1 /* 2 * Copyright (c) 2007, 2011, 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.nio.file.*; 29 import java.nio.file.attribute.FileAttribute; 30 import java.nio.file.spi.*; 31 import java.nio.ByteBuffer; 32 import java.io.IOException; 33 import java.util.concurrent.Future; 34 import java.util.concurrent.ExecutorService; 35 import java.util.Set; 36 import java.util.HashSet; 37 import java.util.Collections; 38 39 /** 40 * An asynchronous channel for reading, writing, and manipulating a file. 41 * 42 * <p> An asynchronous file channel is created when a file is opened by invoking 43 * one of the {@link #open open} methods defined by this class. The file contains 44 * a variable-length sequence of bytes that can be read and written and whose 45 * current size can be {@link #size() queried}. The size of the file increases 46 * when bytes are written beyond its current size; the size of the file decreases 47 * when it is {@link #truncate truncated}. 48 * 49 * <p> An asynchronous file channel does not have a <i>current position</i> 50 * within the file. Instead, the file position is specified to each read and 51 * write method that initiates asynchronous operations. A {@link CompletionHandler} 52 * is specified as a parameter and is invoked to consume the result of the I/O 53 * operation. This class also defines read and write methods that initiate 54 * asynchronous operations, returning a {@link Future} to represent the pending 55 * result of the operation. The {@code Future} may be used to check if the 56 * operation has completed, wait for its completion, and retrieve the result. 57 * 58 * <p> In addition to read and write operations, this class defines the 59 * following operations: </p> 60 * 61 * <ul> 62 * 63 * <li><p> Updates made to a file may be {@link #force <i>forced 64 * out</i>} to the underlying storage device, ensuring that data are not 65 * lost in the event of a system crash. </p></li> 66 * 67 * <li><p> A region of a file may be {@link #lock <i>locked</i>} against 68 * access by other programs. </p></li> 69 * 70 * </ul> 71 * 72 * <p> An {@code AsynchronousFileChannel} is associated with a thread pool to 73 * which tasks are submitted to handle I/O events and dispatch to completion 74 * handlers that consume the results of I/O operations on the channel. The 75 * completion handler for an I/O operation initiated on a channel is guaranteed 76 * to be invoked by one of the threads in the thread pool (This ensures that the 77 * completion handler is run by a thread with the expected <em>identity</em>). 78 * Where an I/O operation completes immediately, and the initiating thread is 79 * itself a thread in the thread pool, then the completion handler may be invoked 80 * directly by the initiating thread. When an {@code AsynchronousFileChannel} is 81 * created without specifying a thread pool then the channel is associated with 82 * a system-dependent default thread pool that may be shared with other 83 * channels. The default thread pool is configured by the system properties 84 * defined by the {@link AsynchronousChannelGroup} class. 85 * 86 * <p> Channels of this type are safe for use by multiple concurrent threads. The 87 * {@link Channel#close close} method may be invoked at any time, as specified 88 * by the {@link Channel} interface. This causes all outstanding asynchronous 89 * operations on the channel to complete with the exception {@link 90 * AsynchronousCloseException}. Multiple read and write operations may be 91 * outstanding at the same time. When multiple read and write operations are 92 * outstanding then the ordering of the I/O operations, and the order that the 93 * completion handlers are invoked, is not specified; they are not, in particular, 94 * guaranteed to execute in the order that the operations were initiated. The 95 * {@link java.nio.ByteBuffer ByteBuffers} used when reading or writing are not 96 * safe for use by multiple concurrent I/O operations. Furthermore, after an I/O 97 * operation is initiated then care should be taken to ensure that the buffer is 98 * not accessed until after the operation has completed. 99 * 100 * <p> As with {@link FileChannel}, the view of a file provided by an instance of 101 * this class is guaranteed to be consistent with other views of the same file 102 * provided by other instances in the same program. The view provided by an 103 * instance of this class may or may not, however, be consistent with the views 104 * seen by other concurrently-running programs due to caching performed by the 105 * underlying operating system and delays induced by network-filesystem protocols. 106 * This is true regardless of the language in which these other programs are 107 * written, and whether they are running on the same machine or on some other 108 * machine. The exact nature of any such inconsistencies are system-dependent 109 * and are therefore unspecified. 110 * 111 * @since 1.7 112 */ 113 114 public abstract class AsynchronousFileChannel 115 implements AsynchronousChannel 116 { 117 /** 118 * Initializes a new instance of this class. 119 */ 120 protected AsynchronousFileChannel() { 121 } 122 123 /** 124 * Opens or creates a file for reading and/or writing, returning an 125 * asynchronous file channel to access the file. 126 * 127 * <p> The {@code options} parameter determines how the file is opened. 128 * The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE 129 * WRITE} options determines if the file should be opened for reading and/or 130 * writing. If neither option is contained in the array then an existing file 131 * is opened for reading. 132 * 133 * <p> In addition to {@code READ} and {@code WRITE}, the following options 134 * may be present: 135 * 136 * <table border=1 cellpadding=5 summary=""> 137 * <tr> <th>Option</th> <th>Description</th> </tr> 138 * <tr> 139 * <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td> 140 * <td> When opening an existing file, the file is first truncated to a 141 * size of 0 bytes. This option is ignored when the file is opened only 142 * for reading.</td> 143 * </tr> 144 * <tr> 145 * <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td> 146 * <td> If this option is present then a new file is created, failing if 147 * the file already exists. When creating a file the check for the 148 * existence of the file and the creation of the file if it does not exist 149 * is atomic with respect to other file system operations. This option is 150 * ignored when the file is opened only for reading. </td> 151 * </tr> 152 * <tr> 153 * <td > {@link StandardOpenOption#CREATE CREATE} </td> 154 * <td> If this option is present then an existing file is opened if it 155 * exists, otherwise a new file is created. When creating a file the check 156 * for the existence of the file and the creation of the file if it does 157 * not exist is atomic with respect to other file system operations. This 158 * option is ignored if the {@code CREATE_NEW} option is also present or 159 * the file is opened only for reading. </td> 160 * </tr> 161 * <tr> 162 * <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td> 163 * <td> When this option is present then the implementation makes a 164 * <em>best effort</em> attempt to delete the file when closed by the 165 * the {@link #close close} method. If the {@code close} method is not 166 * invoked then a <em>best effort</em> attempt is made to delete the file 167 * when the Java virtual machine terminates. </td> 168 * </tr> 169 * <tr> 170 * <td>{@link StandardOpenOption#SPARSE SPARSE} </td> 171 * <td> When creating a new file this option is a <em>hint</em> that the 172 * new file will be sparse. This option is ignored when not creating 173 * a new file. </td> 174 * </tr> 175 * <tr> 176 * <td> {@link StandardOpenOption#SYNC SYNC} </td> 177 * <td> Requires that every update to the file's content or metadata be 178 * written synchronously to the underlying storage device. (see <a 179 * href="../file/package-summary.html#integrity"> Synchronized I/O file 180 * integrity</a>). </td> 181 * <tr> 182 * <tr> 183 * <td> {@link StandardOpenOption#DSYNC DSYNC} </td> 184 * <td> Requires that every update to the file's content be written 185 * synchronously to the underlying storage device. (see <a 186 * href="../file/package-summary.html#integrity"> Synchronized I/O file 187 * integrity</a>). </td> 188 * </tr> 189 * </table> 190 * 191 * <p> An implementation may also support additional options. 192 * 193 * <p> The {@code executor} parameter is the {@link ExecutorService} to 194 * which tasks are submitted to handle I/O events and dispatch completion 195 * results for operations initiated on resulting channel. 196 * The nature of these tasks is highly implementation specific and so care 197 * should be taken when configuring the {@code Executor}. Minimally it 198 * should support an unbounded work queue and should not run tasks on the 199 * caller thread of the {@link ExecutorService#execute execute} method. 200 * Shutting down the executor service while the channel is open results in 201 * unspecified behavior. 202 * 203 * <p> The {@code attrs} parameter is an optional array of file {@link 204 * FileAttribute file-attributes} to set atomically when creating the file. 205 * 206 * <p> The new channel is created by invoking the {@link 207 * FileSystemProvider#newFileChannel newFileChannel} method on the 208 * provider that created the {@code Path}. 209 * 210 * @param file 211 * The path of the file to open or create 212 * @param options 213 * Options specifying how the file is opened 214 * @param executor 215 * The thread pool or {@code null} to associate the channel with 216 * the default thread pool 217 * @param attrs 218 * An optional list of file attributes to set atomically when 219 * creating the file 220 * 221 * @return A new asynchronous file channel 222 * 223 * @throws IllegalArgumentException 224 * If the set contains an invalid combination of options 225 * @throws UnsupportedOperationException 226 * If the {@code file} is associated with a provider that does not 227 * support creating asynchronous file channels, or an unsupported 228 * open option is specified, or the array contains an attribute that 229 * cannot be set atomically when creating the file 230 * @throws IOException 231 * If an I/O error occurs 232 * @throws SecurityException 233 * If a security manager is installed and it denies an 234 * unspecified permission required by the implementation. 235 * In the case of the default provider, the {@link 236 * SecurityManager#checkRead(String)} method is invoked to check 237 * read access if the file is opened for reading. The {@link 238 * SecurityManager#checkWrite(String)} method is invoked to check 239 * write access if the file is opened for writing 240 */ 241 public static AsynchronousFileChannel open(Path file, 242 Set<? extends OpenOption> options, 243 ExecutorService executor, 244 FileAttribute<?>... attrs) 245 throws IOException 246 { 247 FileSystemProvider provider = file.getFileSystem().provider(); 248 return provider.newAsynchronousFileChannel(file, options, executor, attrs); 249 } 250 251 @SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction 252 private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0]; 253 254 /** 255 * Opens or creates a file for reading and/or writing, returning an 256 * asynchronous file channel to access the file. 257 * 258 * <p> An invocation of this method behaves in exactly the same way as the 259 * invocation 260 * <pre> 261 * ch.{@link #open(Path,Set,ExecutorService,FileAttribute[]) 262 * open}(file, opts, null, new FileAttribute<?>[0]); 263 * </pre> 264 * where {@code opts} is a {@code Set} containing the options specified to 265 * this method. 266 * 267 * <p> The resulting channel is associated with default thread pool to which 268 * tasks are submitted to handle I/O events and dispatch to completion 269 * handlers that consume the result of asynchronous operations performed on 270 * the resulting channel. 271 * 272 * @param file 273 * The path of the file to open or create 274 * @param options 275 * Options specifying how the file is opened 276 * 277 * @return A new asynchronous file channel 278 * 279 * @throws IllegalArgumentException 280 * If the set contains an invalid combination of options 281 * @throws UnsupportedOperationException 282 * If the {@code file} is associated with a provider that does not 283 * support creating file channels, or an unsupported open option is 284 * specified 285 * @throws IOException 286 * If an I/O error occurs 287 * @throws SecurityException 288 * If a security manager is installed and it denies an 289 * unspecified permission required by the implementation. 290 * In the case of the default provider, the {@link 291 * SecurityManager#checkRead(String)} method is invoked to check 292 * read access if the file is opened for reading. The {@link 293 * SecurityManager#checkWrite(String)} method is invoked to check 294 * write access if the file is opened for writing 295 */ 296 public static AsynchronousFileChannel open(Path file, OpenOption... options) 297 throws IOException 298 { 299 Set<OpenOption> set = new HashSet<OpenOption>(options.length); 300 Collections.addAll(set, options); 301 return open(file, set, null, NO_ATTRIBUTES); 302 } 303 304 /** 305 * Returns the current size of this channel's file. 306 * 307 * @return The current size of this channel's file, measured in bytes 308 * 309 * @throws ClosedChannelException 310 * If this channel is closed 311 * @throws IOException 312 * If some other I/O error occurs 313 */ 314 public abstract long size() throws IOException; 315 316 /** 317 * Truncates this channel's file to the given size. 318 * 319 * <p> If the given size is less than the file's current size then the file 320 * is truncated, discarding any bytes beyond the new end of the file. If 321 * the given size is greater than or equal to the file's current size then 322 * the file is not modified. </p> 323 * 324 * @param size 325 * The new size, a non-negative byte count 326 * 327 * @return This file channel 328 * 329 * @throws NonWritableChannelException 330 * If this channel was not opened for writing 331 * 332 * @throws ClosedChannelException 333 * If this channel is closed 334 * 335 * @throws IllegalArgumentException 336 * If the new size is negative 337 * 338 * @throws IOException 339 * If some other I/O error occurs 340 */ 341 public abstract AsynchronousFileChannel truncate(long size) throws IOException; 342 343 /** 344 * Forces any updates to this channel's file to be written to the storage 345 * device that contains it. 346 * 347 * <p> If this channel's file resides on a local storage device then when 348 * this method returns it is guaranteed that all changes made to the file 349 * since this channel was created, or since this method was last invoked, 350 * will have been written to that device. This is useful for ensuring that 351 * critical information is not lost in the event of a system crash. 352 * 353 * <p> If the file does not reside on a local device then no such guarantee 354 * is made. 355 * 356 * <p> The {@code metaData} parameter can be used to limit the number of 357 * I/O operations that this method is required to perform. Passing 358 * {@code false} for this parameter indicates that only updates to the 359 * file's content need be written to storage; passing {@code true} 360 * indicates that updates to both the file's content and metadata must be 361 * written, which generally requires at least one more I/O operation. 362 * Whether this parameter actually has any effect is dependent upon the 363 * underlying operating system and is therefore unspecified. 364 * 365 * <p> Invoking this method may cause an I/O operation to occur even if the 366 * channel was only opened for reading. Some operating systems, for 367 * example, maintain a last-access time as part of a file's metadata, and 368 * this time is updated whenever the file is read. Whether or not this is 369 * actually done is system-dependent and is therefore unspecified. 370 * 371 * <p> This method is only guaranteed to force changes that were made to 372 * this channel's file via the methods defined in this class. 373 * 374 * @param metaData 375 * If {@code true} then this method is required to force changes 376 * to both the file's content and metadata to be written to 377 * storage; otherwise, it need only force content changes to be 378 * written 379 * 380 * @throws ClosedChannelException 381 * If this channel is closed 382 * 383 * @throws IOException 384 * If some other I/O error occurs 385 */ 386 public abstract void force(boolean metaData) throws IOException; 387 388 /** 389 * Acquires a lock on the given region of this channel's file. 390 * 391 * <p> This method initiates an operation to acquire a lock on the given 392 * region of this channel's file. The {@code handler} parameter is a 393 * completion handler that is invoked when the lock is acquired (or the 394 * operation fails). The result passed to the completion handler is the 395 * resulting {@code FileLock}. 396 * 397 * <p> The region specified by the {@code position} and {@code size} 398 * parameters need not be contained within, or even overlap, the actual 399 * underlying file. Lock regions are fixed in size; if a locked region 400 * initially contains the end of the file and the file grows beyond the 401 * region then the new portion of the file will not be covered by the lock. 402 * If a file is expected to grow in size and a lock on the entire file is 403 * required then a region starting at zero, and no smaller than the 404 * expected maximum size of the file, should be locked. The two-argument 405 * {@link #lock(Object,CompletionHandler)} method simply locks a region 406 * of size {@link Long#MAX_VALUE}. If a lock that overlaps the requested 407 * region is already held by this Java virtual machine, or this method has 408 * been invoked to lock an overlapping region and that operation has not 409 * completed, then this method throws {@link OverlappingFileLockException}. 410 * 411 * <p> Some operating systems do not support a mechanism to acquire a file 412 * lock in an asynchronous manner. Consequently an implementation may 413 * acquire the file lock in a background thread or from a task executed by 414 * a thread in the associated thread pool. If there are many lock operations 415 * outstanding then it may consume threads in the Java virtual machine for 416 * indefinite periods. 417 * 418 * <p> Some operating systems do not support shared locks, in which case a 419 * request for a shared lock is automatically converted into a request for 420 * an exclusive lock. Whether the newly-acquired lock is shared or 421 * exclusive may be tested by invoking the resulting lock object's {@link 422 * FileLock#isShared() isShared} method. 423 * 424 * <p> File locks are held on behalf of the entire Java virtual machine. 425 * They are not suitable for controlling access to a file by multiple 426 * threads within the same virtual machine. 427 * 428 * @param position 429 * The position at which the locked region is to start; must be 430 * non-negative 431 * @param size 432 * The size of the locked region; must be non-negative, and the sum 433 * {@code position} + {@code size} must be non-negative 434 * @param shared 435 * {@code true} to request a shared lock, in which case this 436 * channel must be open for reading (and possibly writing); 437 * {@code false} to request an exclusive lock, in which case this 438 * channel must be open for writing (and possibly reading) 439 * @param attachment 440 * The object to attach to the I/O operation; can be {@code null} 441 * @param handler 442 * The handler for consuming the result 443 * 444 * @throws OverlappingFileLockException 445 * If a lock that overlaps the requested region is already held by 446 * this Java virtual machine, or there is already a pending attempt 447 * to lock an overlapping region 448 * @throws IllegalArgumentException 449 * If the preconditions on the parameters do not hold 450 * @throws NonReadableChannelException 451 * If {@code shared} is true but this channel was not opened for reading 452 * @throws NonWritableChannelException 453 * If {@code shared} is false but this channel was not opened for writing 454 */ 455 public abstract <A> void lock(long position, 456 long size, 457 boolean shared, 458 A attachment, 459 CompletionHandler<FileLock,? super A> handler); 460 461 /** 462 * Acquires an exclusive lock on this channel's file. 463 * 464 * <p> This method initiates an operation to acquire a lock on the given 465 * region of this channel's file. The {@code handler} parameter is a 466 * completion handler that is invoked when the lock is acquired (or the 467 * operation fails). The result passed to the completion handler is the 468 * resulting {@code FileLock}. 469 * 470 * <p> An invocation of this method of the form {@code ch.lock(att,handler)} 471 * behaves in exactly the same way as the invocation 472 * <pre> 473 * ch.{@link #lock(long,long,boolean,Object,CompletionHandler) lock}(0L, Long.MAX_VALUE, false, att, handler) 474 * </pre> 475 * 476 * @param attachment 477 * The object to attach to the I/O operation; can be {@code null} 478 * @param handler 479 * The handler for consuming the result 480 * 481 * @throws OverlappingFileLockException 482 * If a lock is already held by this Java virtual machine, or there 483 * is already a pending attempt to lock a region 484 * @throws NonWritableChannelException 485 * If this channel was not opened for writing 486 */ 487 public final <A> void lock(A attachment, 488 CompletionHandler<FileLock,? super A> handler) 489 { 490 lock(0L, Long.MAX_VALUE, false, attachment, handler); 491 } 492 493 /** 494 * Acquires a lock on the given region of this channel's file. 495 * 496 * <p> This method initiates an operation to acquire a lock on the given 497 * region of this channel's file. The method behaves in exactly the same 498 * manner as the {@link #lock(long, long, boolean, Object, CompletionHandler)} 499 * method except that instead of specifying a completion handler, this 500 * method returns a {@code Future} representing the pending result. The 501 * {@code Future}'s {@link Future#get() get} method returns the {@link 502 * FileLock} on successful completion. 503 * 504 * @param position 505 * The position at which the locked region is to start; must be 506 * non-negative 507 * @param size 508 * The size of the locked region; must be non-negative, and the sum 509 * {@code position} + {@code size} must be non-negative 510 * @param shared 511 * {@code true} to request a shared lock, in which case this 512 * channel must be open for reading (and possibly writing); 513 * {@code false} to request an exclusive lock, in which case this 514 * channel must be open for writing (and possibly reading) 515 * 516 * @return a {@code Future} object representing the pending result 517 * 518 * @throws OverlappingFileLockException 519 * If a lock is already held by this Java virtual machine, or there 520 * is already a pending attempt to lock a region 521 * @throws IllegalArgumentException 522 * If the preconditions on the parameters do not hold 523 * @throws NonReadableChannelException 524 * If {@code shared} is true but this channel was not opened for reading 525 * @throws NonWritableChannelException 526 * If {@code shared} is false but this channel was not opened for writing 527 */ 528 public abstract Future<FileLock> lock(long position, long size, boolean shared); 529 530 /** 531 * Acquires an exclusive lock on this channel's file. 532 * 533 * <p> This method initiates an operation to acquire an exclusive lock on this 534 * channel's file. The method returns a {@code Future} representing the 535 * pending result of the operation. The {@code Future}'s {@link Future#get() 536 * get} method returns the {@link FileLock} on successful completion. 537 * 538 * <p> An invocation of this method behaves in exactly the same way as the 539 * invocation 540 * <pre> 541 * ch.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) 542 * </pre> 543 * 544 * @return a {@code Future} object representing the pending result 545 * 546 * @throws OverlappingFileLockException 547 * If a lock is already held by this Java virtual machine, or there 548 * is already a pending attempt to lock a region 549 * @throws NonWritableChannelException 550 * If this channel was not opened for writing 551 */ 552 public final Future<FileLock> lock() { 553 return lock(0L, Long.MAX_VALUE, false); 554 } 555 556 /** 557 * Attempts to acquire a lock on the given region of this channel's file. 558 * 559 * <p> This method does not block. An invocation always returns immediately, 560 * either having acquired a lock on the requested region or having failed to 561 * do so. If it fails to acquire a lock because an overlapping lock is held 562 * by another program then it returns {@code null}. If it fails to acquire 563 * a lock for any other reason then an appropriate exception is thrown. 564 * 565 * @param position 566 * The position at which the locked region is to start; must be 567 * non-negative 568 * 569 * @param size 570 * The size of the locked region; must be non-negative, and the sum 571 * {@code position} + {@code size} must be non-negative 572 * 573 * @param shared 574 * {@code true} to request a shared lock, 575 * {@code false} to request an exclusive lock 576 * 577 * @return A lock object representing the newly-acquired lock, 578 * or {@code null} if the lock could not be acquired 579 * because another program holds an overlapping lock 580 * 581 * @throws IllegalArgumentException 582 * If the preconditions on the parameters do not hold 583 * @throws ClosedChannelException 584 * If this channel is closed 585 * @throws OverlappingFileLockException 586 * If a lock that overlaps the requested region is already held by 587 * this Java virtual machine, or if another thread is already 588 * blocked in this method and is attempting to lock an overlapping 589 * region of the same file 590 * @throws NonReadableChannelException 591 * If {@code shared} is true but this channel was not opened for reading 592 * @throws NonWritableChannelException 593 * If {@code shared} is false but this channel was not opened for writing 594 * 595 * @throws IOException 596 * If some other I/O error occurs 597 * 598 * @see #lock(Object,CompletionHandler) 599 * @see #lock(long,long,boolean,Object,CompletionHandler) 600 * @see #tryLock() 601 */ 602 public abstract FileLock tryLock(long position, long size, boolean shared) 603 throws IOException; 604 605 /** 606 * Attempts to acquire an exclusive lock on this channel's file. 607 * 608 * <p> An invocation of this method of the form {@code ch.tryLock()} 609 * behaves in exactly the same way as the invocation 610 * 611 * <pre> 612 * ch.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre> 613 * 614 * @return A lock object representing the newly-acquired lock, 615 * or {@code null} if the lock could not be acquired 616 * because another program holds an overlapping lock 617 * 618 * @throws ClosedChannelException 619 * If this channel is closed 620 * @throws OverlappingFileLockException 621 * If a lock that overlaps the requested region is already held by 622 * this Java virtual machine, or if another thread is already 623 * blocked in this method and is attempting to lock an overlapping 624 * region 625 * @throws NonWritableChannelException 626 * If {@code shared} is false but this channel was not opened for writing 627 * 628 * @throws IOException 629 * If some other I/O error occurs 630 * 631 * @see #lock(Object,CompletionHandler) 632 * @see #lock(long,long,boolean,Object,CompletionHandler) 633 * @see #tryLock(long,long,boolean) 634 */ 635 public final FileLock tryLock() throws IOException { 636 return tryLock(0L, Long.MAX_VALUE, false); 637 } 638 639 /** 640 * Reads a sequence of bytes from this channel into the given buffer, 641 * starting at the given file position. 642 * 643 * <p> This method initiates the reading of a sequence of bytes from this 644 * channel into the given buffer, starting at the given file position. The 645 * result of the read is the number of bytes read or {@code -1} if the given 646 * position is greater than or equal to the file's size at the time that the 647 * read is attempted. 648 * 649 * <p> This method works in the same manner as the {@link 650 * AsynchronousByteChannel#read(ByteBuffer,Object,CompletionHandler)} 651 * method, except that bytes are read starting at the given file position. 652 * If the given file position is greater than the file's size at the time 653 * that the read is attempted then no bytes are read. 654 * 655 * @param dst 656 * The buffer into which bytes are to be transferred 657 * @param position 658 * The file position at which the transfer is to begin; 659 * must be non-negative 660 * @param attachment 661 * The object to attach to the I/O operation; can be {@code null} 662 * @param handler 663 * The handler for consuming the result 664 * 665 * @throws IllegalArgumentException 666 * If the position is negative or the buffer is read-only 667 * @throws NonReadableChannelException 668 * If this channel was not opened for reading 669 */ 670 public abstract <A> void read(ByteBuffer dst, 671 long position, 672 A attachment, 673 CompletionHandler<Integer,? super A> handler); 674 675 /** 676 * Reads a sequence of bytes from this channel into the given buffer, 677 * starting at the given file position. 678 * 679 * <p> This method initiates the reading of a sequence of bytes from this 680 * channel into the given buffer, starting at the given file position. This 681 * method returns a {@code Future} representing the pending result of the 682 * operation. The {@code Future}'s {@link Future#get() get} method returns 683 * the number of bytes read or {@code -1} if the given position is greater 684 * than or equal to the file's size at the time that the read is attempted. 685 * 686 * <p> This method works in the same manner as the {@link 687 * AsynchronousByteChannel#read(ByteBuffer)} method, except that bytes are 688 * read starting at the given file position. If the given file position is 689 * greater than the file's size at the time that the read is attempted then 690 * no bytes are read. 691 * 692 * @param dst 693 * The buffer into which bytes are to be transferred 694 * @param position 695 * The file position at which the transfer is to begin; 696 * must be non-negative 697 * 698 * @return A {@code Future} object representing the pending result 699 * 700 * @throws IllegalArgumentException 701 * If the position is negative or the buffer is read-only 702 * @throws NonReadableChannelException 703 * If this channel was not opened for reading 704 */ 705 public abstract Future<Integer> read(ByteBuffer dst, long position); 706 707 /** 708 * Writes a sequence of bytes to this channel from the given buffer, starting 709 * at the given file position. 710 * 711 * <p> This method works in the same manner as the {@link 712 * AsynchronousByteChannel#write(ByteBuffer,Object,CompletionHandler)} 713 * method, except that bytes are written starting at the given file position. 714 * If the given position is greater than the file's size, at the time that 715 * the write is attempted, then the file will be grown to accommodate the new 716 * bytes; the values of any bytes between the previous end-of-file and the 717 * newly-written bytes are unspecified. 718 * 719 * @param src 720 * The buffer from which bytes are to be transferred 721 * @param position 722 * The file position at which the transfer is to begin; 723 * must be non-negative 724 * @param attachment 725 * The object to attach to the I/O operation; can be {@code null} 726 * @param handler 727 * The handler for consuming the result 728 * 729 * @throws IllegalArgumentException 730 * If the position is negative 731 * @throws NonWritableChannelException 732 * If this channel was not opened for writing 733 */ 734 public abstract <A> void write(ByteBuffer src, 735 long position, 736 A attachment, 737 CompletionHandler<Integer,? super A> handler); 738 739 /** 740 * Writes a sequence of bytes to this channel from the given buffer, starting 741 * at the given file position. 742 * 743 * <p> This method initiates the writing of a sequence of bytes to this 744 * channel from the given buffer, starting at the given file position. The 745 * method returns a {@code Future} representing the pending result of the 746 * write operation. The {@code Future}'s {@link Future#get() get} method 747 * returns the number of bytes written. 748 * 749 * <p> This method works in the same manner as the {@link 750 * AsynchronousByteChannel#write(ByteBuffer)} method, except that bytes are 751 * written starting at the given file position. If the given position is 752 * greater than the file's size, at the time that the write is attempted, 753 * then the file will be grown to accommodate the new bytes; the values of 754 * any bytes between the previous end-of-file and the newly-written bytes 755 * are unspecified. 756 * 757 * @param src 758 * The buffer from which bytes are to be transferred 759 * @param position 760 * The file position at which the transfer is to begin; 761 * must be non-negative 762 * 763 * @return A {@code Future} object representing the pending result 764 * 765 * @throws IllegalArgumentException 766 * If the position is negative 767 * @throws NonWritableChannelException 768 * If this channel was not opened for writing 769 */ 770 public abstract Future<Integer> write(ByteBuffer src, long position); 771 }