will fail if |newData| itself exceeds the size limit for this buffer. 44cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Will first remove all existing entries in this case. (This guarantees that the ring buffer 45cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * always represents a contiguous sequence of data.) 46cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @param newData data to be added to the ring 47cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @return true if the data was added 48cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 49cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal public boolean appendBuffer(byte[] newData) { 50cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal // Loop is O(n^2), but |n| is expected to be small. 51cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal while (mBytesUsed + newData.length > mMaxBytes 52cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal && !mArrayList.isEmpty()) { 53cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mBytesUsed -= mArrayList.get(0).length; 54cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mArrayList.remove(0); 55cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 56cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 57cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal if (mBytesUsed + newData.length > mMaxBytes) { 58cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal return false; 59cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 60cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 61cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mArrayList.add(newData); 62cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal mBytesUsed += newData.length; 63cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal return true; 64cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 65cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 66cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal /** 67cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Returns the |i|-th element of the ring. The element retains its position in the ring. 68cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @param i 69cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @return the requested element 70cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 71cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal public byte[] getBuffer(int i) { 72cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal return mArrayList.get(i); 73cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 74cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal 75cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal /** 76cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * Returns the number of elements present in the ring. 77cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal * @return the number of elements present 78cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal */ 79cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal public int getNumBuffers() { 80cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal return mArrayList.size(); 81cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal } 82cc84bc6179db408b1e45168d43e10ba0ab089fcamukesh agrawal} 83