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	/*
	* Copyright (c) 2007, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* 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).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.nio.channels;

	import java.nio.file.*;
	import java.nio.file.attribute.FileAttribute;
	import java.nio.file.spi.*;
	import java.nio.ByteBuffer;
	import java.io.IOException;
	import java.util.concurrent.Future;
	import java.util.concurrent.ExecutorService;
	import java.util.Set;
	import java.util.HashSet;
	import java.util.Collections;

	/**
	* An asynchronous channel for reading, writing, and manipulating a file.
	*
	* <p> An asynchronous file channel is created when a file is opened by invoking
	* one of the {@link #open open} methods defined by this class. The file contains
	* a variable-length sequence of bytes that can be read and written and whose
	* current size can be {@link #size() 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 truncated}.
	*
	* <p> An asynchronous file channel does not have a <i>current position</i>
	* within the file. Instead, the file position is specified to each read and
	* write method that initiates asynchronous operations. A {@link CompletionHandler}
	* is specified as a parameter and is invoked to consume the result of the I/O
	* operation. This class also defines read and write methods that initiate
	* asynchronous operations, returning a {@link Future} to represent the pending
	* result of the operation. The {@code Future} may be used to check if the
	* operation has completed, wait for its completion, and retrieve the result.
	*
	* <p> In addition to read and write operations, this class defines the
	* following operations: </p>
	*
	* <ul>
	*
	* <li><p> Updates made to a file may be {@link #force <i>forced
	* out</i>} to the underlying storage device, ensuring that data are not
	* lost in the event of a system crash. </p></li>
	*
	* <li><p> A region of a file may be {@link #lock <i>locked</i>} against
	* access by other programs. </p></li>
	*
	* </ul>
	*
	* <p> An {@code AsynchronousFileChannel} is associated with a thread pool to
	* which tasks are submitted to handle I/O events and dispatch to completion
	* handlers that consume the results of I/O operations on the channel. The
	* completion handler for an I/O operation initiated on a channel is guaranteed
	* to be invoked by one of the threads in the thread pool (This ensures that the
	* completion handler is run by a thread with the expected <em>identity</em>).
	* Where an I/O operation completes immediately, and the initiating thread is
	* itself a thread in the thread pool, then the completion handler may be invoked
	* directly by the initiating thread. When an {@code AsynchronousFileChannel} is
	* created without specifying a thread pool then the channel is associated with
	* a system-dependent default thread pool that may be shared with other
	* channels. The default thread pool is configured by the system properties
	* defined by the {@link AsynchronousChannelGroup} class.
	*
	* <p> Channels of this type 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. This causes all outstanding asynchronous
	* operations on the channel to complete with the exception {@link
	* AsynchronousCloseException}. Multiple read and write operations may be
	* outstanding at the same time. When multiple read and write operations are
	* outstanding then the ordering of the I/O operations, and the order that the
	* completion handlers are invoked, is not specified; they are not, in particular,
	* guaranteed to execute in the order that the operations were initiated. The
	* {@link java.nio.ByteBuffer ByteBuffers} used when reading or writing are not
	* safe for use by multiple concurrent I/O operations. Furthermore, after an I/O
	* operation is initiated then care should be taken to ensure that the buffer is
	* not accessed until after the operation has completed.
	*
	* <p> As with {@link FileChannel}, 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.
	*
	* @since 1.7
	*/

	public abstract class AsynchronousFileChannel
	implements AsynchronousChannel
	{
	/**
	* Initializes a new instance of this class.
	*/
	protected AsynchronousFileChannel() {
	}

	/**
	* Opens or creates a file for reading and/or writing, returning an
	* asynchronous file channel to access the file.
	*
	* <p> The {@code options} parameter determines how the file is opened.
	* The {@link StandardOpenOption#READ READ} and {@link StandardOpenOption#WRITE
	* WRITE} options determines if the file should be opened for reading and/or
	* writing. If neither option is contained in the array then an existing file
	* is opened for reading.
	*
	* <p> In addition to {@code READ} and {@code WRITE}, the following options
	* may be present:
	*
	* <table border=1 cellpadding=5 summary="">
	* <tr> <th>Option</th> <th>Description</th> </tr>
	* <tr>
	* <td> {@link StandardOpenOption#TRUNCATE_EXISTING TRUNCATE_EXISTING} </td>
	* <td> When opening an existing file, the file is first truncated to a
	* size of 0 bytes. This option is ignored when the file is opened only
	* for reading.</td>
	* </tr>
	* <tr>
	* <td> {@link StandardOpenOption#CREATE_NEW CREATE_NEW} </td>
	* <td> If this option is present then a new file is created, failing if
	* the file already exists. When creating a file the check for the
	* existence of the file and the creation of the file if it does not exist
	* is atomic with respect to other file system operations. This option is
	* ignored when the file is opened only for reading. </td>
	* </tr>
	* <tr>
	* <td > {@link StandardOpenOption#CREATE CREATE} </td>
	* <td> If this option is present then an existing file is opened if it
	* exists, otherwise a new file is created. When creating a file the check
	* for the existence of the file and the creation of the file if it does
	* not exist is atomic with respect to other file system operations. This
	* option is ignored if the {@code CREATE_NEW} option is also present or
	* the file is opened only for reading. </td>
	* </tr>
	* <tr>
	* <td > {@link StandardOpenOption#DELETE_ON_CLOSE DELETE_ON_CLOSE} </td>
	* <td> When this option is present then the implementation makes a
	* <em>best effort</em> attempt to delete the file when closed by the
	* the {@link #close close} method. If the {@code close} method is not
	* invoked then a <em>best effort</em> attempt is made to delete the file
	* when the Java virtual machine terminates. </td>
	* </tr>
	* <tr>
	* <td>{@link StandardOpenOption#SPARSE SPARSE} </td>
	* <td> When creating a new file this option is a <em>hint</em> that the
	* new file will be sparse. This option is ignored when not creating
	* a new file. </td>
	* </tr>
	* <tr>
	* <td> {@link StandardOpenOption#SYNC SYNC} </td>
	* <td> Requires that every update to the file's content or metadata be
	* written synchronously to the underlying storage device. (see <a
	* href="../file/package-summary.html#integrity"> Synchronized I/O file
	* integrity</a>). </td>
	* </tr>
	* <tr>
	* <td> {@link StandardOpenOption#DSYNC DSYNC} </td>
	* <td> Requires that every update to the file's content be written
	* synchronously to the underlying storage device. (see <a
	* href="../file/package-summary.html#integrity"> Synchronized I/O file
	* integrity</a>). </td>
	* </tr>
	* </table>
	*
	* <p> An implementation may also support additional options.
	*
	* <p> The {@code executor} parameter is the {@link ExecutorService} to
	* which tasks are submitted to handle I/O events and dispatch completion
	* results for operations initiated on resulting channel.
	* The nature of these tasks is highly implementation specific and so care
	* should be taken when configuring the {@code Executor}. Minimally it
	* should support an unbounded work queue and should not run tasks on the
	* caller thread of the {@link ExecutorService#execute execute} method.
	* Shutting down the executor service while the channel is open results in
	* unspecified behavior.
	*
	* <p> The {@code attrs} parameter is an optional array of file {@link
	* FileAttribute file-attributes} to set atomically when creating the file.
	*
	* <p> The new channel is created by invoking the {@link
	* FileSystemProvider#newFileChannel newFileChannel} method on the
	* provider that created the {@code Path}.
	*
	* @param file
	* The path of the file to open or create
	* @param options
	* Options specifying how the file is opened
	* @param executor
	* The thread pool or {@code null} to associate the channel with
	* the default thread pool
	* @param attrs
	* An optional list of file attributes to set atomically when
	* creating the file
	*
	* @return A new asynchronous file channel
	*
	* @throws IllegalArgumentException
	* If the set contains an invalid combination of options
	* @throws UnsupportedOperationException
	* If the {@code file} is associated with a provider that does not
	* support creating asynchronous file channels, or an unsupported
	* open option is specified, or the array contains an attribute that
	* cannot be set atomically when creating the file
	* @throws IOException
	* If an I/O error occurs
	* @throws SecurityException
	* If a security manager is installed and it denies an
	* unspecified permission required by the implementation.
	* In the case of the default provider, the {@link
	* SecurityManager#checkRead(String)} method is invoked to check
	* read access if the file is opened for reading. The {@link
	* SecurityManager#checkWrite(String)} method is invoked to check
	* write access if the file is opened for writing
	*/
	public static AsynchronousFileChannel open(Path file,
	Set<? extends OpenOption> options,
	ExecutorService executor,
	FileAttribute<?>... attrs)
	throws IOException
	{
	FileSystemProvider provider = file.getFileSystem().provider();
	return provider.newAsynchronousFileChannel(file, options, executor, attrs);
	}

	@SuppressWarnings({"unchecked", "rawtypes"}) // generic array construction
	private static final FileAttribute<?>[] NO_ATTRIBUTES = new FileAttribute[0];

	/**
	* Opens or creates a file for reading and/or writing, returning an
	* asynchronous file channel to access the file.
	*
	* <p> An invocation of this method behaves in exactly the same way as the
	* invocation
	* <pre>
	* ch.{@link #open(Path,Set,ExecutorService,FileAttribute[])
	* open}(file, opts, null, new FileAttribute<?>[0]);
	* </pre>
	* where {@code opts} is a {@code Set} containing the options specified to
	* this method.
	*
	* <p> The resulting channel is associated with default thread pool to which
	* tasks are submitted to handle I/O events and dispatch to completion
	* handlers that consume the result of asynchronous operations performed on
	* the resulting channel.
	*
	* @param file
	* The path of the file to open or create
	* @param options
	* Options specifying how the file is opened
	*
	* @return A new asynchronous file channel
	*
	* @throws IllegalArgumentException
	* If the set contains an invalid combination of options
	* @throws UnsupportedOperationException
	* If the {@code file} is associated with a provider that does not
	* support creating file channels, or an unsupported open option is
	* specified
	* @throws IOException
	* If an I/O error occurs
	* @throws SecurityException
	* If a security manager is installed and it denies an
	* unspecified permission required by the implementation.
	* In the case of the default provider, the {@link
	* SecurityManager#checkRead(String)} method is invoked to check
	* read access if the file is opened for reading. The {@link
	* SecurityManager#checkWrite(String)} method is invoked to check
	* write access if the file is opened for writing
	*/
	public static AsynchronousFileChannel open(Path file, OpenOption... options)
	throws IOException
	{
	Set<OpenOption> set = new HashSet<OpenOption>(options.length);
	Collections.addAll(set, options);
	return open(file, set, null, NO_ATTRIBUTES);
	}

	/**
	* Returns the current size of this channel's file.
	*
	* @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. </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 AsynchronousFileChannel 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 {@code metaData} parameter can be used to limit the number of
	* I/O operations that this method is required to perform. Passing
	* {@code false} for this parameter indicates that only updates to the
	* file's content need be written to storage; passing {@code true}
	* 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.
	*
	* @param metaData
	* If {@code true} 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;

	/**
	* Acquires a lock on the given region of this channel's file.
	*
	* <p> This method initiates an operation to acquire a lock on the given
	* region of this channel's file. The {@code handler} parameter is a
	* completion handler that is invoked when the lock is acquired (or the
	* operation fails). The result passed to the completion handler is the
	* resulting {@code FileLock}.
	*
	* <p> The region specified by the {@code position} and {@code size}
	* 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 two-argument
	* {@link #lock(Object,CompletionHandler)} method simply locks a region
	* of size {@link Long#MAX_VALUE}. If a lock that overlaps the requested
	* region is already held by this Java virtual machine, or this method has
	* been invoked to lock an overlapping region and that operation has not
	* completed, then this method throws {@link OverlappingFileLockException}.
	*
	* <p> Some operating systems do not support a mechanism to acquire a file
	* lock in an asynchronous manner. Consequently an implementation may
	* acquire the file lock in a background thread or from a task executed by
	* a thread in the associated thread pool. If there are many lock operations
	* outstanding then it may consume threads in the Java virtual machine for
	* indefinite periods.
	*
	* <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.
	*
	* @param <A>
	* The type of the attachment
	* @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
	* {@code position} + {@code size} must be non-negative
	* @param shared
	* {@code true} to request a shared lock, in which case this
	* channel must be open for reading (and possibly writing);
	* {@code false} to request an exclusive lock, in which case this
	* channel must be open for writing (and possibly reading)
	* @param attachment
	* The object to attach to the I/O operation; can be {@code null}
	* @param handler
	* The handler for consuming the result
	*
	* @throws OverlappingFileLockException
	* If a lock that overlaps the requested region is already held by
	* this Java virtual machine, or there is already a pending attempt
	* to lock an overlapping region
	* @throws IllegalArgumentException
	* If the preconditions on the parameters do not hold
	* @throws NonReadableChannelException
	* If {@code shared} is true but this channel was not opened for reading
	* @throws NonWritableChannelException
	* If {@code shared} is false but this channel was not opened for writing
	*/
	public abstract <A> void lock(long position,
	long size,
	boolean shared,
	A attachment,
	CompletionHandler<FileLock,? super A> handler);

	/**
	* Acquires an exclusive lock on this channel's file.
	*
	* <p> This method initiates an operation to acquire a lock on the given
	* region of this channel's file. The {@code handler} parameter is a
	* completion handler that is invoked when the lock is acquired (or the
	* operation fails). The result passed to the completion handler is the
	* resulting {@code FileLock}.
	*
	* <p> An invocation of this method of the form {@code ch.lock(att,handler)}
	* behaves in exactly the same way as the invocation
	* <pre>
	* ch.{@link #lock(long,long,boolean,Object,CompletionHandler) lock}(0L, Long.MAX_VALUE, false, att, handler)
	* </pre>
	*
	* @param <A>
	* The type of the attachment
	* @param attachment
	* The object to attach to the I/O operation; can be {@code null}
	* @param handler
	* The handler for consuming the result
	*
	* @throws OverlappingFileLockException
	* If a lock is already held by this Java virtual machine, or there
	* is already a pending attempt to lock a region
	* @throws NonWritableChannelException
	* If this channel was not opened for writing
	*/
	public final <A> void lock(A attachment,
	CompletionHandler<FileLock,? super A> handler)
	{
	lock(0L, Long.MAX_VALUE, false, attachment, handler);
	}

	/**
	* Acquires a lock on the given region of this channel's file.
	*
	* <p> This method initiates an operation to acquire a lock on the given
	* region of this channel's file. The method behaves in exactly the same
	* manner as the {@link #lock(long, long, boolean, Object, CompletionHandler)}
	* method except that instead of specifying a completion handler, this
	* method returns a {@code Future} representing the pending result. The
	* {@code Future}'s {@link Future#get() get} method returns the {@link
	* FileLock} on successful completion.
	*
	* @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
	* {@code position} + {@code size} must be non-negative
	* @param shared
	* {@code true} to request a shared lock, in which case this
	* channel must be open for reading (and possibly writing);
	* {@code false} to request an exclusive lock, in which case this
	* channel must be open for writing (and possibly reading)
	*
	* @return a {@code Future} object representing the pending result
	*
	* @throws OverlappingFileLockException
	* If a lock is already held by this Java virtual machine, or there
	* is already a pending attempt to lock a region
	* @throws IllegalArgumentException
	* If the preconditions on the parameters do not hold
	* @throws NonReadableChannelException
	* If {@code shared} is true but this channel was not opened for reading
	* @throws NonWritableChannelException
	* If {@code shared} is false but this channel was not opened for writing
	*/
	public abstract Future<FileLock> lock(long position, long size, boolean shared);

	/**
	* Acquires an exclusive lock on this channel's file.
	*
	* <p> This method initiates an operation to acquire an exclusive lock on this
	* channel's file. The method returns a {@code Future} representing the
	* pending result of the operation. The {@code Future}'s {@link Future#get()
	* get} method returns the {@link FileLock} on successful completion.
	*
	* <p> An invocation of this method behaves in exactly the same way as the
	* invocation
	* <pre>
	* ch.{@link #lock(long,long,boolean) lock}(0L, Long.MAX_VALUE, false)
	* </pre>
	*
	* @return a {@code Future} object representing the pending result
	*
	* @throws OverlappingFileLockException
	* If a lock is already held by this Java virtual machine, or there
	* is already a pending attempt to lock a region
	* @throws NonWritableChannelException
	* If this channel was not opened for writing
	*/
	public final Future<FileLock> lock() {
	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 {@code null}. If it fails to acquire
	* a lock for any other reason then an appropriate exception is thrown.
	*
	* @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
	* {@code position} + {@code size} must be non-negative
	*
	* @param shared
	* {@code true} to request a shared lock,
	* {@code false} to request an exclusive lock
	*
	* @return A lock object representing the newly-acquired lock,
	* or {@code null} 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 NonReadableChannelException
	* If {@code shared} is true but this channel was not opened for reading
	* @throws NonWritableChannelException
	* If {@code shared} is false but this channel was not opened for writing
	*
	* @throws IOException
	* If some other I/O error occurs
	*
	* @see #lock(Object,CompletionHandler)
	* @see #lock(long,long,boolean,Object,CompletionHandler)
	* @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 {@code ch.tryLock()}
	* behaves in exactly the same way as the invocation
	*
	* <pre>
	* ch.{@link #tryLock(long,long,boolean) tryLock}(0L, Long.MAX_VALUE, false) </pre>
	*
	* @return A lock object representing the newly-acquired lock,
	* or {@code null} 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 NonWritableChannelException
	* If {@code shared} is false but this channel was not opened for writing
	*
	* @throws IOException
	* If some other I/O error occurs
	*
	* @see #lock(Object,CompletionHandler)
	* @see #lock(long,long,boolean,Object,CompletionHandler)
	* @see #tryLock(long,long,boolean)
	*/
	public final FileLock tryLock() throws IOException {
	return tryLock(0L, Long.MAX_VALUE, false);
	}

	/**
	* Reads a sequence of bytes from this channel into the given buffer,
	* starting at the given file position.
	*
	* <p> This method initiates the reading of a sequence of bytes from this
	* channel into the given buffer, starting at the given file position. The
	* result of the read is the number of bytes read or {@code -1} if the given
	* position is greater than or equal to the file's size at the time that the
	* read is attempted.
	*
	* <p> This method works in the same manner as the {@link
	* AsynchronousByteChannel#read(ByteBuffer,Object,CompletionHandler)}
	* method, except that bytes are read starting at the given file position.
	* If the given file position is greater than the file's size at the time
	* that the read is attempted then no bytes are read.
	*
	* @param <A>
	* The type of the attachment
	* @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
	* @param attachment
	* The object to attach to the I/O operation; can be {@code null}
	* @param handler
	* The handler for consuming the result
	*
	* @throws IllegalArgumentException
	* If the position is negative or the buffer is read-only
	* @throws NonReadableChannelException
	* If this channel was not opened for reading
	*/
	public abstract <A> void read(ByteBuffer dst,
	long position,
	A attachment,
	CompletionHandler<Integer,? super A> handler);

	/**
	* Reads a sequence of bytes from this channel into the given buffer,
	* starting at the given file position.
	*
	* <p> This method initiates the reading of a sequence of bytes from this
	* channel into the given buffer, starting at the given file position. This
	* method returns a {@code Future} representing the pending result of the
	* operation. The {@code Future}'s {@link Future#get() get} method returns
	* the number of bytes read or {@code -1} if the given position is greater
	* than or equal to the file's size at the time that the read is attempted.
	*
	* <p> This method works in the same manner as the {@link
	* AsynchronousByteChannel#read(ByteBuffer)} method, except that bytes are
	* read starting at the given file position. If the given file position is
	* greater than the file's size at the time that the read is attempted then
	* no bytes are read.
	*
	* @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 A {@code Future} object representing the pending result
	*
	* @throws IllegalArgumentException
	* If the position is negative or the buffer is read-only
	* @throws NonReadableChannelException
	* If this channel was not opened for reading
	*/
	public abstract Future<Integer> read(ByteBuffer dst, long position);

	/**
	* 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
	* AsynchronousByteChannel#write(ByteBuffer,Object,CompletionHandler)}
	* method, except that bytes are written starting at the given file position.
	* If the given position is greater than the file's size, at the time that
	* the write is attempted, 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.
	*
	* @param <A>
	* The type of the attachment
	* @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
	* @param attachment
	* The object to attach to the I/O operation; can be {@code null}
	* @param handler
	* The handler for consuming the result
	*
	* @throws IllegalArgumentException
	* If the position is negative
	* @throws NonWritableChannelException
	* If this channel was not opened for writing
	*/
	public abstract <A> void write(ByteBuffer src,
	long position,
	A attachment,
	CompletionHandler<Integer,? super A> handler);

	/**
	* Writes a sequence of bytes to this channel from the given buffer, starting
	* at the given file position.
	*
	* <p> This method initiates the writing of a sequence of bytes to this
	* channel from the given buffer, starting at the given file position. The
	* method returns a {@code Future} representing the pending result of the
	* write operation. The {@code Future}'s {@link Future#get() get} method
	* returns the number of bytes written.
	*
	* <p> This method works in the same manner as the {@link
	* AsynchronousByteChannel#write(ByteBuffer)} method, except that bytes are
	* written starting at the given file position. If the given position is
	* greater than the file's size, at the time that the write is attempted,
	* 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.
	*
	* @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 A {@code Future} object representing the pending result
	*
	* @throws IllegalArgumentException
	* If the position is negative
	* @throws NonWritableChannelException
	* If this channel was not opened for writing
	*/
	public abstract Future<Integer> write(ByteBuffer src, long position);
	}

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