J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2000-2003 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.nio; |
| 27 | |
| 28 | |
| 29 | /** |
| 30 | * A direct byte buffer whose content is a memory-mapped region of a file. |
| 31 | * |
| 32 | * <p> Mapped byte buffers are created via the {@link |
| 33 | * java.nio.channels.FileChannel#map FileChannel.map} method. This class |
| 34 | * extends the {@link ByteBuffer} class with operations that are specific to |
| 35 | * memory-mapped file regions. |
| 36 | * |
| 37 | * <p> A mapped byte buffer and the file mapping that it represents remain |
| 38 | * valid until the buffer itself is garbage-collected. |
| 39 | * |
| 40 | * <p> The content of a mapped byte buffer can change at any time, for example |
| 41 | * if the content of the corresponding region of the mapped file is changed by |
| 42 | * this program or another. Whether or not such changes occur, and when they |
| 43 | * occur, is operating-system dependent and therefore unspecified. |
| 44 | * |
| 45 | * <a name="inaccess"><p> All or part of a mapped byte buffer may become |
| 46 | * inaccessible at any time, for example if the mapped file is truncated. An |
| 47 | * attempt to access an inaccessible region of a mapped byte buffer will not |
| 48 | * change the buffer's content and will cause an unspecified exception to be |
| 49 | * thrown either at the time of the access or at some later time. It is |
| 50 | * therefore strongly recommended that appropriate precautions be taken to |
| 51 | * avoid the manipulation of a mapped file by this program, or by a |
| 52 | * concurrently running program, except to read or write the file's content. |
| 53 | * |
| 54 | * <p> Mapped byte buffers otherwise behave no differently than ordinary direct |
| 55 | * byte buffers. </p> |
| 56 | * |
| 57 | * |
| 58 | * @author Mark Reinhold |
| 59 | * @author JSR-51 Expert Group |
| 60 | * @since 1.4 |
| 61 | */ |
| 62 | |
| 63 | public abstract class MappedByteBuffer |
| 64 | extends ByteBuffer |
| 65 | { |
| 66 | |
| 67 | // This is a little bit backwards: By rights MappedByteBuffer should be a |
| 68 | // subclass of DirectByteBuffer, but to keep the spec clear and simple, and |
| 69 | // for optimization purposes, it's easier to do it the other way around. |
| 70 | // This works because DirectByteBuffer is a package-private class. |
| 71 | |
| 72 | // Volatile to make sure that the finalization thread sees the current |
| 73 | // value of this so that a region is not accidentally unmapped again later. |
| 74 | volatile boolean isAMappedBuffer; // package-private |
| 75 | |
| 76 | // This should only be invoked by the DirectByteBuffer constructors |
| 77 | // |
| 78 | MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private |
| 79 | boolean mapped) |
| 80 | { |
| 81 | super(mark, pos, lim, cap); |
| 82 | isAMappedBuffer = mapped; |
| 83 | } |
| 84 | |
| 85 | MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private |
| 86 | super(mark, pos, lim, cap); |
| 87 | isAMappedBuffer = false; |
| 88 | } |
| 89 | |
| 90 | private void checkMapped() { |
| 91 | if (!isAMappedBuffer) |
| 92 | // Can only happen if a luser explicitly casts a direct byte buffer |
| 93 | throw new UnsupportedOperationException(); |
| 94 | } |
| 95 | |
| 96 | /** |
| 97 | * Tells whether or not this buffer's content is resident in physical |
| 98 | * memory. |
| 99 | * |
| 100 | * <p> A return value of <tt>true</tt> implies that it is highly likely |
| 101 | * that all of the data in this buffer is resident in physical memory and |
| 102 | * may therefore be accessed without incurring any virtual-memory page |
| 103 | * faults or I/O operations. A return value of <tt>false</tt> does not |
| 104 | * necessarily imply that the buffer's content is not resident in physical |
| 105 | * memory. |
| 106 | * |
| 107 | * <p> The returned value is a hint, rather than a guarantee, because the |
| 108 | * underlying operating system may have paged out some of the buffer's data |
| 109 | * by the time that an invocation of this method returns. </p> |
| 110 | * |
| 111 | * @return <tt>true</tt> if it is likely that this buffer's content |
| 112 | * is resident in physical memory |
| 113 | */ |
| 114 | public final boolean isLoaded() { |
| 115 | checkMapped(); |
| 116 | if ((address == 0) || (capacity() == 0)) |
| 117 | return true; |
| 118 | return isLoaded0(((DirectByteBuffer)this).address(), capacity()); |
| 119 | } |
| 120 | |
| 121 | /** |
| 122 | * Loads this buffer's content into physical memory. |
| 123 | * |
| 124 | * <p> This method makes a best effort to ensure that, when it returns, |
| 125 | * this buffer's content is resident in physical memory. Invoking this |
| 126 | * method may cause some number of page faults and I/O operations to |
| 127 | * occur. </p> |
| 128 | * |
| 129 | * @return This buffer |
| 130 | */ |
| 131 | public final MappedByteBuffer load() { |
| 132 | checkMapped(); |
| 133 | if ((address == 0) || (capacity() == 0)) |
| 134 | return this; |
| 135 | load0(((DirectByteBuffer)this).address(), capacity(), Bits.pageSize()); |
| 136 | return this; |
| 137 | } |
| 138 | |
| 139 | /** |
| 140 | * Forces any changes made to this buffer's content to be written to the |
| 141 | * storage device containing the mapped file. |
| 142 | * |
| 143 | * <p> If the file mapped into this buffer resides on a local storage |
| 144 | * device then when this method returns it is guaranteed that all changes |
| 145 | * made to the buffer since it was created, or since this method was last |
| 146 | * invoked, will have been written to that device. |
| 147 | * |
| 148 | * <p> If the file does not reside on a local device then no such guarantee |
| 149 | * is made. |
| 150 | * |
| 151 | * <p> If this buffer was not mapped in read/write mode ({@link |
| 152 | * java.nio.channels.FileChannel.MapMode#READ_WRITE}) then invoking this |
| 153 | * method has no effect. </p> |
| 154 | * |
| 155 | * @return This buffer |
| 156 | */ |
| 157 | public final MappedByteBuffer force() { |
| 158 | checkMapped(); |
| 159 | if ((address == 0) || (capacity() == 0)) |
| 160 | return this; |
| 161 | force0(((DirectByteBuffer)this).address(), capacity()); |
| 162 | return this; |
| 163 | } |
| 164 | |
| 165 | private native boolean isLoaded0(long address, long length); |
| 166 | private native int load0(long address, long length, int pageSize); |
| 167 | private native void force0(long address, long length); |
| 168 | |
| 169 | } |