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| 1 | /* | ||
| 2 | * Copyright (c) 2001, 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.channels; | ||
| 27 | |||
| 28 | import java.io.IOException; | ||
| 29 | |||
| 30 | /** | ||
| 31 | * A token representing a lock on a region of a file. | ||
| 32 | * | ||
| 33 | * <p> A file-lock object is created each time a lock is acquired on a file via | ||
| 34 | * one of the {@link FileChannel#lock(long,long,boolean) lock} or {@link | ||
| 35 | * FileChannel#tryLock(long,long,boolean) tryLock} methods of the | ||
| 36 | * {@link FileChannel} class, or the {@link | ||
| 37 | * AsynchronousFileChannel#lock(long,long,boolean,Object,CompletionHandler) lock} | ||
| 38 | * or {@link AsynchronousFileChannel#tryLock(long,long,boolean) tryLock} | ||
| 39 | * methods of the {@link AsynchronousFileChannel} class. | ||
| 40 | * | ||
| 41 | * <p> A file-lock object is initially valid. It remains valid until the lock | ||
| 42 | * is released by invoking the {@link #release release} method, by closing the | ||
| 43 | * channel that was used to acquire it, or by the termination of the Java | ||
| 44 | * virtual machine, whichever comes first. The validity of a lock may be | ||
| 45 | * tested by invoking its {@link #isValid isValid} method. | ||
| 46 | * | ||
| 47 | * <p> A file lock is either <i>exclusive</i> or <i>shared</i>. A shared lock | ||
| 48 | * prevents other concurrently-running programs from acquiring an overlapping | ||
| 49 | * exclusive lock, but does allow them to acquire overlapping shared locks. An | ||
| 50 | * exclusive lock prevents other programs from acquiring an overlapping lock of | ||
| 51 | * either type. Once it is released, a lock has no further effect on the locks | ||
| 52 | * that may be acquired by other programs. | ||
| 53 | * | ||
| 54 | * <p> Whether a lock is exclusive or shared may be determined by invoking its | ||
| 55 | * {@link #isShared isShared} method. Some platforms do not support shared | ||
| 56 | * locks, in which case a request for a shared lock is automatically converted | ||
| 57 | * into a request for an exclusive lock. | ||
| 58 | * | ||
| 59 | * <p> The locks held on a particular file by a single Java virtual machine do | ||
| 60 | * not overlap. The {@link #overlaps overlaps} method may be used to test | ||
| 61 | * whether a candidate lock range overlaps an existing lock. | ||
| 62 | * | ||
| 63 | * <p> A file-lock object records the file channel upon whose file the lock is | ||
| 64 | * held, the type and validity of the lock, and the position and size of the | ||
| 65 | * locked region. Only the validity of a lock is subject to change over time; | ||
| 66 | * all other aspects of a lock's state are immutable. | ||
| 67 | * | ||
| 68 | * <p> File locks are held on behalf of the entire Java virtual machine. | ||
| 69 | * They are not suitable for controlling access to a file by multiple | ||
| 70 | * threads within the same virtual machine. | ||
| 71 | * | ||
| 72 | * <p> File-lock objects are safe for use by multiple concurrent threads. | ||
| 73 | * | ||
| 74 | * | ||
| 75 | * <a name="pdep"><h4> Platform dependencies </h4></a> | ||
| 76 | * | ||
| 77 | * <p> This file-locking API is intended to map directly to the native locking | ||
| 78 | * facility of the underlying operating system. Thus the locks held on a file | ||
| 79 | * should be visible to all programs that have access to the file, regardless | ||
| 80 | * of the language in which those programs are written. | ||
| 81 | * | ||
| 82 | * <p> Whether or not a lock actually prevents another program from accessing | ||
| 83 | * the content of the locked region is system-dependent and therefore | ||
| 84 | * unspecified. The native file-locking facilities of some systems are merely | ||
| 85 | * <i>advisory</i>, meaning that programs must cooperatively observe a known | ||
| 86 | * locking protocol in order to guarantee data integrity. On other systems | ||
| 87 | * native file locks are <i>mandatory</i>, meaning that if one program locks a | ||
| 88 | * region of a file then other programs are actually prevented from accessing | ||
| 89 | * that region in a way that would violate the lock. On yet other systems, | ||
| 90 | * whether native file locks are advisory or mandatory is configurable on a | ||
| 91 | * per-file basis. To ensure consistent and correct behavior across platforms, | ||
| 92 | * it is strongly recommended that the locks provided by this API be used as if | ||
| 93 | * they were advisory locks. | ||
| 94 | * | ||
| 95 | * <p> On some systems, acquiring a mandatory lock on a region of a file | ||
| 96 | * prevents that region from being {@link java.nio.channels.FileChannel#map | ||
| 97 | * <i>mapped into memory</i>}, and vice versa. Programs that combine | ||
| 98 | * locking and mapping should be prepared for this combination to fail. | ||
| 99 | * | ||
| 100 | * <p> On some systems, closing a channel releases all locks held by the Java | ||
| 101 | * virtual machine on the underlying file regardless of whether the locks were | ||
| 102 | * acquired via that channel or via another channel open on the same file. It | ||
| 103 | * is strongly recommended that, within a program, a unique channel be used to | ||
| 104 | * acquire all locks on any given file. | ||
| 105 | * | ||
| 106 | * <p> Some network filesystems permit file locking to be used with | ||
| 107 | * memory-mapped files only when the locked regions are page-aligned and a | ||
| 108 | * whole multiple of the underlying hardware's page size. Some network | ||
| 109 | * filesystems do not implement file locks on regions that extend past a | ||
| 110 | * certain position, often 2<sup>30</sup> or 2<sup>31</sup>. In general, great | ||
| 111 | * care should be taken when locking files that reside on network filesystems. | ||
| 112 | * | ||
| 113 | * | ||
| 114 | * @author Mark Reinhold | ||
| 115 | * @author JSR-51 Expert Group | ||
| 116 | * @since 1.4 | ||
| 117 | */ | ||
| 118 | |||
| 119 | public abstract class FileLock implements AutoCloseable { | ||
| 120 | |||
| 121 | private final Channel channel; | ||
| 122 | private final long position; | ||
| 123 | private final long size; | ||
| 124 | private final boolean shared; | ||
| 125 | |||
| 126 | /** | ||
| 127 | * Initializes a new instance of this class. </p> | ||
| 128 | * | ||
| 129 | * @param channel | ||
| 130 | * The file channel upon whose file this lock is held | ||
| 131 | * | ||
| 132 | * @param position | ||
| 133 | * The position within the file at which the locked region starts; | ||
| 134 | * must be non-negative | ||
| 135 | * | ||
| 136 | * @param size | ||
| 137 | * The size of the locked region; must be non-negative, and the sum | ||
| 138 | * <tt>position</tt> + <tt>size</tt> must be non-negative | ||
| 139 | * | ||
| 140 | * @param shared | ||
| 141 | * <tt>true</tt> if this lock is shared, | ||
| 142 | * <tt>false</tt> if it is exclusive | ||
| 143 | * | ||
| 144 | * @throws IllegalArgumentException | ||
| 145 | * If the preconditions on the parameters do not hold | ||
| 146 | */ | ||
| 147 | protected FileLock(FileChannel channel, | ||
| 148 | long position, long size, boolean shared) | ||
| 149 | { | ||
| 150 | if (position < 0) | ||
| 151 | throw new IllegalArgumentException("Negative position"); | ||
| 152 | if (size < 0) | ||
| 153 | throw new IllegalArgumentException("Negative size"); | ||
| 154 | if (position + size < 0) | ||
| 155 | throw new IllegalArgumentException("Negative position + size"); | ||
| 156 | this.channel = channel; | ||
| 157 | this.position = position; | ||
| 158 | this.size = size; | ||
| 159 | this.shared = shared; | ||
| 160 | } | ||
| 161 | |||
| 162 | /** | ||
| 163 | * Initializes a new instance of this class. | ||
| 164 | * | ||
| 165 | * @param channel | ||
| 166 | * The channel upon whose file this lock is held | ||
| 167 | * | ||
| 168 | * @param position | ||
| 169 | * The position within the file at which the locked region starts; | ||
| 170 | * must be non-negative | ||
| 171 | * | ||
| 172 | * @param size | ||
| 173 | * The size of the locked region; must be non-negative, and the sum | ||
| 174 | * <tt>position</tt> + <tt>size</tt> must be non-negative | ||
| 175 | * | ||
| 176 | * @param shared | ||
| 177 | * <tt>true</tt> if this lock is shared, | ||
| 178 | * <tt>false</tt> if it is exclusive | ||
| 179 | * | ||
| 180 | * @throws IllegalArgumentException | ||
| 181 | * If the preconditions on the parameters do not hold | ||
| 182 | * | ||
| 183 | * @since 1.7 | ||
| 184 | */ | ||
| 185 | protected FileLock(AsynchronousFileChannel channel, | ||
| 186 | long position, long size, boolean shared) | ||
| 187 | { | ||
| 188 | if (position < 0) | ||
| 189 | throw new IllegalArgumentException("Negative position"); | ||
| 190 | if (size < 0) | ||
| 191 | throw new IllegalArgumentException("Negative size"); | ||
| 192 | if (position + size < 0) | ||
| 193 | throw new IllegalArgumentException("Negative position + size"); | ||
| 194 | this.channel = channel; | ||
| 195 | this.position = position; | ||
| 196 | this.size = size; | ||
| 197 | this.shared = shared; | ||
| 198 | } | ||
| 199 | |||
| 200 | /** | ||
| 201 | * Returns the file channel upon whose file this lock was acquired. | ||
| 202 | * | ||
| 203 | * <p> This method has been superseded by the {@link #acquiredBy acquiredBy} | ||
| 204 | * method. | ||
| 205 | * | ||
| 206 | * @return The file channel, or {@code null} if the file lock was not | ||
| 207 | * acquired by a file channel. | ||
| 208 | */ | ||
| 209 | public final FileChannel channel() { | ||
| 210 | return (channel instanceof FileChannel) ? (FileChannel)channel : null; | ||
| 211 | } | ||
| 212 | |||
| 213 | /** | ||
| 214 | * Returns the channel upon whose file this lock was acquired. | ||
| 215 | * | ||
| 216 | * @return The channel upon whose file this lock was acquired. | ||
| 217 | * | ||
| 218 | * @since 1.7 | ||
| 219 | */ | ||
| 220 | public Channel acquiredBy() { | ||
| 221 | return channel; | ||
| 222 | } | ||
| 223 | |||
| 224 | /** | ||
| 225 | * Returns the position within the file of the first byte of the locked | ||
| 226 | * region. | ||
| 227 | * | ||
| 228 | * <p> A locked region need not be contained within, or even overlap, the | ||
| 229 | * actual underlying file, so the value returned by this method may exceed | ||
| 230 | * the file's current size. </p> | ||
| 231 | * | ||
| 232 | * @return The position | ||
| 233 | */ | ||
| 234 | public final long position() { | ||
| 235 | return position; | ||
| 236 | } | ||
| 237 | |||
| 238 | /** | ||
| 239 | * Returns the size of the locked region in bytes. | ||
| 240 | * | ||
| 241 | * <p> A locked region need not be contained within, or even overlap, the | ||
| 242 | * actual underlying file, so the value returned by this method may exceed | ||
| 243 | * the file's current size. </p> | ||
| 244 | * | ||
| 245 | * @return The size of the locked region | ||
| 246 | */ | ||
| 247 | public final long size() { | ||
| 248 | return size; | ||
| 249 | } | ||
| 250 | |||
| 251 | /** | ||
| 252 | * Tells whether this lock is shared. </p> | ||
| 253 | * | ||
| 254 | * @return <tt>true</tt> if lock is shared, | ||
| 255 | * <tt>false</tt> if it is exclusive | ||
| 256 | */ | ||
| 257 | public final boolean isShared() { | ||
| 258 | return shared; | ||
| 259 | } | ||
| 260 | |||
| 261 | /** | ||
| 262 | * Tells whether or not this lock overlaps the given lock range. </p> | ||
| 263 | * | ||
| 264 | * @return <tt>true</tt> if, and only if, this lock and the given lock | ||
| 265 | * range overlap by at least one byte | ||
| 266 | */ | ||
| 267 | public final boolean overlaps(long position, long size) { | ||
| 268 | if (position + size <= this.position) | ||
| 269 | return false; // That is below this | ||
| 270 | if (this.position + this.size <= position) | ||
| 271 | return false; // This is below that | ||
| 272 | return true; | ||
| 273 | } | ||
| 274 | |||
| 275 | /** | ||
| 276 | * Tells whether or not this lock is valid. | ||
| 277 | * | ||
| 278 | * <p> A lock object remains valid until it is released or the associated | ||
| 279 | * file channel is closed, whichever comes first. </p> | ||
| 280 | * | ||
| 281 | * @return <tt>true</tt> if, and only if, this lock is valid | ||
| 282 | */ | ||
| 283 | public abstract boolean isValid(); | ||
| 284 | |||
| 285 | /** | ||
| 286 | * Releases this lock. | ||
| 287 | * | ||
| 288 | * <p> If this lock object is valid then invoking this method releases the | ||
| 289 | * lock and renders the object invalid. If this lock object is invalid | ||
| 290 | * then invoking this method has no effect. </p> | ||
| 291 | * | ||
| 292 | * @throws ClosedChannelException | ||
| 293 | * If the channel that was used to acquire this lock | ||
| 294 | * is no longer open | ||
| 295 | * | ||
| 296 | * @throws IOException | ||
| 297 | * If an I/O error occurs | ||
| 298 | */ | ||
| 299 | public abstract void release() throws IOException; | ||
| 300 | |||
| 301 | /** | ||
| 302 | * This method invokes the {@link #release} method. It was added | ||
| 303 | * to the class so that it could be used in conjunction with the | ||
| 304 | * automatic resource management block construct. | ||
| 305 | * | ||
| 306 | * @since 1.7 | ||
| 307 | */ | ||
| 308 | public final void close() throws IOException { | ||
| 309 | release(); | ||
| 310 | } | ||
| 311 | |||
| 312 | /** | ||
| 313 | * Returns a string describing the range, type, and validity of this lock. | ||
| 314 | * | ||
| 315 | * @return A descriptive string | ||
| 316 | */ | ||
| 317 | public final String toString() { | ||
| 318 | return (this.getClass().getName() | ||
| 319 | + "[" + position | ||
| 320 | + ":" + size | ||
| 321 | + " " + (shared ? "shared" : "exclusive") | ||
| 322 | + " " + (isValid() ? "valid" : "invalid") | ||
| 323 | + "]"); | ||
| 324 | } | ||
| 325 | |||
| 326 | } | ||