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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
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*
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package java.nio.channels;
import java.io.*;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.spi.AbstractInterruptibleChannel;
/**
* A channel for reading, writing, mapping, and manipulating a file.
*
* <p> A file channel has a current <i>position</i> within its file which can
* be both {@link #position() </code>queried<code>} and {@link #position(long)
* </code>modified<code>}. The file itself contains a variable-length sequence
* of bytes that can be read and written and whose current {@link #size
* </code><i>size</i><code>} can be queried. The size of the file increases
* when bytes are written beyond its current size; the size of the file
* decreases when it is {@link #truncate </code><i>truncated</i><code>}. The
* file may also have some associated <i>metadata</i> such as access
* permissions, content type, and last-modification time; this class does not
* define methods for metadata access.
*
* <p> In addition to the familiar read, write, and close operations of byte
* channels, this class defines the following file-specific operations: </p>
*
* <ul>
*
* <li><p> Bytes may be {@link #read(ByteBuffer, long) </code>read<code>} or
* {@link #write(ByteBuffer, long) </code>written<code>} at an absolute
* position in a file in a way that does not affect the channel's current
* position. </p></li>
*
* <li><p> A region of a file may be {@link #map </code>mapped<code>}
* directly into memory; for large files this is often much more efficient
* than invoking the usual <tt>read</tt> or <tt>write</tt> methods.
* </p></li>
*
* <li><p> Updates made to a file may be {@link #force </code>forced
* out<code>} to the underlying storage device, ensuring that data are not
* lost in the event of a system crash. </p></li>
*
* <li><p> Bytes can be transferred from a file {@link #transferTo </code>to
* some other channel<code>}, and {@link #transferFrom </code>vice
* versa<code>}, in a way that can be optimized by many operating systems
* into a very fast transfer directly to or from the filesystem cache.
* </p></li>
*
* <li><p> A region of a file may be {@link FileLock </code>locked<code>}
* against access by other programs. </p></li>
*
* </ul>
*
* <p> File channels are safe for use by multiple concurrent threads. The
* {@link Channel#close close} method may be invoked at any time, as specified
* by the {@link Channel} interface. Only one operation that involves the
* channel's position or can change its file's size may be in progress at any
* given time; attempts to initiate a second such operation while the first is
* still in progress will block until the first operation completes. Other
* operations, in particular those that take an explicit position, may proceed
* concurrently; whether they in fact do so is dependent upon the underlying
* implementation and is therefore unspecified.
*
* <p> The view of a file provided by an instance of this class is guaranteed
* to be consistent with other views of the same file provided by other
* instances in the same program. The view provided by an instance of this
* class may or may not, however, be consistent with the views seen by other
* concurrently-running programs due to caching performed by the underlying
* operating system and delays induced by network-filesystem protocols. This
* is true regardless of the language in which these other programs are
* written, and whether they are running on the same machine or on some other
* machine. The exact nature of any such inconsistencies are system-dependent
* and are therefore unspecified.
*
* <p> This class does not define methods for opening existing files or for
* creating new ones; such methods may be added in a future release. In this
* release a file channel can be obtained from an existing {@link
* java.io.FileInputStream#getChannel FileInputStream}, {@link
* java.io.FileOutputStream#getChannel FileOutputStream}, or {@link
* java.io.RandomAccessFile#getChannel RandomAccessFile} object by invoking
* that object's <tt>getChannel</tt> method, which returns a file channel that
* is connected to the same underlying file.
*
* <p> The state of a file channel is intimately connected to that of the
* object whose <tt>getChannel</tt> method returned the channel. Changing the
* channel's position, whether explicitly or by reading or writing bytes, will
* change the file position of the originating object, and vice versa.
* Changing the file's length via the file channel will change the length seen
* via the originating object, and vice versa. Changing the file's content by
* writing bytes will change the content seen by the originating object, and
* vice versa.
*
* <a name="open-mode"><p> At various points this class specifies that an
* instance that is "open for reading," "open for writing," or "open for
* reading and writing" is required. A channel obtained via the {@link
* java.io.FileInputStream#getChannel getChannel} method of a {@link
* java.io.FileInputStream} instance will be open for reading. A channel
* obtained via the {@link java.io.FileOutputStream#getChannel getChannel}
* method of a {@link java.io.FileOutputStream} instance will be open for
* writing. Finally, a channel obtained via the {@link
* java.io.RandomAccessFile#getChannel getChannel} method of a {@link
* java.io.RandomAccessFile} instance will be open for reading if the instance
* was created with mode <tt>"r"</tt> and will be open for reading and writing
* if the instance was created with mode <tt>"rw"</tt>.
*
* <a name="append-mode"><p> A file channel that is open for writing may be in
* <i>append mode</i>, for example if it was obtained from a file-output stream
* that was created by invoking the {@link
* java.io.FileOutputStream#FileOutputStream(java.io.File,boolean)
* FileOutputStream(File,boolean)} constructor and passing <tt>true</tt> for
* the second parameter. In this mode each invocation of a relative write
* operation first advances the position to the end of the file and then writes
* the requested data. Whether the advancement of the position and the writing
* of the data are done in a single atomic operation is system-dependent and
* therefore unspecified.
*
*
* @see java.io.FileInputStream#getChannel()
* @see java.io.FileOutputStream#getChannel()
* @see java.io.RandomAccessFile#getChannel()
*
* @author Mark Reinhold
* @author Mike McCloskey
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class FileChannel
extends AbstractInterruptibleChannel
implements ByteChannel, GatheringByteChannel, ScatteringByteChannel
{
/**
* Initializes a new instance of this class.
*/
protected FileChannel() { }
// -- Channel operations --
/**
* Reads a sequence of bytes from this channel into the given buffer.
*
* <p> Bytes are read starting at this channel's current file position, and
* then the file position is updated with the number of bytes actually
* read. Otherwise this method behaves exactly as specified in the {@link
* ReadableByteChannel} interface. </p>
*/
public abstract int read(ByteBuffer dst) throws IOException;
/**
* Reads a sequence of bytes from this channel into a subsequence of the
* given buffers.
*
* <p> Bytes are read starting at this channel's current file position, and
* then the file position is updated with the number of bytes actually
* read. Otherwise this method behaves exactly as specified in the {@link
* ScatteringByteChannel} interface. </p>
*/
public abstract long read(ByteBuffer[] dsts, int offset, int length)
throws IOException;
/**
* Reads a sequence of bytes from this channel into the given buffers.
*
* <p> Bytes are read starting at this channel's current file position, and
* then the file position is updated with the number of bytes actually
* read. Otherwise this method behaves exactly as specified in the {@link
* ScatteringByteChannel} interface. </p>
*/
public final long read(ByteBuffer[] dsts) throws IOException {
return read(dsts, 0, dsts.length);
}
/**
* Writes a sequence of bytes to this channel from the given buffer.
*
* <p> Bytes are written starting at this channel's current file position
* unless the channel is in append mode, in which case the position is
* first advanced to the end of the file. The file is grown, if necessary,
* to accommodate the written bytes, and then the file position is updated
* with the number of bytes actually written. Otherwise this method
* behaves exactly as specified by the {@link WritableByteChannel}
* interface. </p>
*/
public abstract int write(ByteBuffer src) throws IOException;
/**
* Writes a sequence of bytes to this channel from a subsequence of the
* given buffers.
*
* <p> Bytes are written starting at this channel's current file position
* unless the channel is in append mode, in which case the position is
* first advanced to the end of the file. The file is grown, if necessary,
* to accommodate the written bytes, and then the file position is updated
* with the number of bytes actually written. Otherwise this method
* behaves exactly as specified in the {@link GatheringByteChannel}
* interface. </p>
*/
public abstract long write(ByteBuffer[] srcs, int offset, int length)
throws IOException;
/**
* Writes a sequence of bytes to this channel from the given buffers.
*
* <p> Bytes are written starting at this channel's current file position
* unless the channel is in append mode, in which case the position is
* first advanced to the end of the file. The file is grown, if necessary,
* to accommodate the written bytes, and then the file position is updated
* with the number of bytes actually written. Otherwise this method
* behaves exactly as specified in the {@link GatheringByteChannel}
* interface. </p>
*/
public final long write(ByteBuffer[] srcs) throws IOException {
return write(srcs, 0, srcs.length);
}
// -- Other operations --
/**
* Returns this channel's file position. </p>
*
* @return This channel's file position,
* a non-negative integer counting the number of bytes
* from the beginning of the file to the current position
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract long position() throws IOException;
/**
* Sets this channel's file position.
*
* <p> Setting the position to a value that is greater than the file's
* current size is legal but does not change the size of the file. A later
* attempt to read bytes at such a position will immediately return an
* end-of-file indication. A later attempt to write bytes at such a
* position will cause the file to be grown to accommodate the new bytes;
* the values of any bytes between the previous end-of-file and the
* newly-written bytes are unspecified. </p>
*
* @param newPosition
* The new position, a non-negative integer counting
* the number of bytes from the beginning of the file
*
* @return This file channel
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IllegalArgumentException
* If the new position is negative
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract FileChannel position(long newPosition) throws IOException;
/**
* Returns the current size of this channel's file. </p>
*
* @return The current size of this channel's file,
* measured in bytes
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract long size() throws IOException;
/**
* Truncates this channel's file to the given size.
*
* <p> If the given size is less than the file's current size then the file
* is truncated, discarding any bytes beyond the new end of the file. If
* the given size is greater than or equal to the file's current size then
* the file is not modified. In either case, if this channel's file
* position is greater than the given size then it is set to that size.
* </p>
*
* @param size
* The new size, a non-negative byte count
*
* @return This file channel
*
* @throws NonWritableChannelException
* If this channel was not opened for writing
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IllegalArgumentException
* If the new size is negative
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract FileChannel truncate(long size) throws IOException;
/**
* Forces any updates to this channel's file to be written to the storage
* device that contains it.
*
* <p> If this channel's file resides on a local storage device then when
* this method returns it is guaranteed that all changes made to the file
* since this channel was created, or since this method was last invoked,
* will have been written to that device. This is useful for ensuring that
* critical information is not lost in the event of a system crash.
*
* <p> If the file does not reside on a local device then no such guarantee
* is made.
*
* <p> The <tt>metaData</tt> parameter can be used to limit the number of
* I/O operations that this method is required to perform. Passing
* <tt>false</tt> for this parameter indicates that only updates to the
* file's content need be written to storage; passing <tt>true</tt>
* indicates that updates to both the file's content and metadata must be
* written, which generally requires at least one more I/O operation.
* Whether this parameter actually has any effect is dependent upon the
* underlying operating system and is therefore unspecified.
*
* <p> Invoking this method may cause an I/O operation to occur even if the
* channel was only opened for reading. Some operating systems, for
* example, maintain a last-access time as part of a file's metadata, and
* this time is updated whenever the file is read. Whether or not this is
* actually done is system-dependent and is therefore unspecified.
*
* <p> This method is only guaranteed to force changes that were made to
* this channel's file via the methods defined in this class. It may or
* may not force changes that were made by modifying the content of a
* {@link MappedByteBuffer </code>mapped byte buffer<code>} obtained by
* invoking the {@link #map map} method. Invoking the {@link
* MappedByteBuffer#force force} method of the mapped byte buffer will
* force changes made to the buffer's content to be written. </p>
*
* @param metaData
* If <tt>true</tt> then this method is required to force changes
* to both the file's content and metadata to be written to
* storage; otherwise, it need only force content changes to be
* written
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract void force(boolean metaData) throws IOException;
/**
* Transfers bytes from this channel's file to the given writable byte
* channel.
*
* <p> An attempt is made to read up to <tt>count</tt> bytes starting at
* the given <tt>position</tt> in this channel's file and write them to the
* target channel. An invocation of this method may or may not transfer
* all of the requested bytes; whether or not it does so depends upon the
* natures and states of the channels. Fewer than the requested number of
* bytes are transferred if this channel's file contains fewer than
* <tt>count</tt> bytes starting at the given <tt>position</tt>, or if the
* target channel is non-blocking and it has fewer than <tt>count</tt>
* bytes free in its output buffer.
*
* <p> This method does not modify this channel's position. If the given
* position is greater than the file's current size then no bytes are
* transferred. If the target channel has a position then bytes are
* written starting at that position and then the position is incremented
* by the number of bytes written.
*
* <p> This method is potentially much more efficient than a simple loop
* that reads from this channel and writes to the target channel. Many
* operating systems can transfer bytes directly from the filesystem cache
* to the target channel without actually copying them. </p>
*
* @param position
* The position within the file at which the transfer is to begin;
* must be non-negative
*
* @param count
* The maximum number of bytes to be transferred; must be
* non-negative
*
* @param target
* The target channel
*
* @return The number of bytes, possibly zero,
* that were actually transferred
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
*
* @throws NonReadableChannelException
* If this channel was not opened for reading
*
* @throws NonWritableChannelException
* If the target channel was not opened for writing
*
* @throws ClosedChannelException
* If either this channel or the target channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes either channel
* while the transfer is in progress
*
* @throws ClosedByInterruptException
* If another thread interrupts the current thread while the
* transfer is in progress, thereby closing both channels and
* setting the current thread's interrupt status
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract long transferTo(long position, long count,
WritableByteChannel target)
throws IOException;
/**
* Transfers bytes into this channel's file from the given readable byte
* channel.
*
* <p> An attempt is made to read up to <tt>count</tt> bytes from the
* source channel and write them to this channel's file starting at the
* given <tt>position</tt>. An invocation of this method may or may not
* transfer all of the requested bytes; whether or not it does so depends
* upon the natures and states of the channels. Fewer than the requested
* number of bytes will be transferred if the source channel has fewer than
* <tt>count</tt> bytes remaining, or if the source channel is non-blocking
* and has fewer than <tt>count</tt> bytes immediately available in its
* input buffer.
*
* <p> This method does not modify this channel's position. If the given
* position is greater than the file's current size then no bytes are
* transferred. If the source channel has a position then bytes are read
* starting at that position and then the position is incremented by the
* number of bytes read.
*
* <p> This method is potentially much more efficient than a simple loop
* that reads from the source channel and writes to this channel. Many
* operating systems can transfer bytes directly from the source channel
* into the filesystem cache without actually copying them. </p>
*
* @param src
* The source channel
*
* @param position
* The position within the file at which the transfer is to begin;
* must be non-negative
*
* @param count
* The maximum number of bytes to be transferred; must be
* non-negative
*
* @return The number of bytes, possibly zero,
* that were actually transferred
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
*
* @throws NonReadableChannelException
* If the source channel was not opened for reading
*
* @throws NonWritableChannelException
* If this channel was not opened for writing
*
* @throws ClosedChannelException
* If either this channel or the source channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes either channel
* while the transfer is in progress
*
* @throws ClosedByInterruptException
* If another thread interrupts the current thread while the
* transfer is in progress, thereby closing both channels and
* setting the current thread's interrupt status
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract long transferFrom(ReadableByteChannel src,
long position, long count)
throws IOException;
/**
* Reads a sequence of bytes from this channel into the given buffer,
* starting at the given file position.
*
* <p> This method works in the same manner as the {@link
* #read(ByteBuffer)} method, except that bytes are read starting at the
* given file position rather than at the channel's current position. This
* method does not modify this channel's position. If the given position
* is greater than the file's current size then no bytes are read. </p>
*
* @param dst
* The buffer into which bytes are to be transferred
*
* @param position
* The file position at which the transfer is to begin;
* must be non-negative
*
* @return The number of bytes read, possibly zero, or <tt>-1</tt> if the
* given position is greater than or equal to the file's current
* size
*
* @throws IllegalArgumentException
* If the position is negative
*
* @throws NonReadableChannelException
* If this channel was not opened for reading
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes this channel
* while the read operation is in progress
*
* @throws ClosedByInterruptException
* If another thread interrupts the current thread
* while the read operation is in progress, thereby
* closing the channel and setting the current thread's
* interrupt status
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract int read(ByteBuffer dst, long position) throws IOException;
/**
* Writes a sequence of bytes to this channel from the given buffer,
* starting at the given file position.
*
* <p> This method works in the same manner as the {@link
* #write(ByteBuffer)} method, except that bytes are written starting at
* the given file position rather than at the channel's current position.
* This method does not modify this channel's position. If the given
* position is greater than the file's current size then the file will be
* grown to accommodate the new bytes; the values of any bytes between the
* previous end-of-file and the newly-written bytes are unspecified. </p>
*
* @param src
* The buffer from which bytes are to be transferred
*
* @param position
* The file position at which the transfer is to begin;
* must be non-negative
*
* @return The number of bytes written, possibly zero
*
* @throws IllegalArgumentException
* If the position is negative
*
* @throws NonWritableChannelException
* If this channel was not opened for writing
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes this channel
* while the write operation is in progress
*
* @throws ClosedByInterruptException
* If another thread interrupts the current thread
* while the write operation is in progress, thereby
* closing the channel and setting the current thread's
* interrupt status
*
* @throws IOException
* If some other I/O error occurs
*/
public abstract int write(ByteBuffer src, long position) throws IOException;
// -- Memory-mapped buffers --
/**
* A typesafe enumeration for file-mapping modes.
*
* @since 1.4
*
* @see java.nio.channels.FileChannel#map
*/
public static class MapMode {
/**
* Mode for a read-only mapping.
*/
public static final MapMode READ_ONLY
= new MapMode("READ_ONLY");
/**
* Mode for a read/write mapping.
*/
public static final MapMode READ_WRITE
= new MapMode("READ_WRITE");
/**
* Mode for a private (copy-on-write) mapping.
*/
public static final MapMode PRIVATE
= new MapMode("PRIVATE");
private final String name;
private MapMode(String name) {
this.name = name;
}
/**
* Returns a string describing this file-mapping mode.
*
* @return A descriptive string
*/
public String toString() {
return name;
}
}
/**
* Maps a region of this channel's file directly into memory.
*
* <p> A region of a file may be mapped into memory in one of three modes:
* </p>
*
* <ul type=disc>
*
* <li><p> <i>Read-only:</i> Any attempt to modify the resulting buffer
* will cause a {@link java.nio.ReadOnlyBufferException} to be thrown.
* ({@link MapMode#READ_ONLY MapMode.READ_ONLY}) </p></li>
*
* <li><p> <i>Read/write:</i> Changes made to the resulting buffer will
* eventually be propagated to the file; they may or may not be made
* visible to other programs that have mapped the same file. ({@link
* MapMode#READ_WRITE MapMode.READ_WRITE}) </p></li>
*
* <li><p> <i>Private:</i> Changes made to the resulting buffer will not
* be propagated to the file and will not be visible to other programs
* that have mapped the same file; instead, they will cause private
* copies of the modified portions of the buffer to be created. ({@link
* MapMode#PRIVATE MapMode.PRIVATE}) </p></li>
*
* </ul>
*
* <p> For a read-only mapping, this channel must have been opened for
* reading; for a read/write or private mapping, this channel must have
* been opened for both reading and writing.
*
* <p> The {@link MappedByteBuffer </code>mapped byte buffer<code>}
* returned by this method will have a position of zero and a limit and
* capacity of <tt>size</tt>; its mark will be undefined. The buffer and
* the mapping that it represents will remain valid until the buffer itself
* is garbage-collected.
*
* <p> A mapping, once established, is not dependent upon the file channel
* that was used to create it. Closing the channel, in particular, has no
* effect upon the validity of the mapping.
*
* <p> Many of the details of memory-mapped files are inherently dependent
* upon the underlying operating system and are therefore unspecified. The
* behavior of this method when the requested region is not completely
* contained within this channel's file is unspecified. Whether changes
* made to the content or size of the underlying file, by this program or
* another, are propagated to the buffer is unspecified. The rate at which
* changes to the buffer are propagated to the file is unspecified.
*
* <p> For most operating systems, mapping a file into memory is more
* expensive than reading or writing a few tens of kilobytes of data via
* the usual {@link #read read} and {@link #write write} methods. From the
* standpoint of performance it is generally only worth mapping relatively
* large files into memory. </p>
*
* @param mode
* One of the constants {@link MapMode#READ_ONLY READ_ONLY}, {@link
* MapMode#READ_WRITE READ_WRITE}, or {@link MapMode#PRIVATE
* PRIVATE} defined in the {@link MapMode} class, according to
* whether the file is to be mapped read-only, read/write, or
* privately (copy-on-write), respectively
*
* @param position
* The position within the file at which the mapped region
* is to start; must be non-negative
*
* @param size
* The size of the region to be mapped; must be non-negative and
* no greater than {@link java.lang.Integer#MAX_VALUE}
*
* @throws NonReadableChannelException
* If the <tt>mode</tt> is {@link MapMode#READ_ONLY READ_ONLY} but
* this channel was not opened for reading
*
* @throws NonWritableChannelException
* If the <tt>mode</tt> is {@link MapMode#READ_WRITE READ_WRITE} or
* {@link MapMode#PRIVATE PRIVATE} but this channel was not opened
* for both reading and writing
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
*
* @throws IOException
* If some other I/O error occurs
*
* @see java.nio.channels.FileChannel.MapMode
* @see java.nio.MappedByteBuffer
*/
public abstract MappedByteBuffer map(MapMode mode,
long position, long size)
throws IOException;
// -- Locks --
/**
* Acquires a lock on the given region of this channel's file.
*
* <p> An invocation of this method will block until the region can be
* locked, this channel is closed, or the invoking thread is interrupted,
* whichever comes first.
*
* <p> If this channel is closed by another thread during an invocation of
* this method then an {@link AsynchronousCloseException} will be thrown.
*
* <p> If the invoking thread is interrupted while waiting to acquire the
* lock then its interrupt status will be set and a {@link
* FileLockInterruptionException} will be thrown. If the invoker's
* interrupt status is set when this method is invoked then that exception
* will be thrown immediately; the thread's interrupt status will not be
* changed.
*
* <p> The region specified by the <tt>position</tt> and <tt>size</tt>
* parameters need not be contained within, or even overlap, the actual
* underlying file. Lock regions are fixed in size; if a locked region
* initially contains the end of the file and the file grows beyond the
* region then the new portion of the file will not be covered by the lock.
* If a file is expected to grow in size and a lock on the entire file is
* required then a region starting at zero, and no smaller than the
* expected maximum size of the file, should be locked. The zero-argument
* {@link #lock()} method simply locks a region of size {@link
* Long#MAX_VALUE}.
*
* <p> Some operating systems do not support shared locks, in which case a
* request for a shared lock is automatically converted into a request for
* an exclusive lock. Whether the newly-acquired lock is shared or
* exclusive may be tested by invoking the resulting lock object's {@link
* FileLock#isShared() isShared} method.
*
* <p> File locks are held on behalf of the entire Java virtual machine.
* They are not suitable for controlling access to a file by multiple
* threads within the same virtual machine. </p>
*
* @param position
* The position at which the locked region is to start; must be
* non-negative
*
* @param size
* The size of the locked region; must be non-negative, and the sum
* <tt>position</tt> + <tt>size</tt> must be non-negative
*
* @param shared
* <tt>true</tt> to request a shared lock, in which case this
* channel must be open for reading (and possibly writing);
* <tt>false</tt> to request an exclusive lock, in which case this
* channel must be open for writing (and possibly reading)
*
* @return A lock object representing the newly-acquired lock
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes this channel while the invoking
* thread is blocked in this method
*
* @throws FileLockInterruptionException
* If the invoking thread is interrupted while blocked in this
* method
*
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region
*
* @throws NonReadableChannelException
* If <tt>shared</tt> is <tt>true</tt> this channel was not
* opened for reading
*
* @throws NonWritableChannelException
* If <tt>shared</tt> is <tt>false</tt> but this channel was not
* opened for writing
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock()
* @see #tryLock()
* @see #tryLock(long,long,boolean)
*/
public abstract FileLock lock(long position, long size, boolean shared)
throws IOException;
/**
* Acquires an exclusive lock on this channel's file.
*
* <p> An invocation of this method of the form <tt>fc.lock()</tt> behaves
* in exactly the same way as the invocation
*
* <pre>
* fc.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false) </pre>
*
* @return A lock object representing the newly-acquired lock
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws AsynchronousCloseException
* If another thread closes this channel while the invoking
* thread is blocked in this method
*
* @throws FileLockInterruptionException
* If the invoking thread is interrupted while blocked in this
* method
*
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region of the same file
*
* @throws NonWritableChannelException
* If this channel was not opened for writing
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock(long,long,boolean)
* @see #tryLock()
* @see #tryLock(long,long,boolean)
*/
public final FileLock lock() throws IOException {
return lock(0L, Long.MAX_VALUE, false);
}
/**
* Attempts to acquire a lock on the given region of this channel's file.
*
* <p> This method does not block. An invocation always returns
* immediately, either having acquired a lock on the requested region or
* having failed to do so. If it fails to acquire a lock because an
* overlapping lock is held by another program then it returns
* <tt>null</tt>. If it fails to acquire a lock for any other reason then
* an appropriate exception is thrown.
*
* <p> The region specified by the <tt>position</tt> and <tt>size</tt>
* parameters need not be contained within, or even overlap, the actual
* underlying file. Lock regions are fixed in size; if a locked region
* initially contains the end of the file and the file grows beyond the
* region then the new portion of the file will not be covered by the lock.
* If a file is expected to grow in size and a lock on the entire file is
* required then a region starting at zero, and no smaller than the
* expected maximum size of the file, should be locked. The zero-argument
* {@link #tryLock()} method simply locks a region of size {@link
* Long#MAX_VALUE}.
*
* <p> Some operating systems do not support shared locks, in which case a
* request for a shared lock is automatically converted into a request for
* an exclusive lock. Whether the newly-acquired lock is shared or
* exclusive may be tested by invoking the resulting lock object's {@link
* FileLock#isShared() isShared} method.
*
* <p> File locks are held on behalf of the entire Java virtual machine.
* They are not suitable for controlling access to a file by multiple
* threads within the same virtual machine. </p>
*
* @param position
* The position at which the locked region is to start; must be
* non-negative
*
* @param size
* The size of the locked region; must be non-negative, and the sum
* <tt>position</tt> + <tt>size</tt> must be non-negative
*
* @param shared
* <tt>true</tt> to request a shared lock,
* <tt>false</tt> to request an exclusive lock
*
* @return A lock object representing the newly-acquired lock,
* or <tt>null</tt> if the lock could not be acquired
* because another program holds an overlapping lock
*
* @throws IllegalArgumentException
* If the preconditions on the parameters do not hold
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region of the same file
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock()
* @see #lock(long,long,boolean)
* @see #tryLock()
*/
public abstract FileLock tryLock(long position, long size, boolean shared)
throws IOException;
/**
* Attempts to acquire an exclusive lock on this channel's file.
*
* <p> An invocation of this method of the form <tt>fc.tryLock()</tt>
* behaves in exactly the same way as the invocation
*
* <pre>
* fc.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
*
* @return A lock object representing the newly-acquired lock,
* or <tt>null</tt> if the lock could not be acquired
* because another program holds an overlapping lock
*
* @throws ClosedChannelException
* If this channel is closed
*
* @throws OverlappingFileLockException
* If a lock that overlaps the requested region is already held by
* this Java virtual machine, or if another thread is already
* blocked in this method and is attempting to lock an overlapping
* region
*
* @throws IOException
* If some other I/O error occurs
*
* @see #lock()
* @see #lock(long,long,boolean)
* @see #tryLock(long,long,boolean)
*/
public final FileLock tryLock() throws IOException {
return tryLock(0L, Long.MAX_VALUE, false);
}
}