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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 | +} | |