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 private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0]; 252 253 /** 254 * Opens or creates a file for reading and/or writing, returning an 255 * asynchronous file channel to access the file. 256 * 257 * <p> An invocation of this method behaves in exactly the same way as the 258 * invocation 259 * <pre> 260 * ch.{@link #open(Path,Set,ExecutorService,FileAttribute[]) 261 * open}(file, opts, null, new FileAttribute<?>[0]); 262 * </pre> 263 * where {@code opts} is a {@code Set} containing the options specified to 264 * this method. 265 * 266 * <p> The resulting channel is associated with default thread pool to which 267 * tasks are submitted to handle I/O events and dispatch to completion 268 * handlers that consume the result of asynchronous operations performed on 269 * the resulting channel. 270 * 271 * @param file 272 * The path of the file to open or create 273 * @param options 274 * Options specifying how the file is opened 275 * 276 * @return A new asynchronous file channel 277 * 278 * @throws IllegalArgumentException 279 * If the set contains an invalid combination of options 280 * @throws UnsupportedOperationException 281 * If the {@code file} is associated with a provider that does not 282 * support creating file channels, or an unsupported open option is 283 * specified 284 * @throws IOException 285 * If an I/O error occurs 286 * @throws SecurityException 287 * If a security manager is installed and it denies an 288 * unspecified permission required by the implementation. 289 * In the case of the default provider, the {@link 290 * SecurityManager#checkRead(String)} method is invoked to check 291 * read access if the file is opened for reading. The {@link 292 * SecurityManager#checkWrite(String)} method is invoked to check 293 * write access if the file is opened for writing 294 */ 295 public static AsynchronousFileChannel open(Path file, OpenOption... options) 296 throws IOException 297 { 298 Set<OpenOption> set = new HashSet<OpenOption>(options.length); 299 Collections.addAll(set, options); 300 return open(file, set, null, NO_ATTRIBUTES); 301 } 302 303 /** 304 * Returns the current size of this channel's file. 305 * 306 * @return The current size of this channel's file, measured in bytes 307 * 308 * @throws ClosedChannelException 309 * If this channel is closed 310 * @throws IOException 311 * If some other I/O error occurs 312 */ 313 public abstract long size() throws IOException; 314 315 /** 316 * Truncates this channel's file to the given size. 317 * 318 * <p> If the given size is less than the file's current size then the file 319 * is truncated, discarding any bytes beyond the new end of the file. If 320 * the given size is greater than or equal to the file's current size then 321 * the file is not modified. </p> 322 * 323 * @param size 324 * The new size, a non-negative byte count 325 * 326 * @return This file channel 327 * 328 * @throws NonWritableChannelException 329 * If this channel was not opened for writing 330 * 331 * @throws ClosedChannelException 332 * If this channel is closed 333 * 334 * @throws IllegalArgumentException 335 * If the new size is negative 336 * 337 * @throws IOException 338 * If some other I/O error occurs 339 */ 340 public abstract AsynchronousFileChannel truncate(long size) throws IOException; 341 342 /** 343 * Forces any updates to this channel's file to be written to the storage 344 * device that contains it. 345 * 346 * <p> If this channel's file resides on a local storage device then when 347 * this method returns it is guaranteed that all changes made to the file 348 * since this channel was created, or since this method was last invoked, 349 * will have been written to that device. This is useful for ensuring that 350 * critical information is not lost in the event of a system crash. 351 * 352 * <p> If the file does not reside on a local device then no such guarantee 353 * is made. 354 * 355 * <p> The {@code metaData} parameter can be used to limit the number of 356 * I/O operations that this method is required to perform. Passing 357 * {@code false} for this parameter indicates that only updates to the 358 * file's content need be written to storage; passing {@code true} 359 * indicates that updates to both the file's content and metadata must be 360 * written, which generally requires at least one more I/O operation. 361 * Whether this parameter actually has any effect is dependent upon the 362 * underlying operating system and is therefore unspecified. 363 * 364 * <p> Invoking this method may cause an I/O operation to occur even if the 365 * channel was only opened for reading. Some operating systems, for 366 * example, maintain a last-access time as part of a file's metadata, and 367 * this time is updated whenever the file is read. Whether or not this is 368 * actually done is system-dependent and is therefore unspecified. 369 * 370 * <p> This method is only guaranteed to force changes that were made to 371 * this channel's file via the methods defined in this class. 372 * 373 * @param metaData 374 * If {@code true} then this method is required to force changes 375 * to both the file's content and metadata to be written to 376 * storage; otherwise, it need only force content changes to be 377 * written 378 * 379 * @throws ClosedChannelException 380 * If this channel is closed 381 * 382 * @throws IOException 383 * If some other I/O error occurs 384 */ 385 public abstract void force(boolean metaData) throws IOException; 386 387 /** 388 * Acquires a lock on the given region of this channel's file. 389 * 390 * <p> This method initiates an operation to acquire a lock on the given 391 * region of this channel's file. The {@code handler} parameter is a 392 * completion handler that is invoked when the lock is acquired (or the 393 * operation fails). The result passed to the completion handler is the 394 * resulting {@code FileLock}. 395 * 396 * <p> The region specified by the {@code position} and {@code size} 397 * parameters need not be contained within, or even overlap, the actual 398 * underlying file. Lock regions are fixed in size; if a locked region 399 * initially contains the end of the file and the file grows beyond the 400 * region then the new portion of the file will not be covered by the lock. 401 * If a file is expected to grow in size and a lock on the entire file is 402 * required then a region starting at zero, and no smaller than the 403 * expected maximum size of the file, should be locked. The two-argument 404 * {@link #lock(Object,CompletionHandler)} method simply locks a region 405 * of size {@link Long#MAX_VALUE}. If a lock that overlaps the requested 406 * region is already held by this Java virtual machine, or this method has 407 * been invoked to lock an overlapping region and that operation has not 408 * completed, then this method throws {@link OverlappingFileLockException}. 409 * 410 * <p> Some operating systems do not support a mechanism to acquire a file 411 * lock in an asynchronous manner. Consequently an implementation may 412 * acquire the file lock in a background thread or from a task executed by 413 * a thread in the associated thread pool. If there are many lock operations 414 * outstanding then it may consume threads in the Java virtual machine for 415 * indefinite periods. 416 * 417 * <p> Some operating systems do not support shared locks, in which case a 418 * request for a shared lock is automatically converted into a request for 419 * an exclusive lock. Whether the newly-acquired lock is shared or 420 * exclusive may be tested by invoking the resulting lock object's {@link 421 * FileLock#isShared() isShared} method. 422 * 423 * <p> File locks are held on behalf of the entire Java virtual machine. 424 * They are not suitable for controlling access to a file by multiple 425 * threads within the same virtual machine. 426 * 427 * @param position 428 * The position at which the locked region is to start; must be 429 * non-negative 430 * @param size 431 * The size of the locked region; must be non-negative, and the sum 432 * {@code position} + {@code size} must be non-negative 433 * @param shared 434 * {@code true} to request a shared lock, in which case this 435 * channel must be open for reading (and possibly writing); 436 * {@code false} to request an exclusive lock, in which case this 437 * channel must be open for writing (and possibly reading) 438 * @param attachment 439 * The object to attach to the I/O operation; can be {@code null} 440 * @param handler 441 * The handler for consuming the result 442 * 443 * @throws OverlappingFileLockException 444 * If a lock that overlaps the requested region is already held by 445 * this Java virtual machine, or there is already a pending attempt 446 * to lock an overlapping region 447 * @throws IllegalArgumentException 448 * If the preconditions on the parameters do not hold 449 * @throws NonReadableChannelException 450 * If {@code shared} is true but this channel was not opened for reading 451 * @throws NonWritableChannelException 452 * If {@code shared} is false but this channel was not opened for writing 453 */ 454 public abstract <A> void lock(long position, 455 long size, 456 boolean shared, 457 A attachment, 458 CompletionHandler<FileLock,? super A> handler); 459 460 /** 461 * Acquires an exclusive lock on this channel's file. 462 * 463 * <p> This method initiates an operation to acquire a lock on the given 464 * region of this channel's file. The {@code handler} parameter is a 465 * completion handler that is invoked when the lock is acquired (or the 466 * operation fails). The result passed to the completion handler is the 467 * resulting {@code FileLock}. 468 * 469 * <p> An invocation of this method of the form {@code ch.lock(att,handler)} 470 * behaves in exactly the same way as the invocation 471 * <pre> 472 * ch.{@link #lock(long,long,boolean,Object,CompletionHandler) lock}(0L, Long.MAX_VALUE, false, att, handler) 473 * </pre> 474 * 475 * @param attachment 476 * The object to attach to the I/O operation; can be {@code null} 477 * @param handler 478 * The handler for consuming the result 479 * 480 * @throws OverlappingFileLockException 481 * If a lock is already held by this Java virtual machine, or there 482 * is already a pending attempt to lock a region 483 * @throws NonWritableChannelException 484 * If this channel was not opened for writing 485 */ 486 public final <A> void lock(A attachment, 487 CompletionHandler<FileLock,? super A> handler) 488 { 489 lock(0L, Long.MAX_VALUE, false, attachment, handler); 490 } 491 492 /** 493 * Acquires a lock on the given region of this channel's file. 494 * 495 * <p> This method initiates an operation to acquire a lock on the given 496 * region of this channel's file. The method behaves in exactly the same 497 * manner as the {@link #lock(long, long, boolean, Object, CompletionHandler)} 498 * method except that instead of specifying a completion handler, this 499 * method returns a {@code Future} representing the pending result. The 500 * {@code Future}'s {@link Future#get() get} method returns the {@link 501 * FileLock} on successful completion. 502 * 503 * @param position 504 * The position at which the locked region is to start; must be 505 * non-negative 506 * @param size 507 * The size of the locked region; must be non-negative, and the sum 508 * {@code position} + {@code size} must be non-negative 509 * @param shared 510 * {@code true} to request a shared lock, in which case this 511 * channel must be open for reading (and possibly writing); 512 * {@code false} to request an exclusive lock, in which case this 513 * channel must be open for writing (and possibly reading) 514 * 515 * @return a {@code Future} object representing the pending result 516 * 517 * @throws OverlappingFileLockException 518 * If a lock is already held by this Java virtual machine, or there 519 * is already a pending attempt to lock a region 520 * @throws IllegalArgumentException 521 * If the preconditions on the parameters do not hold 522 * @throws NonReadableChannelException 523 * If {@code shared} is true but this channel was not opened for reading 524 * @throws NonWritableChannelException 525 * If {@code shared} is false but this channel was not opened for writing 526 */ 527 public abstract Future<FileLock> lock(long position, long size, boolean shared); 528 529 /** 530 * Acquires an exclusive lock on this channel's file. 531 * 532 * <p> This method initiates an operation to acquire an exclusive lock on this 533 * channel's file. The method returns a {@code Future} representing the 534 * pending result of the operation. The {@code Future}'s {@link Future#get() 535 * get} method returns the {@link FileLock} on successful completion. 536 * 537 * <p> An invocation of this method behaves in exactly the same way as the 538 * invocation 539 * <pre> 540 * ch.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) 541 * </pre> 542 * 543 * @return a {@code Future} object representing the pending result 544 * 545 * @throws OverlappingFileLockException 546 * If a lock is already held by this Java virtual machine, or there 547 * is already a pending attempt to lock a region 548 * @throws NonWritableChannelException 549 * If this channel was not opened for writing 550 */ 551 public final Future<FileLock> lock() { 552 return lock(0L, Long.MAX_VALUE, false); 553 } 554 555 /** 556 * Attempts to acquire a lock on the given region of this channel's file. 557 * 558 * <p> This method does not block. An invocation always returns immediately, 559 * either having acquired a lock on the requested region or having failed to 560 * do so. If it fails to acquire a lock because an overlapping lock is held 561 * by another program then it returns {@code null}. If it fails to acquire 562 * a lock for any other reason then an appropriate exception is thrown. 563 * 564 * @param position 565 * The position at which the locked region is to start; must be 566 * non-negative 567 * 568 * @param size 569 * The size of the locked region; must be non-negative, and the sum 570 * {@code position} + {@code size} must be non-negative 571 * 572 * @param shared 573 * {@code true} to request a shared lock, 574 * {@code false} to request an exclusive lock 575 * 576 * @return A lock object representing the newly-acquired lock, 577 * or {@code null} if the lock could not be acquired 578 * because another program holds an overlapping lock 579 * 580 * @throws IllegalArgumentException 581 * If the preconditions on the parameters do not hold 582 * @throws ClosedChannelException 583 * If this channel is closed 584 * @throws OverlappingFileLockException 585 * If a lock that overlaps the requested region is already held by 586 * this Java virtual machine, or if another thread is already 587 * blocked in this method and is attempting to lock an overlapping 588 * region of the same file 589 * @throws NonReadableChannelException 590 * If {@code shared} is true but this channel was not opened for reading 591 * @throws NonWritableChannelException 592 * If {@code shared} is false but this channel was not opened for writing 593 * 594 * @throws IOException 595 * If some other I/O error occurs 596 * 597 * @see #lock(Object,CompletionHandler) 598 * @see #lock(long,long,boolean,Object,CompletionHandler) 599 * @see #tryLock() 600 */ 601 public abstract FileLock tryLock(long position, long size, boolean shared) 602 throws IOException; 603 604 /** 605 * Attempts to acquire an exclusive lock on this channel's file. 606 * 607 * <p> An invocation of this method of the form {@code ch.tryLock()} 608 * behaves in exactly the same way as the invocation 609 * 610 * <pre> 611 * ch.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre> 612 * 613 * @return A lock object representing the newly-acquired lock, 614 * or {@code null} if the lock could not be acquired 615 * because another program holds an overlapping lock 616 * 617 * @throws ClosedChannelException 618 * If this channel is closed 619 * @throws OverlappingFileLockException 620 * If a lock that overlaps the requested region is already held by 621 * this Java virtual machine, or if another thread is already 622 * blocked in this method and is attempting to lock an overlapping 623 * region 624 * @throws NonWritableChannelException 625 * If {@code shared} is false but this channel was not opened for writing 626 * 627 * @throws IOException 628 * If some other I/O error occurs 629 * 630 * @see #lock(Object,CompletionHandler) 631 * @see #lock(long,long,boolean,Object,CompletionHandler) 632 * @see #tryLock(long,long,boolean) 633 */ 634 public final FileLock tryLock() throws IOException { 635 return tryLock(0L, Long.MAX_VALUE, false); 636 } 637 638 /** 639 * Reads a sequence of bytes from this channel into the given buffer, 640 * starting at the given file position. 641 * 642 * <p> This method initiates the reading of a sequence of bytes from this 643 * channel into the given buffer, starting at the given file position. The 644 * result of the read is the number of bytes read or {@code -1} if the given 645 * position is greater than or equal to the file's size at the time that the 646 * read is attempted. 647 * 648 * <p> This method works in the same manner as the {@link 649 * AsynchronousByteChannel#read(ByteBuffer,Object,CompletionHandler)} 650 * method, except that bytes are read starting at the given file position. 651 * If the given file position is greater than the file's size at the time 652 * that the read is attempted then no bytes are read. 653 * 654 * @param dst 655 * The buffer into which bytes are to be transferred 656 * @param position 657 * The file position at which the transfer is to begin; 658 * must be non-negative 659 * @param attachment 660 * The object to attach to the I/O operation; can be {@code null} 661 * @param handler 662 * The handler for consuming the result 663 * 664 * @throws IllegalArgumentException 665 * If the position is negative or the buffer is read-only 666 * @throws NonReadableChannelException 667 * If this channel was not opened for reading 668 */ 669 public abstract <A> void read(ByteBuffer dst, 670 long position, 671 A attachment, 672 CompletionHandler<Integer,? super A> handler); 673 674 /** 675 * Reads a sequence of bytes from this channel into the given buffer, 676 * starting at the given file position. 677 * 678 * <p> This method initiates the reading of a sequence of bytes from this 679 * channel into the given buffer, starting at the given file position. This 680 * method returns a {@code Future} representing the pending result of the 681 * operation. The {@code Future}'s {@link Future#get() get} method returns 682 * the number of bytes read or {@code -1} if the given position is greater 683 * than or equal to the file's size at the time that the read is attempted. 684 * 685 * <p> This method works in the same manner as the {@link 686 * AsynchronousByteChannel#read(ByteBuffer)} method, except that bytes are 687 * read starting at the given file position. If the given file position is 688 * greater than the file's size at the time that the read is attempted then 689 * no bytes are read. 690 * 691 * @param dst 692 * The buffer into which bytes are to be transferred 693 * @param position 694 * The file position at which the transfer is to begin; 695 * must be non-negative 696 * 697 * @return A {@code Future} object representing the pending result 698 * 699 * @throws IllegalArgumentException 700 * If the position is negative or the buffer is read-only 701 * @throws NonReadableChannelException 702 * If this channel was not opened for reading 703 */ 704 public abstract Future<Integer> read(ByteBuffer dst, long position); 705 706 /** 707 * Writes a sequence of bytes to this channel from the given buffer, starting 708 * at the given file position. 709 * 710 * <p> This method works in the same manner as the {@link 711 * AsynchronousByteChannel#write(ByteBuffer,Object,CompletionHandler)} 712 * method, except that bytes are written starting at the given file position. 713 * If the given position is greater than the file's size, at the time that 714 * the write is attempted, then the file will be grown to accommodate the new 715 * bytes; the values of any bytes between the previous end-of-file and the 716 * newly-written bytes are unspecified. 717 * 718 * @param src 719 * The buffer from which bytes are to be transferred 720 * @param position 721 * The file position at which the transfer is to begin; 722 * must be non-negative 723 * @param attachment 724 * The object to attach to the I/O operation; can be {@code null} 725 * @param handler 726 * The handler for consuming the result 727 * 728 * @throws IllegalArgumentException 729 * If the position is negative 730 * @throws NonWritableChannelException 731 * If this channel was not opened for writing 732 */ 733 public abstract <A> void write(ByteBuffer src, 734 long position, 735 A attachment, 736 CompletionHandler<Integer,? super A> handler); 737 738 /** 739 * Writes a sequence of bytes to this channel from the given buffer, starting 740 * at the given file position. 741 * 742 * <p> This method initiates the writing of a sequence of bytes to this 743 * channel from the given buffer, starting at the given file position. The 744 * method returns a {@code Future} representing the pending result of the 745 * write operation. The {@code Future}'s {@link Future#get() get} method 746 * returns the number of bytes written. 747 * 748 * <p> This method works in the same manner as the {@link 749 * AsynchronousByteChannel#write(ByteBuffer)} method, except that bytes are 750 * written starting at the given file position. If the given position is 751 * greater than the file's size, at the time that the write is attempted, 752 * then the file will be grown to accommodate the new bytes; the values of 753 * any bytes between the previous end-of-file and the newly-written bytes 754 * are unspecified. 755 * 756 * @param src 757 * The buffer from which bytes are to be transferred 758 * @param position 759 * The file position at which the transfer is to begin; 760 * must be non-negative 761 * 762 * @return A {@code Future} object representing the pending result 763 * 764 * @throws IllegalArgumentException 765 * If the position is negative 766 * @throws NonWritableChannelException 767 * If this channel was not opened for writing 768 */ 769 public abstract Future<Integer> write(ByteBuffer src, long position); 770 }