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| 1 | /* | ||
| 2 | * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.nio; | ||
| 27 | |||
| 28 | import java.io.FileDescriptor; | ||
| 29 | import sun.misc.Unsafe; | ||
| 30 | |||
| 31 | |||
| 32 | /** | ||
| 33 | * A direct byte buffer whose content is a memory-mapped region of a file. | ||
| 34 | * | ||
| 35 | * <p> Mapped byte buffers are created via the {@link | ||
| 36 | * java.nio.channels.FileChannel#map FileChannel.map} method. This class | ||
| 37 | * extends the {@link ByteBuffer} class with operations that are specific to | ||
| 38 | * memory-mapped file regions. | ||
| 39 | * | ||
| 40 | * <p> A mapped byte buffer and the file mapping that it represents remain | ||
| 41 | * valid until the buffer itself is garbage-collected. | ||
| 42 | * | ||
| 43 | * <p> The content of a mapped byte buffer can change at any time, for example | ||
| 44 | * if the content of the corresponding region of the mapped file is changed by | ||
| 45 | * this program or another. Whether or not such changes occur, and when they | ||
| 46 | * occur, is operating-system dependent and therefore unspecified. | ||
| 47 | * | ||
| 48 | * <a name="inaccess"><p> All or part of a mapped byte buffer may become | ||
| 49 | * inaccessible at any time, for example if the mapped file is truncated. An | ||
| 50 | * attempt to access an inaccessible region of a mapped byte buffer will not | ||
| 51 | * change the buffer's content and will cause an unspecified exception to be | ||
| 52 | * thrown either at the time of the access or at some later time. It is | ||
| 53 | * therefore strongly recommended that appropriate precautions be taken to | ||
| 54 | * avoid the manipulation of a mapped file by this program, or by a | ||
| 55 | * concurrently running program, except to read or write the file's content. | ||
| 56 | * | ||
| 57 | * <p> Mapped byte buffers otherwise behave no differently than ordinary direct | ||
| 58 | * byte buffers. </p> | ||
| 59 | * | ||
| 60 | * | ||
| 61 | * @author Mark Reinhold | ||
| 62 | * @author JSR-51 Expert Group | ||
| 63 | * @since 1.4 | ||
| 64 | */ | ||
| 65 | |||
| 66 | public abstract class MappedByteBuffer | ||
| 67 | extends ByteBuffer | ||
| 68 | { | ||
| 69 | |||
| 70 | // This is a little bit backwards: By rights MappedByteBuffer should be a | ||
| 71 | // subclass of DirectByteBuffer, but to keep the spec clear and simple, and | ||
| 72 | // for optimization purposes, it's easier to do it the other way around. | ||
| 73 | // This works because DirectByteBuffer is a package-private class. | ||
| 74 | |||
| 75 | // For mapped buffers, a FileDescriptor that may be used for mapping | ||
| 76 | // operations if valid; null if the buffer is not mapped. | ||
| 77 | private final FileDescriptor fd; | ||
| 78 | |||
| 79 | // This should only be invoked by the DirectByteBuffer constructors | ||
| 80 | // | ||
| 81 | MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private | ||
| 82 | FileDescriptor fd) | ||
| 83 | { | ||
| 84 | super(mark, pos, lim, cap); | ||
| 85 | this.fd = fd; | ||
| 86 | } | ||
| 87 | |||
| 88 | MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private | ||
| 89 | super(mark, pos, lim, cap); | ||
| 90 | this.fd = null; | ||
| 91 | } | ||
| 92 | |||
| 93 | private void checkMapped() { | ||
| 94 | if (fd == null) | ||
| 95 | // Can only happen if a luser explicitly casts a direct byte buffer | ||
| 96 | throw new UnsupportedOperationException(); | ||
| 97 | } | ||
| 98 | |||
| 99 | // Returns the distance (in bytes) of the buffer from the page aligned address | ||
| 100 | // of the mapping. Computed each time to avoid storing in every direct buffer. | ||
| 101 | private long mappingOffset() { | ||
| 102 | int ps = Bits.pageSize(); | ||
| 103 | long offset = address % ps; | ||
| 104 | return (offset >= 0) ? offset : (ps + offset); | ||
| 105 | } | ||
| 106 | |||
| 107 | private long mappingAddress(long mappingOffset) { | ||
| 108 | return address - mappingOffset; | ||
| 109 | } | ||
| 110 | |||
| 111 | private long mappingLength(long mappingOffset) { | ||
| 112 | return (long)capacity() + mappingOffset; | ||
| 113 | } | ||
| 114 | |||
| 115 | /** | ||
| 116 | * Tells whether or not this buffer's content is resident in physical | ||
| 117 | * memory. | ||
| 118 | * | ||
| 119 | * <p> A return value of <tt>true</tt> implies that it is highly likely | ||
| 120 | * that all of the data in this buffer is resident in physical memory and | ||
| 121 | * may therefore be accessed without incurring any virtual-memory page | ||
| 122 | * faults or I/O operations. A return value of <tt>false</tt> does not | ||
| 123 | * necessarily imply that the buffer's content is not resident in physical | ||
| 124 | * memory. | ||
| 125 | * | ||
| 126 | * <p> The returned value is a hint, rather than a guarantee, because the | ||
| 127 | * underlying operating system may have paged out some of the buffer's data | ||
| 128 | * by the time that an invocation of this method returns. </p> | ||
| 129 | * | ||
| 130 | * @return <tt>true</tt> if it is likely that this buffer's content | ||
| 131 | * is resident in physical memory | ||
| 132 | */ | ||
| 133 | public final boolean isLoaded() { | ||
| 134 | checkMapped(); | ||
| 135 | if ((address == 0) || (capacity() == 0)) | ||
| 136 | return true; | ||
| 137 | long offset = mappingOffset(); | ||
| 138 | long length = mappingLength(offset); | ||
| 139 | return isLoaded0(mappingAddress(offset), length, Bits.pageCount(length)); | ||
| 140 | } | ||
| 141 | |||
| 142 | /** | ||
| 143 | * Loads this buffer's content into physical memory. | ||
| 144 | * | ||
| 145 | * <p> This method makes a best effort to ensure that, when it returns, | ||
| 146 | * this buffer's content is resident in physical memory. Invoking this | ||
| 147 | * method may cause some number of page faults and I/O operations to | ||
| 148 | * occur. </p> | ||
| 149 | * | ||
| 150 | * @return This buffer | ||
| 151 | */ | ||
| 152 | public final MappedByteBuffer load() { | ||
| 153 | checkMapped(); | ||
| 154 | if ((address == 0) || (capacity() == 0)) | ||
| 155 | return this; | ||
| 156 | long offset = mappingOffset(); | ||
| 157 | long length = mappingLength(offset); | ||
| 158 | load0(mappingAddress(offset), length); | ||
| 159 | |||
| 160 | // touch each page | ||
| 161 | Unsafe unsafe = Unsafe.getUnsafe(); | ||
| 162 | int ps = Bits.pageSize(); | ||
| 163 | int count = Bits.pageCount(length); | ||
| 164 | long a = mappingAddress(offset); | ||
| 165 | for (int i=0; i<count; i++) { | ||
| 166 | unsafe.getByte(a); | ||
| 167 | a += ps; | ||
| 168 | } | ||
| 169 | |||
| 170 | return this; | ||
| 171 | } | ||
| 172 | |||
| 173 | /** | ||
| 174 | * Forces any changes made to this buffer's content to be written to the | ||
| 175 | * storage device containing the mapped file. | ||
| 176 | * | ||
| 177 | * <p> If the file mapped into this buffer resides on a local storage | ||
| 178 | * device then when this method returns it is guaranteed that all changes | ||
| 179 | * made to the buffer since it was created, or since this method was last | ||
| 180 | * invoked, will have been written to that device. | ||
| 181 | * | ||
| 182 | * <p> If the file does not reside on a local device then no such guarantee | ||
| 183 | * is made. | ||
| 184 | * | ||
| 185 | * <p> If this buffer was not mapped in read/write mode ({@link | ||
| 186 | * java.nio.channels.FileChannel.MapMode#READ_WRITE}) then invoking this | ||
| 187 | * method has no effect. </p> | ||
| 188 | * | ||
| 189 | * @return This buffer | ||
| 190 | */ | ||
| 191 | public final MappedByteBuffer force() { | ||
| 192 | checkMapped(); | ||
| 193 | if ((address != 0) && (capacity() != 0)) { | ||
| 194 | long offset = mappingOffset(); | ||
| 195 | force0(fd, mappingAddress(offset), mappingLength(offset)); | ||
| 196 | } | ||
| 197 | return this; | ||
| 198 | } | ||
| 199 | |||
| 200 | private native boolean isLoaded0(long address, long length, int pageCount); | ||
| 201 | private native void load0(long address, long length); | ||
| 202 | private native void force0(FileDescriptor fd, long address, long length); | ||
| 203 | } | ||