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	/*
	* Copyright (c) 2000, 2021, 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;

	import java.io.FileDescriptor;
	import java.io.UncheckedIOException;
	import java.lang.ref.Reference;
	import java.util.Objects;

	import jdk.internal.access.foreign.MemorySegmentProxy;
	import jdk.internal.access.foreign.UnmapperProxy;
	import jdk.internal.misc.ScopedMemoryAccess;
	import jdk.internal.misc.Unsafe;


	/**
	* A direct byte buffer whose content is a memory-mapped region of a file.
	*
	* <p> Mapped byte buffers are created via the {@link
	* java.nio.channels.FileChannel#map FileChannel.map} method. This class
	* extends the {@link ByteBuffer} class with operations that are specific to
	* memory-mapped file regions.
	*
	* <p> A mapped byte buffer and the file mapping that it represents remain
	* valid until the buffer itself is garbage-collected.
	*
	* <p> The content of a mapped byte buffer can change at any time, for example
	* if the content of the corresponding region of the mapped file is changed by
	* this program or another. Whether or not such changes occur, and when they
	* occur, is operating-system dependent and therefore unspecified.
	*
	* <a id="inaccess"></a><p> All or part of a mapped byte buffer may become
	* inaccessible at any time, for example if the mapped file is truncated. An
	* attempt to access an inaccessible region of a mapped byte buffer will not
	* change the buffer's content and will cause an unspecified exception to be
	* thrown either at the time of the access or at some later time. It is
	* therefore strongly recommended that appropriate precautions be taken to
	* avoid the manipulation of a mapped file by this program, or by a
	* concurrently running program, except to read or write the file's content.
	*
	* <p> Mapped byte buffers otherwise behave no differently than ordinary direct
	* byte buffers. </p>
	*
	*
	* @author Mark Reinhold
	* @author JSR-51 Expert Group
	* @since 1.4
	*/

	public abstract class MappedByteBuffer
	extends ByteBuffer
	{

	// This is a little bit backwards: By rights MappedByteBuffer should be a
	// subclass of DirectByteBuffer, but to keep the spec clear and simple, and
	// for optimization purposes, it's easier to do it the other way around.
	// This works because DirectByteBuffer is a package-private class.

	// For mapped buffers, a FileDescriptor that may be used for mapping
	// operations if valid; null if the buffer is not mapped.
	private final FileDescriptor fd;

	// A flag true if this buffer is mapped against non-volatile
	// memory using one of the extended FileChannel.MapMode modes,
	// MapMode.READ_ONLY_SYNC or MapMode.READ_WRITE_SYNC and false if
	// it is mapped using any of the other modes. This flag only
	// determines the behavior of force operations.
	private final boolean isSync;

	static final ScopedMemoryAccess SCOPED_MEMORY_ACCESS = ScopedMemoryAccess.getScopedMemoryAccess();

	// This should only be invoked by the DirectByteBuffer constructors
	//
	MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private
	FileDescriptor fd, boolean isSync, MemorySegmentProxy segment) {
	super(mark, pos, lim, cap, segment);
	this.fd = fd;
	this.isSync = isSync;
	}

	MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private
	boolean isSync, MemorySegmentProxy segment) {
	super(mark, pos, lim, cap, segment);
	this.fd = null;
	this.isSync = isSync;
	}

	MappedByteBuffer(int mark, int pos, int lim, int cap, MemorySegmentProxy segment) { // package-private
	super(mark, pos, lim, cap, segment);
	this.fd = null;
	this.isSync = false;
	}

	UnmapperProxy unmapper() {
	return fd != null ?
	new UnmapperProxy() {
	@Override
	public long address() {
	return address;
	}

	@Override
	public FileDescriptor fileDescriptor() {
	return fd;
	}

	@Override
	public boolean isSync() {
	return isSync;
	}

	@Override
	public void unmap() {
	Unsafe.getUnsafe().invokeCleaner(MappedByteBuffer.this);
	}
	} : null;
	}

	/**
	* Tells whether this buffer was mapped against a non-volatile
	* memory device by passing one of the sync map modes {@link
	* jdk.nio.mapmode.ExtendedMapMode#READ_ONLY_SYNC
	* ExtendedMapModeMapMode#READ_ONLY_SYNC} or {@link
	* jdk.nio.mapmode.ExtendedMapMode#READ_ONLY_SYNC
	* ExtendedMapMode#READ_WRITE_SYNC} in the call to {@link
	* java.nio.channels.FileChannel#map FileChannel.map} or was
	* mapped by passing one of the other map modes.
	*
	* @return true if the file was mapped using one of the sync map
	* modes, otherwise false.
	*/
	final boolean isSync() { // package-private
	return isSync;
	}

	/**
	* Returns the {@code FileDescriptor} associated with this
	* {@code MappedByteBuffer}.
	*
	* @return the buffer's file descriptor; may be {@code null}
	*/
	final FileDescriptor fileDescriptor() { // package-private
	return fd;
	}

	/**
	* Tells whether or not this buffer's content is resident in physical
	* memory.
	*
	* <p> A return value of {@code true} implies that it is highly likely
	* that all of the data in this buffer is resident in physical memory and
	* may therefore be accessed without incurring any virtual-memory page
	* faults or I/O operations. A return value of {@code false} does not
	* necessarily imply that the buffer's content is not resident in physical
	* memory.
	*
	* <p> The returned value is a hint, rather than a guarantee, because the
	* underlying operating system may have paged out some of the buffer's data
	* by the time that an invocation of this method returns. </p>
	*
	* @return {@code true} if it is likely that this buffer's content
	* is resident in physical memory
	*/
	public final boolean isLoaded() {
	if (fd == null) {
	return true;
	}
	return SCOPED_MEMORY_ACCESS.isLoaded(scope(), address, isSync, capacity());
	}

	/**
	* Loads this buffer's content into physical memory.
	*
	* <p> This method makes a best effort to ensure that, when it returns,
	* this buffer's content is resident in physical memory. Invoking this
	* method may cause some number of page faults and I/O operations to
	* occur. </p>
	*
	* @return This buffer
	*/
	public final MappedByteBuffer load() {
	if (fd == null) {
	return this;
	}
	try {
	SCOPED_MEMORY_ACCESS.load(scope(), address, isSync, capacity());
	} finally {
	Reference.reachabilityFence(this);
	}
	return this;
	}

	/**
	* Forces any changes made to this buffer's content to be written to the
	* storage device containing the mapped file. The region starts at index
	* zero in this buffer and is {@code capacity()} bytes. An invocation of
	* this method behaves in exactly the same way as the invocation
	* {@link force(int,int) force(0,capacity())}.
	*
	* <p> If the file mapped into this buffer resides on a local storage
	* device then when this method returns it is guaranteed that all changes
	* made to the buffer since it was created, or since this method was last
	* invoked, will have been written to that device.
	*
	* <p> If the file does not reside on a local device then no such guarantee
	* is made.
	*
	* <p> If this buffer was not mapped in read/write mode ({@link
	* java.nio.channels.FileChannel.MapMode#READ_WRITE}) then
	* invoking this method may have no effect. In particular, the
	* method has no effect for buffers mapped in read-only or private
	* mapping modes. This method may or may not have an effect for
	* implementation-specific mapping modes. </p>
	*
	* @throws UncheckedIOException
	* If an I/O error occurs writing the buffer's content to the
	* storage device containing the mapped file
	*
	* @return This buffer
	*/
	public final MappedByteBuffer force() {
	if (fd == null) {
	return this;
	}
	int capacity = capacity();
	if (isSync \|\| ((address != 0) && (capacity != 0))) {
	return force(0, capacity);
	}
	return this;
	}

	/**
	* Forces any changes made to a region of this buffer's content to
	* be written to the storage device containing the mapped
	* file. The region starts at the given {@code index} in this
	* buffer and is {@code length} bytes.
	*
	* <p> If the file mapped into this buffer resides on a local
	* storage device then when this method returns it is guaranteed
	* that all changes made to the selected region buffer since it
	* was created, or since this method was last invoked, will have
	* been written to that device. The force operation is free to
	* write bytes that lie outside the specified region, for example
	* to ensure that data blocks of some device-specific granularity
	* are transferred in their entirety.
	*
	* <p> If the file does not reside on a local device then no such
	* guarantee is made.
	*
	* <p> If this buffer was not mapped in read/write mode ({@link
	* java.nio.channels.FileChannel.MapMode#READ_WRITE}) then
	* invoking this method may have no effect. In particular, the
	* method has no effect for buffers mapped in read-only or private
	* mapping modes. This method may or may not have an effect for
	* implementation-specific mapping modes. </p>
	*
	* @param index
	* The index of the first byte in the buffer region that is
	* to be written back to storage; must be non-negative
	* and less than {@code capacity()}
	*
	* @param length
	* The length of the region in bytes; must be non-negative
	* and no larger than {@code capacity() - index}
	*
	* @throws IndexOutOfBoundsException
	* if the preconditions on the index and length do not
	* hold.
	*
	* @throws UncheckedIOException
	* If an I/O error occurs writing the buffer's content to the
	* storage device containing the mapped file
	*
	* @return This buffer
	*
	* @since 13
	*/
	public final MappedByteBuffer force(int index, int length) {
	if (fd == null) {
	return this;
	}
	int capacity = capacity();
	if ((address != 0) && (capacity != 0)) {
	// check inputs
	Objects.checkFromIndexSize(index, length, capacity);
	SCOPED_MEMORY_ACCESS.force(scope(), fd, address, isSync, index, length);
	}
	return this;
	}

	// -- Covariant return type overrides

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer position(int newPosition) {
	super.position(newPosition);
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer limit(int newLimit) {
	super.limit(newLimit);
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer mark() {
	super.mark();
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer reset() {
	super.reset();
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer clear() {
	super.clear();
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer flip() {
	super.flip();
	return this;
	}

	/**
	* {@inheritDoc}
	*/
	@Override
	public final MappedByteBuffer rewind() {
	super.rewind();
	return this;
	}

	/**
	* {@inheritDoc}
	*
	* <p> Reading bytes into physical memory by invoking {@code load()} on the
	* returned buffer, or writing bytes to the storage device by invoking
	* {@code force()} on the returned buffer, will only act on the sub-range
	* of this buffer that the returned buffer represents, namely
	* {@code [position(),limit())}.
	*/
	@Override
	public abstract MappedByteBuffer slice();

	/**
	* {@inheritDoc}
	*
	* <p> Reading bytes into physical memory by invoking {@code load()} on the
	* returned buffer, or writing bytes to the storage device by invoking
	* {@code force()} on the returned buffer, will only act on the sub-range
	* of this buffer that the returned buffer represents, namely
	* {@code [index,index+length)}, where {@code index} and {@code length} are
	* assumed to satisfy the preconditions.
	*/
	@Override
	public abstract MappedByteBuffer slice(int index, int length);

	/**
	* {@inheritDoc}
	*/
	@Override
	public abstract MappedByteBuffer duplicate();

	/**
	* {@inheritDoc}
	*/
	@Override
	public abstract MappedByteBuffer compact();
	}

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