1/* Licensed to the Apache Software Foundation (ASF) under one or more 2 * contributor license agreements. See the NOTICE file distributed with 3 * this work for additional information regarding copyright ownership. 4 * The ASF licenses this file to You under the Apache License, Version 2.0 5 * (the "License"); you may not use this file except in compliance with 6 * the License. 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 java.nio; 18 19import java.nio.channels.FileChannel.MapMode; 20import libcore.io.ErrnoException; 21import libcore.io.Libcore; 22import libcore.io.Memory; 23import static libcore.io.OsConstants.*; 24 25/** 26 * {@code MappedByteBuffer} is a special kind of direct byte buffer which maps a 27 * region of file to memory. 28 * <p> 29 * {@code MappedByteBuffer} can be created by calling 30 * {@link java.nio.channels.FileChannel#map(java.nio.channels.FileChannel.MapMode, long, long) FileChannel.map}. 31 * Once created, the mapping between the byte buffer and the file region remains 32 * valid until the byte buffer is garbage collected. 33 * <p> 34 * All or part of a {@code MappedByteBuffer}'s content may change or become 35 * inaccessible at any time, since the mapped file region can be modified by 36 * another thread or process at any time. If this happens, the behavior of the 37 * {@code MappedByteBuffer} is undefined. 38 */ 39public abstract class MappedByteBuffer extends ByteBuffer { 40 41 final DirectByteBuffer wrapped; 42 43 private final MapMode mapMode; 44 45 MappedByteBuffer(ByteBuffer directBuffer) { 46 super(directBuffer.capacity, directBuffer.block); 47 if (!directBuffer.isDirect()) { 48 throw new IllegalArgumentException("directBuffer is not a direct buffer: " + directBuffer); 49 } 50 this.wrapped = (DirectByteBuffer) directBuffer; 51 this.mapMode = null; 52 } 53 54 MappedByteBuffer(MemoryBlock block, int capacity, int offset, MapMode mapMode) { 55 super(capacity, block); 56 this.mapMode = mapMode; 57 if (mapMode == MapMode.READ_ONLY) { 58 wrapped = new ReadOnlyDirectByteBuffer(block, capacity, offset); 59 } else { 60 wrapped = new ReadWriteDirectByteBuffer(block, capacity, offset); 61 } 62 } 63 64 /** 65 * Returns true if there is a high probability that every page of this buffer is currently 66 * loaded in RAM, meaning that accesses will not cause a page fault. It is impossible to give 67 * a strong guarantee since this is only a snapshot of a dynamic situation. 68 */ 69 public final boolean isLoaded() { 70 long address = block.toInt(); 71 long size = block.getSize(); 72 if (size == 0) { 73 return true; 74 } 75 76 try { 77 int pageSize = (int) Libcore.os.sysconf(_SC_PAGE_SIZE); 78 int pageOffset = (int) (address % pageSize); 79 address -= pageOffset; 80 size += pageOffset; 81 int pageCount = (int) ((size + pageSize - 1) / pageSize); 82 byte[] vector = new byte[pageCount]; 83 Libcore.os.mincore(address, size, vector); 84 for (int i = 0; i < vector.length; ++i) { 85 if ((vector[i] & 1) != 1) { 86 return false; 87 } 88 } 89 return true; 90 } catch (ErrnoException errnoException) { 91 return false; 92 } 93 } 94 95 /** 96 * Attempts to load every page of this buffer into RAM. See {@link #isLoaded}. 97 * @return this buffer. 98 */ 99 public final MappedByteBuffer load() { 100 try { 101 Libcore.os.mlock(block.toInt(), block.getSize()); 102 Libcore.os.munlock(block.toInt(), block.getSize()); 103 } catch (ErrnoException ignored) { 104 } 105 return this; 106 } 107 108 /** 109 * Writes all changes of the buffer to the mapped file. If the mapped file 110 * is stored on a local device, it is guaranteed that the changes are 111 * written to the file. No such guarantee is given if the file is located on 112 * a remote device. 113 * 114 * @return this buffer. 115 */ 116 public final MappedByteBuffer force() { 117 if (mapMode == MapMode.READ_WRITE) { 118 try { 119 Libcore.os.msync(block.toInt(), block.getSize(), MS_SYNC); 120 } catch (ErrnoException errnoException) { 121 // The RI doesn't throw, presumably on the assumption that you can't get into 122 // a state where msync(2) could return an error. 123 throw new AssertionError(errnoException); 124 } 125 } 126 return this; 127 } 128} 129