1 /*
2 * Copyright (c) 2000, 2023, 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
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24 */
25
26 package java.nio.channels;
27
28 import java.io.IOException;
29 import java.lang.foreign.Arena;
30 import java.lang.foreign.MemorySegment;
31 import java.nio.ByteBuffer;
32 import java.nio.MappedByteBuffer;
33 import java.nio.channels.spi.AbstractInterruptibleChannel;
34 import java.nio.file.FileAlreadyExistsException;
35 import java.nio.file.OpenOption;
36 import java.nio.file.Path;
37 import java.nio.file.StandardOpenOption;
38 import java.nio.file.attribute.FileAttribute;
39 import java.nio.file.spi.FileSystemProvider;
40 import java.util.Set;
41 import java.util.HashSet;
42 import java.util.Collections;
43 import jdk.internal.javac.PreviewFeature;
44
45 /**
46 * A channel for reading, writing, mapping, and manipulating a file.
47 *
48 * <p> A file channel is a {@link SeekableByteChannel} that is connected to
49 * a file. It has a current <i>position</i> within its file which can
50 * be both {@link #position() <i>queried</i>} and {@link #position(long)
51 * <i>modified</i>}. The file itself contains a variable-length sequence
52 * of bytes that can be read and written and whose current {@link #size
53 * <i>size</i>} can be queried. The size of the file increases
54 * when bytes are written beyond its current size; the size of the file
55 * decreases when it is {@link #truncate <i>truncated</i>}. The
56 * file may also have some associated <i>metadata</i> such as access
57 * permissions, content type, and last-modification time; this class does not
58 * define methods for metadata access.
59 *
60 * <p> In addition to the familiar read, write, and close operations of byte
61 * channels, this class defines the following file-specific operations: </p>
62 *
63 * <ul>
64 *
65 * <li><p> Bytes may be {@link #read(ByteBuffer, long) read} or
66 * {@link #write(ByteBuffer, long) <i>written</i>} at an absolute
67 * position in a file in a way that does not affect the channel's current
68 * position. </p></li>
69 *
70 * <li><p> A region of a file may be {@link #map <i>mapped</i>}
71 * directly into memory; for large files this is often much more efficient
72 * than invoking the usual {@code read} or {@code write} methods.
73 * </p></li>
74 *
75 * <li><p> Updates made to a file may be {@link #force <i>forced
76 * out</i>} to the underlying storage device, ensuring that data are not
77 * lost in the event of a system crash. </p></li>
78 *
79 * <li><p> Bytes can be transferred from a file {@link #transferTo <i>to
80 * some other channel</i>}, and {@link #transferFrom <i>vice
81 * versa</i>}, in a way that can be optimized by many operating systems
82 * into a very fast transfer directly to or from the filesystem cache.
83 * </p></li>
84 *
85 * <li><p> A region of a file may be {@link FileLock <i>locked</i>}
86 * against access by other programs. </p></li>
87 *
88 * </ul>
89 *
90 * <p> File channels are safe for use by multiple concurrent threads. The
91 * {@link Channel#close close} method may be invoked at any time, as specified
92 * by the {@link Channel} interface. Only one operation that involves the
93 * channel's position or can change its file's size may be in progress at any
94 * given time; attempts to initiate a second such operation while the first is
95 * still in progress will block until the first operation completes. Other
96 * operations, in particular those that take an explicit position, may proceed
97 * concurrently; whether they in fact do so is dependent upon the underlying
98 * implementation and is therefore unspecified.
99 *
100 * <p> The view of a file provided by an instance of this class is guaranteed
101 * to be consistent with other views of the same file provided by other
102 * instances in the same program. The view provided by an instance of this
103 * class may or may not, however, be consistent with the views seen by other
104 * concurrently-running programs due to caching performed by the underlying
105 * operating system and delays induced by network-filesystem protocols. This
106 * 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 * <p> A file channel is created by invoking one of the {@link #open open}
112 * methods defined by this class. A file channel can also be obtained from an
113 * existing {@link java.io.FileInputStream#getChannel FileInputStream}, {@link
114 * java.io.FileOutputStream#getChannel FileOutputStream}, or {@link
115 * java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking
116 * that object's {@code getChannel} method, which returns a file channel that
117 * is connected to the same underlying file. Where the file channel is obtained
118 * from an existing stream or random access file then the state of the file
119 * channel is intimately connected to that of the object whose {@code getChannel}
120 * method returned the channel. Changing the channel's position, whether
121 * explicitly or by reading or writing bytes, will change the file position of
122 * the originating object, and vice versa. Changing the file's length via the
123 * file channel will change the length seen via the originating object, and vice
124 * versa. Changing the file's content by writing bytes will change the content
125 * seen by the originating object, and vice versa. Closing the channel will
126 * close the originating object.
127 *
128 * <a id="open-mode"></a> <p> At various points this class specifies that an
129 * instance that is "open for reading," "open for writing," or "open for
130 * reading and writing" is required. A channel obtained via the {@link
131 * java.io.FileInputStream#getChannel getChannel} method of a {@link
132 * java.io.FileInputStream} instance will be open for reading. A channel
133 * obtained via the {@link java.io.FileOutputStream#getChannel getChannel}
134 * method of a {@link java.io.FileOutputStream} instance will be open for
135 * writing. Finally, a channel obtained via the {@link
136 * java.io.RandomAccessFile#getChannel getChannel} method of a {@link
137 * java.io.RandomAccessFile} instance will be open for reading if the instance
138 * was created with mode {@code "r"} and will be open for reading and writing
139 * if the instance was created with mode {@code "rw"}.
140 *
141 * <a id="append-mode"></a><p> A file channel that is open for writing may be in
142 * <i>append mode</i>, for example if it was obtained from a file-output stream
143 * that was created by invoking the {@link
144 * java.io.FileOutputStream#FileOutputStream(java.io.File,boolean)
145 * FileOutputStream(File,boolean)} constructor and passing {@code true} for
146 * the second parameter. In this mode each invocation of a relative write
147 * operation first advances the position to the end of the file and then writes
148 * the requested data. Whether the advancement of the position and the writing
149 * of the data are done in a single atomic operation is system-dependent and
150 * therefore unspecified. In this mode the behavior of the method to
151 * {@linkplain #write(ByteBuffer,long) write at a given position} is also
152 * system-dependent.
153 *
154 * @see java.io.FileInputStream#getChannel()
155 * @see java.io.FileOutputStream#getChannel()
156 * @see java.io.RandomAccessFile#getChannel()
157 *
158 * @author Mark Reinhold
159 * @author Mike McCloskey
160 * @author JSR-51 Expert Group
161 * @since 1.4
162 */
163
164 public abstract class FileChannel
165 extends AbstractInterruptibleChannel
166 implements SeekableByteChannel, GatheringByteChannel, ScatteringByteChannel
167 {
168 /**
169 * Initializes a new instance of this class.
170 */
171 protected FileChannel() { }
172
173 /**
174 * Opens or creates a file, returning a file channel to access the file.
175 *
176 * <p> The {@code options} parameter determines how the file is opened.
177 * The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE
178 * WRITE} options determine if the file should be opened for reading and/or
179 * writing. If neither option (or the {@link StandardOpenOption#APPEND APPEND}
180 * option) is contained in the array then the file is opened for reading.
181 * By default reading or writing commences at the beginning of the file.
182 *
183 * <p> In the addition to {@code READ} and {@code WRITE}, the following
184 * options may be present:
185 *
186 * <table class="striped">
187 * <caption style="display:none">additional options</caption>
188 * <thead>
189 * <tr> <th scope="col">Option</th> <th scope="col">Description</th> </tr>
190 * </thead>
191 * <tbody>
192 * <tr>
193 * <th scope="row"> {@link StandardOpenOption#APPEND APPEND} </th>
194 * <td> If this option is present then the file is opened for writing and
195 * each invocation of the channel's {@code write} method first advances
196 * the position to the end of the file and then writes the requested
197 * data. Whether the advancement of the position and the writing of the
198 * data are done in a single atomic operation is system-dependent and
199 * therefore unspecified. The effect of {@linkplain
200 * #write(ByteBuffer,long) writing at a given position} with this option
201 * present is unspecified. This option may not be used in conjunction
202 * with the {@code READ} or {@code TRUNCATE_EXISTING} options. </td>
203 * </tr>
204 * <tr>
205 * <th scope="row"> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </th>
206 * <td> If this option is present then the existing file is truncated to
207 * a size of 0 bytes. This option is ignored when the file is opened only
208 * for reading. </td>
209 * </tr>
210 * <tr>
211 * <th scope="row"> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </th>
212 * <td> If this option is present then a new file is created, failing if
213 * the file already exists. When creating a file the check for the
214 * existence of the file and the creation of the file if it does not exist
215 * is atomic with respect to other file system operations. This option is
216 * ignored when the file is opened only for reading. </td>
217 * </tr>
218 * <tr>
219 * <th scope="row" > {@link StandardOpenOption#CREATE CREATE} </th>
220 * <td> If this option is present then an existing file is opened if it
221 * exists, otherwise a new file is created. When creating a file the check
222 * for the existence of the file and the creation of the file if it does
223 * not exist is atomic with respect to other file system operations. This
224 * option is ignored if the {@code CREATE_NEW} option is also present or
225 * the file is opened only for reading. </td>
226 * </tr>
227 * <tr>
228 * <th scope="row" > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </th>
229 * <td> When this option is present then the implementation makes a
230 * <em>best effort</em> attempt to delete the file when closed by
231 * the {@link #close close} method. If the {@code close} method is not
232 * invoked then a <em>best effort</em> attempt is made to delete the file
233 * when the Java virtual machine terminates. </td>
234 * </tr>
235 * <tr>
236 * <th scope="row">{@link StandardOpenOption#SPARSE SPARSE} </th>
237 * <td> When creating a new file this option is a <em>hint</em> that the
238 * new file will be sparse. This option is ignored when not creating
239 * a new file. </td>
240 * </tr>
241 * <tr>
242 * <th scope="row"> {@link StandardOpenOption#SYNC SYNC} </th>
243 * <td> Requires that every update to the file's content or metadata be
244 * written synchronously to the underlying storage device. (see <a
245 * href="../file/package-summary.html#integrity"> Synchronized I/O file
246 * integrity</a>). </td>
247 * </tr>
248 * <tr>
249 * <th scope="row"> {@link StandardOpenOption#DSYNC DSYNC} </th>
250 * <td> Requires that every update to the file's content be written
251 * synchronously to the underlying storage device. (see <a
252 * href="../file/package-summary.html#integrity"> Synchronized I/O file
253 * integrity</a>). </td>
254 * </tr>
255 * </tbody>
256 * </table>
257 *
258 * <p> An implementation may also support additional options.
259 *
260 * <p> The {@code attrs} parameter is an optional array of file {@link
261 * FileAttribute file-attributes} to set atomically when creating the file.
262 *
263 * <p> The new channel is created by invoking the {@link
264 * FileSystemProvider#newFileChannel newFileChannel} method on the
265 * provider that created the {@code Path}.
266 *
267 * @param path
268 * The path of the file to open or create
269 * @param options
270 * Options specifying how the file is opened
271 * @param attrs
272 * An optional list of file attributes to set atomically when
273 * creating the file
274 *
275 * @return A new file channel
276 *
277 * @throws IllegalArgumentException
278 * If the set contains an invalid combination of options
279 * @throws UnsupportedOperationException
280 * If the {@code path} is associated with a provider that does not
281 * support creating file channels, or an unsupported open option is
282 * specified, or the array contains an attribute that cannot be set
283 * atomically when creating the file
284 * @throws FileAlreadyExistsException
285 * If a file of that name already exists and the {@link
286 * StandardOpenOption#CREATE_NEW CREATE_NEW} option is specified
287 * and the file is being opened for writing
288 * <i>(<a href="../file/package-summary.html#optspecex">optional
289 * specific exception</a>)</i>
290 * @throws IOException
291 * If an I/O error occurs
292 * @throws SecurityException
293 * If a security manager is installed and it denies an
294 * unspecified permission required by the implementation.
295 * In the case of the default provider, the {@link
296 * SecurityManager#checkRead(String)} method is invoked to check
297 * read access if the file is opened for reading. The {@link
298 * SecurityManager#checkWrite(String)} method is invoked to check
299 * write access if the file is opened for writing
300 *
301 * @since 1.7
302 */
303 public static FileChannel open(Path path,
304 Set<? extends OpenOption> options,
305 FileAttribute<?>... attrs)
306 throws IOException
307 {
308 FileSystemProvider provider = path.getFileSystem().provider();
309 return provider.newFileChannel(path, options, attrs);
310 }
311
312 @SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
313 private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];
314
315 /**
316 * Opens or creates a file, returning a file channel to access the file.
317 *
318 * <p> An invocation of this method behaves in exactly the same way as the
319 * invocation
320 * {@snippet lang=java :
321 * // @link substring="open" target="#open(Path,Set,FileAttribute[])" :
322 * fc.open(file, opts, new FileAttribute<?>[0]);
323 * }
324 * where {@code opts} is a set of the options specified in the {@code
325 * options} array.
326 *
327 * @param path
328 * The path of the file to open or create
329 * @param options
330 * Options specifying how the file is opened
331 *
332 * @return A new file channel
333 *
334 * @throws IllegalArgumentException
335 * If the set contains an invalid combination of options
336 * @throws UnsupportedOperationException
337 * If the {@code path} is associated with a provider that does not
338 * support creating file channels, or an unsupported open option is
339 * specified
340 * @throws FileAlreadyExistsException
341 * If a file of that name already exists and the {@link
342 * StandardOpenOption#CREATE_NEW CREATE_NEW} option is specified
343 * and the file is being opened for writing
344 * <i>(<a href="../file/package-summary.html#optspecex">optional
345 * specific exception</a>)</i>
346 * @throws IOException
347 * If an I/O error occurs
348 * @throws SecurityException
349 * If a security manager is installed and it denies an
350 * unspecified permission required by the implementation.
351 * In the case of the default provider, the {@link
352 * SecurityManager#checkRead(String)} method is invoked to check
353 * read access if the file is opened for reading. The {@link
354 * SecurityManager#checkWrite(String)} method is invoked to check
355 * write access if the file is opened for writing
356 *
357 * @since 1.7
358 */
359 public static FileChannel open(Path path, OpenOption... options)
360 throws IOException
361 {
362 Set<OpenOption> set;
363 if (options.length == 0) {
364 set = Collections.emptySet();
365 } else {
366 set = new HashSet<>();
367 Collections.addAll(set, options);
368 }
369 return open(path, set, NO_ATTRIBUTES);
370 }
371
372 // -- Channel operations --
373
374 /**
375 * Reads a sequence of bytes from this channel into the given buffer.
376 *
377 * <p> Bytes are read starting at this channel's current file position, and
378 * then the file position is updated with the number of bytes actually
379 * read. Otherwise this method behaves exactly as specified in the {@link
380 * ReadableByteChannel} interface. </p>
381 *
382 * @throws ClosedChannelException {@inheritDoc}
383 * @throws AsynchronousCloseException {@inheritDoc}
384 * @throws ClosedByInterruptException {@inheritDoc}
385 * @throws NonReadableChannelException {@inheritDoc}
386 */
387 public abstract int read(ByteBuffer dst) throws IOException;
388
389 /**
390 * Reads a sequence of bytes from this channel into a subsequence of the
391 * given buffers.
392 *
393 * <p> Bytes are read starting at this channel's current file position, and
394 * then the file position is updated with the number of bytes actually
395 * read. Otherwise this method behaves exactly as specified in the {@link
396 * ScatteringByteChannel} interface. </p>
397 *
398 * @throws ClosedChannelException {@inheritDoc}
399 * @throws AsynchronousCloseException {@inheritDoc}
400 * @throws ClosedByInterruptException {@inheritDoc}
401 * @throws NonReadableChannelException {@inheritDoc}
402 */
403 public abstract long read(ByteBuffer[] dsts, int offset, int length)
404 throws IOException;
405
406 /**
407 * Reads a sequence of bytes from this channel into the given buffers.
408 *
409 * <p> Bytes are read starting at this channel's current file position, and
410 * then the file position is updated with the number of bytes actually
411 * read. Otherwise this method behaves exactly as specified in the {@link
412 * ScatteringByteChannel} interface. </p>
413 *
414 * @throws ClosedChannelException {@inheritDoc}
415 * @throws AsynchronousCloseException {@inheritDoc}
416 * @throws ClosedByInterruptException {@inheritDoc}
417 * @throws NonReadableChannelException {@inheritDoc}
418 */
419 public final long read(ByteBuffer[] dsts) throws IOException {
420 return read(dsts, 0, dsts.length);
421 }
422
423 /**
424 * Writes a sequence of bytes to this channel from the given buffer.
425 *
426 * <p> Bytes are written starting at this channel's current file position
427 * unless the channel is in append mode, in which case the position is
428 * first advanced to the end of the file. The file is grown, if necessary,
429 * to accommodate the written bytes, and then the file position is updated
430 * with the number of bytes actually written. Otherwise this method
431 * behaves exactly as specified by the {@link WritableByteChannel}
432 * interface. </p>
433 *
434 * @throws ClosedChannelException {@inheritDoc}
435 * @throws AsynchronousCloseException {@inheritDoc}
436 * @throws ClosedByInterruptException {@inheritDoc}
437 * @throws NonWritableChannelException {@inheritDoc}
438 */
439 public abstract int write(ByteBuffer src) throws IOException;
440
441 /**
442 * Writes a sequence of bytes to this channel from a subsequence of the
443 * given buffers.
444 *
445 * <p> Bytes are written starting at this channel's current file position
446 * unless the channel is in append mode, in which case the position is
447 * first advanced to the end of the file. The file is grown, if necessary,
448 * to accommodate the written bytes, and then the file position is updated
449 * with the number of bytes actually written. Otherwise this method
450 * behaves exactly as specified in the {@link GatheringByteChannel}
451 * interface. </p>
452 *
453 * @throws ClosedChannelException {@inheritDoc}
454 * @throws AsynchronousCloseException {@inheritDoc}
455 * @throws ClosedByInterruptException {@inheritDoc}
456 * @throws NonWritableChannelException {@inheritDoc}
457 */
458 public abstract long write(ByteBuffer[] srcs, int offset, int length)
459 throws IOException;
460
461 /**
462 * Writes a sequence of bytes to this channel from the given buffers.
463 *
464 * <p> Bytes are written starting at this channel's current file position
465 * unless the channel is in append mode, in which case the position is
466 * first advanced to the end of the file. The file is grown, if necessary,
467 * to accommodate the written bytes, and then the file position is updated
468 * with the number of bytes actually written. Otherwise this method
469 * behaves exactly as specified in the {@link GatheringByteChannel}
470 * interface. </p>
471 *
472 * @throws ClosedChannelException {@inheritDoc}
473 * @throws AsynchronousCloseException {@inheritDoc}
474 * @throws ClosedByInterruptException {@inheritDoc}
475 * @throws NonWritableChannelException {@inheritDoc}
476 */
477 public final long write(ByteBuffer[] srcs) throws IOException {
478 return write(srcs, 0, srcs.length);
479 }
480
481
482 // -- Other operations --
483
484 /**
485 * Returns this channel's file position.
486 *
487 * @return This channel's file position,
488 * a non-negative integer counting the number of bytes
489 * from the beginning of the file to the current position
490 *
491 * @throws ClosedChannelException
492 * If this channel is closed
493 *
494 * @throws IOException
495 * If some other I/O error occurs
496 */
497 public abstract long position() throws IOException;
498
499 /**
500 * Sets this channel's file position.
501 *
502 * <p> Setting the position to a value that is greater than the file's
503 * current size is legal but does not change the size of the file. A later
504 * attempt to read bytes at such a position will immediately return an
505 * end-of-file indication. A later attempt to write bytes at such a
506 * position will cause the file to be grown to accommodate the new bytes;
507 * the values of any bytes between the previous end-of-file and the
508 * newly-written bytes are unspecified. </p>
509 *
510 * @param newPosition
511 * The new position, a non-negative integer counting
512 * the number of bytes from the beginning of the file
513 *
514 * @return This file channel
515 *
516 * @throws ClosedChannelException
517 * If this channel is closed
518 *
519 * @throws IllegalArgumentException
520 * If the new position is negative
521 *
522 * @throws IOException
523 * If some other I/O error occurs
524 */
525 public abstract FileChannel position(long newPosition) throws IOException;
526
527 /**
528 * Returns the current size of this channel's file.
529 *
530 * @return The current size of this channel's file,
531 * measured in bytes
532 *
533 * @throws ClosedChannelException
534 * If this channel is closed
535 *
536 * @throws IOException
537 * If some other I/O error occurs
538 */
539 public abstract long size() throws IOException;
540
541 /**
542 * Truncates this channel's file to the given size.
543 *
544 * <p> If the given size is less than the file's current size then the file
545 * is truncated, discarding any bytes beyond the new end of the file. If
546 * the given size is greater than or equal to the file's current size then
547 * the file is not modified. In either case, if this channel's file
548 * position is greater than the given size then it is set to that size.
549 * </p>
550 *
551 * @param size
552 * The new size, a non-negative byte count
553 *
554 * @return This file channel
555 *
556 * @throws NonWritableChannelException
557 * If this channel was not opened for writing
558 *
559 * @throws ClosedChannelException
560 * If this channel is closed
561 *
562 * @throws IllegalArgumentException
563 * If the new size is negative
564 *
565 * @throws IOException
566 * If some other I/O error occurs
567 */
568 public abstract FileChannel truncate(long size) throws IOException;
569
570 /**
571 * Forces any updates to this channel's file to be written to the storage
572 * device that contains it.
573 *
574 * <p> If this channel's file resides on a local storage device then when
575 * this method returns it is guaranteed that all changes made to the file
576 * since this channel was created, or since this method was last invoked,
577 * will have been written to that device. This is useful for ensuring that
578 * critical information is not lost in the event of a system crash.
579 *
580 * <p> If the file does not reside on a local device then no such guarantee
581 * is made.
582 *
583 * <p> The {@code metaData} parameter can be used to limit the number of
584 * I/O operations that this method is required to perform. Passing
585 * {@code false} for this parameter indicates that only updates to the
586 * file's content need be written to storage; passing {@code true}
587 * indicates that updates to both the file's content and metadata must be
588 * written, which generally requires at least one more I/O operation.
589 * Whether this parameter actually has any effect is dependent upon the
590 * underlying operating system and is therefore unspecified.
591 *
592 * <p> Invoking this method may cause an I/O operation to occur even if the
593 * channel was only opened for reading. Some operating systems, for
594 * example, maintain a last-access time as part of a file's metadata, and
595 * this time is updated whenever the file is read. Whether or not this is
596 * actually done is system-dependent and is therefore unspecified.
597 *
598 * <p> This method is only guaranteed to force changes that were made to
599 * this channel's file via the methods defined in this class, or the methods
600 * defined by {@link java.io.FileOutputStream} or
601 * {@link java.io.RandomAccessFile} when the channel was obtained with the
602 * {@code getChannel} method. It may or may not force changes that were made
603 * by modifying the content of a
604 * {@link MappedByteBuffer <i>mapped byte buffer</i>} obtained by
605 * invoking the {@link #map map} method. Invoking the {@link
606 * MappedByteBuffer#force force} method of the mapped byte buffer will
607 * force changes made to the buffer's content to be written. </p>
608 *
609 * @param metaData
610 * If {@code true} then this method is required to force changes
611 * to both the file's content and metadata to be written to
612 * storage; otherwise, it need only force content changes to be
613 * written
614 *
615 * @throws ClosedChannelException
616 * If this channel is closed
617 *
618 * @throws IOException
619 * If some other I/O error occurs
620 */
621 public abstract void force(boolean metaData) throws IOException;
622
623 /**
624 * Transfers bytes from this channel's file to the given writable byte
625 * channel.
626 *
627 * <p> An attempt is made to read up to {@code count} bytes starting at
628 * the given {@code position} in this channel's file and write them to the
629 * target channel. An invocation of this method may or may not transfer
630 * all of the requested bytes; whether or not it does so depends upon the
631 * natures and states of the channels. Fewer than the requested number of
632 * bytes are transferred if this channel's file contains fewer than
633 * {@code count} bytes starting at the given {@code position}, or if the
634 * target channel is non-blocking and it has fewer than {@code count}
635 * bytes free in its output buffer.
636 *
637 * <p> This method does not modify this channel's position. If the given
638 * position is greater than or equal to the file's current size then no
639 * bytes are transferred. If the target channel has a position then bytes
640 * are written starting at that position and then the position
641 * is incremented by the number of bytes written.
642 *
643 * <p> This method is potentially much more efficient than a simple loop
644 * that reads from this channel and writes to the target channel. Many
645 * operating systems can transfer bytes directly from the filesystem cache
646 * to the target channel without actually copying them. </p>
647 *
648 * @param position
649 * The position within the file at which the transfer is to begin;
650 * must be non-negative
651 *
652 * @param count
653 * The maximum number of bytes to be transferred; must be
654 * non-negative
655 *
656 * @param target
657 * The target channel
658 *
659 * @return The number of bytes, possibly zero,
660 * that were actually transferred
661 *
662 * @throws IllegalArgumentException
663 * If the preconditions on the parameters do not hold
664 *
665 * @throws NonReadableChannelException
666 * If this channel was not opened for reading
667 *
668 * @throws NonWritableChannelException
669 * If the target channel was not opened for writing
670 *
671 * @throws ClosedChannelException
672 * If either this channel or the target channel is closed
673 *
674 * @throws AsynchronousCloseException
675 * If another thread closes either channel
676 * while the transfer is in progress
677 *
678 * @throws ClosedByInterruptException
679 * If another thread interrupts the current thread while the
680 * transfer is in progress, thereby closing both channels and
681 * setting the current thread's interrupt status
682 *
683 * @throws IOException
684 * If some other I/O error occurs
685 */
686 public abstract long transferTo(long position, long count,
687 WritableByteChannel target)
688 throws IOException;
689
690 /**
691 * Transfers bytes into this channel's file from the given readable byte
692 * channel.
693 *
694 * <p> An attempt is made to read up to {@code count} bytes from the
695 * source channel and write them to this channel's file starting at the
696 * given {@code position}. An invocation of this method may or may not
697 * transfer all of the requested bytes; whether or not it does so depends
698 * upon the natures and states of the channels. Fewer than the requested
699 * number of bytes will be transferred if the source channel has fewer than
700 * {@code count} bytes remaining, or if the source channel is non-blocking
701 * and has fewer than {@code count} bytes immediately available in its
702 * input buffer. No bytes are transferred, and zero is returned, if the
703 * source has reached end-of-stream.
704 *
705 * <p> This method does not modify this channel's position. If the given
706 * position is greater than or equal to the file's current size then the
707 * file will be grown to accommodate the new bytes; the values of any bytes
708 * between the previous end-of-file and the newly-written bytes are
709 * unspecified. If the source channel has a position then bytes are read
710 * starting at that position and then the position is incremented by the
711 * number of bytes read.
712 *
713 * <p> This method is potentially much more efficient than a simple loop
714 * that reads from the source channel and writes to this channel. Many
715 * operating systems can transfer bytes directly from the source channel
716 * into the filesystem cache without actually copying them. </p>
717 *
718 * @param src
719 * The source channel
720 *
721 * @param position
722 * The file position at which the transfer is to begin;
723 * must be non-negative
724 *
725 * @param count
726 * The maximum number of bytes to be transferred; must be
727 * non-negative
728 *
729 * @return The number of bytes, possibly zero,
730 * that were actually transferred
731 *
732 * @throws IllegalArgumentException
733 * If the preconditions on the parameters do not hold
734 *
735 * @throws NonReadableChannelException
736 * If the source channel was not opened for reading
737 *
738 * @throws NonWritableChannelException
739 * If this channel was not opened for writing
740 *
741 * @throws ClosedChannelException
742 * If either this channel or the source channel is closed
743 *
744 * @throws AsynchronousCloseException
745 * If another thread closes either channel
746 * while the transfer is in progress
747 *
748 * @throws ClosedByInterruptException
749 * If another thread interrupts the current thread while the
750 * transfer is in progress, thereby closing both channels and
751 * setting the current thread's interrupt status
752 *
753 * @throws IOException
754 * If some other I/O error occurs
755 */
756 public abstract long transferFrom(ReadableByteChannel src,
757 long position, long count)
758 throws IOException;
759
760 /**
761 * Reads a sequence of bytes from this channel into the given buffer,
762 * starting at the given file position.
763 *
764 * <p> This method works in the same manner as the {@link
765 * #read(ByteBuffer)} method, except that bytes are read starting at the
766 * given file position rather than at the channel's current position. This
767 * method does not modify this channel's position. If the given position
768 * is greater than or equal to the file's current size then no bytes are
769 * read. </p>
770 *
771 * @param dst
772 * The buffer into which bytes are to be transferred
773 *
774 * @param position
775 * The file position at which the transfer is to begin;
776 * must be non-negative
777 *
778 * @return The number of bytes read, possibly zero, or {@code -1} if the
779 * given position is greater than or equal to the file's current
780 * size
781 *
782 * @throws IllegalArgumentException
783 * If the position is negative or the buffer is read-only
784 *
785 * @throws NonReadableChannelException
786 * If this channel was not opened for reading
787 *
788 * @throws ClosedChannelException
789 * If this channel is closed
790 *
791 * @throws AsynchronousCloseException
792 * If another thread closes this channel
793 * while the read operation is in progress
794 *
795 * @throws ClosedByInterruptException
796 * If another thread interrupts the current thread
797 * while the read operation is in progress, thereby
798 * closing the channel and setting the current thread's
799 * interrupt status
800 *
801 * @throws IOException
802 * If some other I/O error occurs
803 */
804 public abstract int read(ByteBuffer dst, long position) throws IOException;
805
806 /**
807 * Writes a sequence of bytes to this channel from the given buffer,
808 * starting at the given file position.
809 *
810 * <p> This method works in the same manner as the {@link
811 * #write(ByteBuffer)} method, except that bytes are written starting at
812 * the given file position rather than at the channel's current position.
813 * This method does not modify this channel's position. If the given
814 * position is greater than or equal to the file's current size then the
815 * file will be grown to accommodate the new bytes; the values of any bytes
816 * between the previous end-of-file and the newly-written bytes are
817 * unspecified. </p>
818 *
819 * <p> If the file is open in <a href="#append-mode">append mode</a>, then
820 * the effect of invoking this method is unspecified.
821 *
822 * @param src
823 * The buffer from which bytes are to be transferred
824 *
825 * @param position
826 * The file position at which the transfer is to begin;
827 * must be non-negative
828 *
829 * @return The number of bytes written, possibly zero
830 *
831 * @throws IllegalArgumentException
832 * If the position is negative
833 *
834 * @throws NonWritableChannelException
835 * If this channel was not opened for writing
836 *
837 * @throws ClosedChannelException
838 * If this channel is closed
839 *
840 * @throws AsynchronousCloseException
841 * If another thread closes this channel
842 * while the write operation is in progress
843 *
844 * @throws ClosedByInterruptException
845 * If another thread interrupts the current thread
846 * while the write operation is in progress, thereby
847 * closing the channel and setting the current thread's
848 * interrupt status
849 *
850 * @throws IOException
851 * If some other I/O error occurs
852 */
853 public abstract int write(ByteBuffer src, long position) throws IOException;
854
855
856 // -- Memory-mapped buffers --
857
858 /**
859 * A file-mapping mode.
860 *
861 * @since 1.4
862 *
863 * @see java.nio.channels.FileChannel#map
864 */
865 public static class MapMode {
866
867 /**
868 * Mode for a read-only mapping.
869 */
870 public static final MapMode READ_ONLY
871 = new MapMode("READ_ONLY");
872
873 /**
874 * Mode for a read/write mapping.
875 */
876 public static final MapMode READ_WRITE
877 = new MapMode("READ_WRITE");
878
879 /**
880 * Mode for a private (copy-on-write) mapping.
881 */
882 public static final MapMode PRIVATE
883 = new MapMode("PRIVATE");
884
885 private final String name;
886
887 /**
888 * Constructs an instance of this class. This constructor may be used
889 * by code in java.base to create file mapping modes beyond the file
890 * mapping modes defined here.
891 * @param name the name of the map mode
892 */
893 private MapMode(String name) {
894 this.name = name;
895 }
896
897 /**
898 * Returns a string describing this file-mapping mode.
899 *
900 * @return A descriptive string
901 */
902 public String toString() {
903 return name;
904 }
905
906 }
907
908 /**
909 * Maps a region of this channel's file directly into memory.
910 *
911 * <p> The {@code mode} parameter specifies how the region of the file is
912 * mapped and may be one of the following modes:
913 *
914 * <ul>
915 *
916 * <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer
917 * will cause a {@link java.nio.ReadOnlyBufferException} to be thrown.
918 * ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li>
919 *
920 * <li><p> <i>Read/write:</i> Changes made to the resulting buffer will
921 * eventually be propagated to the file; they may or may not be made
922 * visible to other programs that have mapped the same file. ({@link
923 * MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li>
924 *
925 * <li><p> <i>Private:</i> Changes made to the resulting buffer will not
926 * be propagated to the file and will not be visible to other programs
927 * that have mapped the same file; instead, they will cause private
928 * copies of the modified portions of the buffer to be created. ({@link
929 * MapMode#PRIVATE MapMode.PRIVATE}) </p></li>
930 *
931 * </ul>
932 *
933 * <p> An implementation may support additional map modes.
934 *
935 * <p> For a read-only mapping, this channel must have been opened for
936 * reading; for a read/write or private mapping, this channel must have
937 * been opened for both reading and writing.
938 *
939 * <p> The {@link MappedByteBuffer <i>mapped byte buffer</i>}
940 * returned by this method will have a position of zero and a limit and
941 * capacity of {@code size}; its mark will be undefined. The buffer and
942 * the mapping that it represents will remain valid until the buffer itself
943 * is garbage-collected.
944 *
945 * <p> A mapping, once established, is not dependent upon the file channel
946 * that was used to create it. Closing the channel, in particular, has no
947 * effect upon the validity of the mapping.
948 *
949 * <p> Many of the details of memory-mapped files are inherently dependent
950 * upon the underlying operating system and are therefore unspecified. The
951 * behavior of this method when the requested region is not completely
952 * contained within this channel's file is unspecified. Whether changes
953 * made to the content or size of the underlying file, by this program or
954 * another, are propagated to the buffer is unspecified. The rate at which
955 * changes to the buffer are propagated to the file is unspecified.
956 *
957 * <p> For most operating systems, mapping a file into memory is more
958 * expensive than reading or writing a few tens of kilobytes of data via
959 * the usual {@link #read read} and {@link #write write} methods. From the
960 * standpoint of performance it is generally only worth mapping relatively
961 * large files into memory. </p>
962 *
963 * @param mode
964 * One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link
965 * MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE
966 * PRIVATE} defined in the {@link MapMode} class, according to
967 * whether the file is to be mapped read-only, read/write, or
968 * privately (copy-on-write), respectively, or an implementation
969 * specific map mode
970 *
971 * @param position
972 * The position within the file at which the mapped region
973 * is to start; must be non-negative
974 *
975 * @param size
976 * The size of the region to be mapped; must be non-negative and
977 * no greater than {@link java.lang.Integer#MAX_VALUE}
978 *
979 * @return The mapped byte buffer
980 *
981 * @throws NonReadableChannelException
982 * If the {@code mode} is {@link MapMode#READ_ONLY READ_ONLY} or
983 * an implementation specific map mode requiring read access,
984 * but this channel was not opened for reading
985 *
986 * @throws NonWritableChannelException
987 * If the {@code mode} is {@link MapMode#READ_WRITE READ_WRITE},
988 * {@link MapMode#PRIVATE PRIVATE} or an implementation specific
989 * map mode requiring write access, but this channel was not
990 * opened for both reading and writing
991 *
992 * @throws IllegalArgumentException
993 * If the preconditions on the parameters do not hold
994 *
995 * @throws UnsupportedOperationException
996 * If an unsupported map mode is specified
997 *
998 * @throws IOException
999 * If some other I/O error occurs
1000 *
1001 * @see java.nio.channels.FileChannel.MapMode
1002 * @see java.nio.MappedByteBuffer
1003 */
1004 public abstract MappedByteBuffer map(MapMode mode, long position, long size)
1005 throws IOException;
1006
1007 /**
1008 * Maps a region of this channel's file into a new mapped memory segment,
1009 * with the given offset, size and arena.
1010 * The {@linkplain MemorySegment#address() address} of the returned memory
1011 * segment is the starting address of the mapped off-heap region backing
1012 * the segment.
1013 * <p>
1014 * The lifetime of the returned segment is controlled by the provided arena.
1015 * For instance, if the provided arena is a closeable arena,
1016 * the returned segment will be unmapped when the provided closeable arena
1017 * is {@linkplain Arena#close() closed}.
1018 * <p> If the specified mapping mode is
1019 * {@linkplain FileChannel.MapMode#READ_ONLY READ_ONLY}, the resulting
1020 * segment will be read-only (see {@link MemorySegment#isReadOnly()}).
1021 *
1022 * <p> The content of a mapped memory segment can change at any time, for
1023 * example if the content of the corresponding region of the mapped file is
1024 * changed by this (or another) program. Whether such changes occur, and
1025 * when they occur, is operating-system dependent and therefore unspecified.
1026 *
1027 * <p> All or part of a mapped memory segment may become inaccessible at any
1028 * time, for example if the backing mapped file is truncated. An attempt to
1029 * access an inaccessible region of a mapped memory segment will not change
1030 * the segment's content and will cause an unspecified exception to be
1031 * thrown either at the time of the access or at some later time. It is
1032 * therefore strongly recommended that appropriate precautions be taken to
1033 * avoid the manipulation of a mapped file by this (or another) program,
1034 * except to read or write the file's content.
1035 *
1036 * @implNote When obtaining a mapped segment from a newly created file
1037 * channel, the initialization state of the contents of the block
1038 * of mapped memory associated with the returned mapped memory
1039 * segment is unspecified and should not be relied upon.
1040 *
1041 * @implSpec The default implementation of this method throws
1042 * {@code UnsupportedOperationException}.
1043 *
1044 * @param mode
1045 * The file mapping mode, see
1046 * {@link FileChannel#map(FileChannel.MapMode, long, long)};
1047 * the mapping mode might affect the behavior of the returned
1048 * memory mapped segment (see {@link MemorySegment#force()}).
1049 *
1050 * @param offset
1051 * The offset (expressed in bytes) within the file at which the
1052 * mapped segment is to start.
1053 *
1054 * @param size
1055 * The size (in bytes) of the mapped memory backing the memory
1056 * segment.
1057 *
1058 * @param arena
1059 * The segment arena.
1060 *
1061 * @return A new mapped memory segment.
1062 *
1063 * @throws IllegalArgumentException
1064 * If {@code offset < 0}, {@code size < 0} or
1065 * {@code offset + size} overflows the range of {@code long}.
1066 *
1067 * @throws IllegalStateException
1068 * If {@code arena.isAlive() == false}.
1069 *
1070 * @throws WrongThreadException
1071 * If {@code arena} is a confined scoped arena, and this method is called from a
1072 * thread {@code T}, other than the scoped arena's owner thread.
1073 *
1074 * @throws NonReadableChannelException
1075 * If the {@code mode} is {@link MapMode#READ_ONLY READ_ONLY} or
1076 * an implementation specific map mode requiring read access,
1077 * but this channel was not opened for reading.
1078 *
1079 * @throws NonWritableChannelException
1080 * If the {@code mode} is {@link MapMode#READ_WRITE READ_WRITE},
1081 * {@link MapMode#PRIVATE PRIVATE} or an implementation specific
1082 * map mode requiring write access, but this channel was not
1083 * opened for both reading and writing.
1084 *
1085 * @throws IOException
1086 * If some other I/O error occurs.
1087 *
1088 * @throws UnsupportedOperationException
1089 * If an unsupported map mode is specified.
1090 *
1091 * @since 22
1092 */
1093 public MemorySegment map(MapMode mode, long offset, long size, Arena arena)
1094 throws IOException
1095 {
1096 throw new UnsupportedOperationException();
1097 }
1098
1099 // -- Locks --
1100
1101 /**
1102 * Acquires a lock on the given region of this channel's file.
1103 *
1104 * <p> An invocation of this method will block until the region can be
1105 * locked, this channel is closed, or the invoking thread is interrupted,
1106 * whichever comes first.
1107 *
1108 * <p> If this channel is closed by another thread during an invocation of
1109 * this method then an {@link AsynchronousCloseException} will be thrown.
1110 *
1111 * <p> If the invoking thread is interrupted while waiting to acquire the
1112 * lock then its interrupt status will be set and a {@link
1113 * FileLockInterruptionException} will be thrown. If the invoker's
1114 * interrupt status is set when this method is invoked then that exception
1115 * will be thrown immediately; the thread's interrupt status will not be
1116 * changed.
1117 *
1118 * <p> The region specified by the {@code position} and {@code size}
1119 * parameters need not be contained within, or even overlap, the actual
1120 * underlying file. Lock regions are fixed in size; if a locked region
1121 * initially contains the end of the file and the file grows beyond the
1122 * region then the new portion of the file will not be covered by the lock.
1123 * If a file is expected to grow in size and a lock on the entire file is
1124 * required then a region starting at zero, and no smaller than the
1125 * expected maximum size of the file, should be locked. The zero-argument
1126 * {@link #lock()} method simply locks a region of size {@link
1127 * Long#MAX_VALUE}. If the {@code position} is non-negative and the
1128 * {@code size} is zero, then a lock of size
1129 * {@code Long.MAX_VALUE - position} is returned.
1130 *
1131 * <p> Some operating systems do not support shared locks, in which case a
1132 * request for a shared lock is automatically converted into a request for
1133 * an exclusive lock. Whether the newly-acquired lock is shared or
1134 * exclusive may be tested by invoking the resulting lock object's {@link
1135 * FileLock#isShared() isShared} method.
1136 *
1137 * <p> File locks are held on behalf of the entire Java virtual machine.
1138 * They are not suitable for controlling access to a file by multiple
1139 * threads within the same virtual machine. </p>
1140 *
1141 * @param position
1142 * The position at which the locked region is to start; must be
1143 * non-negative
1144 *
1145 * @param size
1146 * The size of the locked region; must be non-negative, and the sum
1147 * {@code position} + {@code size} must be non-negative.
1148 * A value of zero means to lock all bytes from the specified
1149 * starting position to the end of the file, regardless of whether
1150 * the file is subsequently extended or truncated
1151 *
1152 * @param shared
1153 * {@code true} to request a shared lock, in which case this
1154 * channel must be open for reading (and possibly writing);
1155 * {@code false} to request an exclusive lock, in which case this
1156 * channel must be open for writing (and possibly reading)
1157 *
1158 * @return A lock object representing the newly-acquired lock
1159 *
1160 * @throws IllegalArgumentException
1161 * If the preconditions on the parameters do not hold
1162 *
1163 * @throws ClosedChannelException
1164 * If this channel is closed
1165 *
1166 * @throws AsynchronousCloseException
1167 * If another thread closes this channel while the invoking
1168 * thread is blocked in this method
1169 *
1170 * @throws FileLockInterruptionException
1171 * If the invoking thread is interrupted while blocked in this
1172 * method
1173 *
1174 * @throws OverlappingFileLockException
1175 * If a lock that overlaps the requested region is already held by
1176 * this Java virtual machine, or if another thread is already
1177 * blocked in this method and is attempting to lock an overlapping
1178 * region
1179 *
1180 * @throws NonReadableChannelException
1181 * If {@code shared} is {@code true} but this channel was not
1182 * opened for reading
1183 *
1184 * @throws NonWritableChannelException
1185 * If {@code shared} is {@code false} but this channel was not
1186 * opened for writing
1187 *
1188 * @throws IOException
1189 * If some other I/O error occurs
1190 *
1191 * @see #lock()
1192 * @see #tryLock()
1193 * @see #tryLock(long,long,boolean)
1194 */
1195 public abstract FileLock lock(long position, long size, boolean shared)
1196 throws IOException;
1197
1198 /**
1199 * Acquires an exclusive lock on this channel's file.
1200 *
1201 * <p> An invocation of this method of the form {@code fc.lock()} behaves
1202 * in exactly the same way as the invocation
1203 *
1204 * {@snippet lang=java :
1205 * // @link substring="lock" target="#lock(long,long,boolean)" :
1206 * fc.lock(0L, Long.MAX_VALUE, false)
1207 * }
1208 *
1209 * @return A lock object representing the newly-acquired lock
1210 *
1211 * @throws ClosedChannelException
1212 * If this channel is closed
1213 *
1214 * @throws AsynchronousCloseException
1215 * If another thread closes this channel while the invoking
1216 * thread is blocked in this method
1217 *
1218 * @throws FileLockInterruptionException
1219 * If the invoking thread is interrupted while blocked in this
1220 * method
1221 *
1222 * @throws OverlappingFileLockException
1223 * If a lock that overlaps the requested region is already held by
1224 * this Java virtual machine, or if another thread is already
1225 * blocked in this method and is attempting to lock an overlapping
1226 * region of the same file
1227 *
1228 * @throws NonWritableChannelException
1229 * If this channel was not opened for writing
1230 *
1231 * @throws IOException
1232 * If some other I/O error occurs
1233 *
1234 * @see #lock(long,long,boolean)
1235 * @see #tryLock()
1236 * @see #tryLock(long,long,boolean)
1237 */
1238 public final FileLock lock() throws IOException {
1239 return lock(0L, Long.MAX_VALUE, false);
1240 }
1241
1242 /**
1243 * Attempts to acquire a lock on the given region of this channel's file.
1244 *
1245 * <p> This method does not block. An invocation always returns
1246 * immediately, either having acquired a lock on the requested region or
1247 * having failed to do so. If it fails to acquire a lock because an
1248 * overlapping lock is held by another program then it returns
1249 * {@code null}. If it fails to acquire a lock for any other reason then
1250 * an appropriate exception is thrown.
1251 *
1252 * <p> The region specified by the {@code position} and {@code size}
1253 * parameters need not be contained within, or even overlap, the actual
1254 * underlying file. Lock regions are fixed in size; if a locked region
1255 * initially contains the end of the file and the file grows beyond the
1256 * region then the new portion of the file will not be covered by the lock.
1257 * If a file is expected to grow in size and a lock on the entire file is
1258 * required then a region starting at zero, and no smaller than the
1259 * expected maximum size of the file, should be locked. The zero-argument
1260 * {@link #tryLock()} method simply locks a region of size {@link
1261 * Long#MAX_VALUE}. If the {@code position} is non-negative and the
1262 * {@code size} is zero, then a lock of size
1263 * {@code Long.MAX_VALUE - position} is returned.
1264 *
1265 * <p> Some operating systems do not support shared locks, in which case a
1266 * request for a shared lock is automatically converted into a request for
1267 * an exclusive lock. Whether the newly-acquired lock is shared or
1268 * exclusive may be tested by invoking the resulting lock object's {@link
1269 * FileLock#isShared() isShared} method.
1270 *
1271 * <p> File locks are held on behalf of the entire Java virtual machine.
1272 * They are not suitable for controlling access to a file by multiple
1273 * threads within the same virtual machine. </p>
1274 *
1275 * @param position
1276 * The position at which the locked region is to start; must be
1277 * non-negative
1278 *
1279 * @param size
1280 * The size of the locked region; must be non-negative, and the sum
1281 * {@code position} + {@code size} must be non-negative.
1282 * A value of zero means to lock all bytes from the specified
1283 * starting position to the end of the file, regardless of whether
1284 * the file is subsequently extended or truncated
1285 *
1286 * @param shared
1287 * {@code true} to request a shared lock,
1288 * {@code false} to request an exclusive lock
1289 *
1290 * @return A lock object representing the newly-acquired lock,
1291 * or {@code null} if the lock could not be acquired
1292 * because another program holds an overlapping lock
1293 *
1294 * @throws IllegalArgumentException
1295 * If the preconditions on the parameters do not hold
1296 *
1297 * @throws ClosedChannelException
1298 * If this channel is closed
1299 *
1300 * @throws OverlappingFileLockException
1301 * If a lock that overlaps the requested region is already held by
1302 * this Java virtual machine, or if another thread is already
1303 * blocked in this method and is attempting to lock an overlapping
1304 * region of the same file
1305 *
1306 * @throws NonReadableChannelException
1307 * If {@code shared} is {@code true} but this channel was not
1308 * opened for reading
1309 *
1310 * @throws NonWritableChannelException
1311 * If {@code shared} is {@code false} but this channel was not
1312 * opened for writing
1313 *
1314 * @throws IOException
1315 * If some other I/O error occurs
1316 *
1317 * @see #lock()
1318 * @see #lock(long,long,boolean)
1319 * @see #tryLock()
1320 */
1321 public abstract FileLock tryLock(long position, long size, boolean shared)
1322 throws IOException;
1323
1324 /**
1325 * Attempts to acquire an exclusive lock on this channel's file.
1326 *
1327 * <p> An invocation of this method of the form {@code fc.tryLock()}
1328 * behaves in exactly the same way as the invocation
1329 *
1330 * {@snippet lang=java :
1331 * // @link substring="tryLock" target="#tryLock(long,long,boolean)" :
1332 * fc.tryLock(0L, Long.MAX_VALUE, false)
1333 * }
1334 *
1335 * @return A lock object representing the newly-acquired lock,
1336 * or {@code null} if the lock could not be acquired
1337 * because another program holds an overlapping lock
1338 *
1339 * @throws ClosedChannelException
1340 * If this channel is closed
1341 *
1342 * @throws OverlappingFileLockException
1343 * If a lock that overlaps the requested region is already held by
1344 * this Java virtual machine, or if another thread is already
1345 * blocked in this method and is attempting to lock an overlapping
1346 * region
1347 *
1348 * @throws NonWritableChannelException
1349 * If this channel was not opened for writing
1350 *
1351 * @throws IOException
1352 * If some other I/O error occurs
1353 *
1354 * @see #lock()
1355 * @see #lock(long,long,boolean)
1356 * @see #tryLock(long,long,boolean)
1357 */
1358 public final FileLock tryLock() throws IOException {
1359 return tryLock(0L, Long.MAX_VALUE, false);
1360 }
1361
1362 }