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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
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package java.nio;
import jdk.internal.access.JavaNioAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.access.foreign.MemorySegmentProxy;
import jdk.internal.access.foreign.UnmapperProxy;
import jdk.internal.misc.ScopedMemoryAccess;
import jdk.internal.misc.ScopedMemoryAccess.Scope;
import jdk.internal.misc.Unsafe;
import jdk.internal.misc.VM.BufferPool;
import jdk.internal.vm.annotation.ForceInline;
import jdk.internal.vm.annotation.IntrinsicCandidate;
import java.io.FileDescriptor;
import java.util.Spliterator;
/**
* A container for data of a specific primitive type.
*
* A buffer is a linear, finite sequence of elements of a specific
* primitive type. Aside from its content, the essential properties of a
* buffer are its capacity, limit, and position:
*
*
*
* A buffer's capacity is the number of elements it contains. The
* capacity of a buffer is never negative and never changes.
*
* A buffer's limit is the index of the first element that should
* not be read or written. A buffer's limit is never negative and is never
* greater than its capacity.
*
* A buffer's position is the index of the next element to be
* read or written. A buffer's position is never negative and is never
* greater than its limit.
*
*
*
* There is one subclass of this class for each non-boolean primitive type.
*
*
*
Transferring data
*
* Each subclass of this class defines two categories of get and
* put operations:
*
*
*
* Relative operations read or write one or more elements starting
* at the current position and then increment the position by the number of
* elements transferred. If the requested transfer exceeds the limit then a
* relative get operation throws a {@link BufferUnderflowException}
* and a relative put operation throws a {@link
* BufferOverflowException}; in either case, no data is transferred.
*
* Absolute operations take an explicit element index and do not
* affect the position. Absolute get and put operations throw
* an {@link IndexOutOfBoundsException} if the index argument exceeds the
* limit.
*
*
*
* Data may also, of course, be transferred in to or out of a buffer by the
* I/O operations of an appropriate channel, which are always relative to the
* current position.
*
*
*
Marking and resetting
*
* A buffer's mark is the index to which its position will be reset
* when the {@link #reset reset} method is invoked. The mark is not always
* defined, but when it is defined it is never negative and is never greater
* than the position. If the mark is defined then it is discarded when the
* position or the limit is adjusted to a value smaller than the mark. If the
* mark is not defined then invoking the {@link #reset reset} method causes an
* {@link InvalidMarkException} to be thrown.
*
*
*
Invariants
*
* The following invariant holds for the mark, position, limit, and
* capacity values:
*
*
* {@code 0} {@code <=}
* mark {@code <=}
* position {@code <=}
* limit {@code <=}
* capacity
*
*
* A newly-created buffer always has a position of zero and a mark that is
* undefined. The initial limit may be zero, or it may be some other value
* that depends upon the type of the buffer and the manner in which it is
* constructed. Each element of a newly-allocated buffer is initialized
* to zero.
*
*
*
Additional operations
*
* In addition to methods for accessing the position, limit, and capacity
* values and for marking and resetting, this class also defines the following
* operations upon buffers:
*
*
*
* {@link #clear} makes a buffer ready for a new sequence of
* channel-read or relative put operations: It sets the limit to the
* capacity and the position to zero.
{@link #flip} makes a buffer ready for a new sequence of
* channel-write or relative get operations: It sets the limit to the
* current position and then sets the position to zero.
{@link #rewind} makes a buffer ready for re-reading the data that
* it already contains: It leaves the limit unchanged and sets the position
* to zero.
The {@link #slice} and {@link #slice(int,int) slice(index,length)}
* methods create a subsequence of a buffer: They leave the limit and the
* position unchanged.
{@link #duplicate} creates a shallow copy of a buffer: It leaves
* the limit and the position unchanged.
*
*
* Read-only buffers
*
* Every buffer is readable, but not every buffer is writable. The
* mutation methods of each buffer class are specified as optional
* operations that will throw a {@link ReadOnlyBufferException} when
* invoked upon a read-only buffer. A read-only buffer does not allow its
* content to be changed, but its mark, position, and limit values are mutable.
* Whether or not a buffer is read-only may be determined by invoking its
* {@link #isReadOnly isReadOnly} method.
*
*
*
Thread safety
*
* Buffers are not safe for use by multiple concurrent threads. If a
* buffer is to be used by more than one thread then access to the buffer
* should be controlled by appropriate synchronization.
*
*
*
Invocation chaining
*
* Methods in this class that do not otherwise have a value to return are
* specified to return the buffer upon which they are invoked. This allows
* method invocations to be chained; for example, the sequence of statements
*
*
* b.flip();
* b.position(23);
* b.limit(42);
*
* can be replaced by the single, more compact statement
*
*
* b.flip().position(23).limit(42);
*
*
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class Buffer {
// Cached unsafe-access object
static final Unsafe UNSAFE = Unsafe.getUnsafe();
static final ScopedMemoryAccess SCOPED_MEMORY_ACCESS = ScopedMemoryAccess.getScopedMemoryAccess();
/**
* The characteristics of Spliterators that traverse and split elements
* maintained in Buffers.
*/
static final int SPLITERATOR_CHARACTERISTICS =
Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.ORDERED;
// Invariants: mark <= position <= limit <= capacity
private int mark = -1;
private int position = 0;
private int limit;
private int capacity;
// Used by heap byte buffers or direct buffers with Unsafe access
// For heap byte buffers this field will be the address relative to the
// array base address and offset into that array. The address might
// not align on a word boundary for slices, nor align at a long word
// (8 byte) boundary for byte[] allocations on 32-bit systems.
// For direct buffers it is the start address of the memory region. The
// address might not align on a word boundary for slices, nor when created
// using JNI, see NewDirectByteBuffer(void*, long).
// Should ideally be declared final
// NOTE: hoisted here for speed in JNI GetDirectBufferAddress
long address;
// Used by buffers generated by the memory access API (JEP-370)
final MemorySegmentProxy segment;
// Creates a new buffer with given address and capacity.
//
Buffer(long addr, int cap, MemorySegmentProxy segment) {
this.address = addr;
this.capacity = cap;
this.segment = segment;
}
// Creates a new buffer with the given mark, position, limit, and capacity,
// after checking invariants.
//
Buffer(int mark, int pos, int lim, int cap, MemorySegmentProxy segment) { // package-private
if (cap < 0)
throw createCapacityException(cap);
this.capacity = cap;
this.segment = segment;
limit(lim);
position(pos);
if (mark >= 0) {
if (mark > pos)
throw new IllegalArgumentException("mark > position: ("
+ mark + " > " + pos + ")");
this.mark = mark;
}
}
/**
* Returns an {@code IllegalArgumentException} indicating that the source
* and target are the same {@code Buffer}. Intended for use in
* {@code put(src)} when the parameter is the {@code Buffer} on which the
* method is being invoked.
*
* @return IllegalArgumentException
* With a message indicating equal source and target buffers
*/
static IllegalArgumentException createSameBufferException() {
return new IllegalArgumentException("The source buffer is this buffer");
}
/**
* Verify that the capacity is nonnegative.
*
* @param capacity
* The new buffer's capacity, in $type$s
*
* @throws IllegalArgumentException
* If the {@code capacity} is a negative integer
*/
static IllegalArgumentException createCapacityException(int capacity) {
assert capacity < 0 : "capacity expected to be negative";
return new IllegalArgumentException("capacity < 0: ("
+ capacity + " < 0)");
}
/**
* Returns this buffer's capacity.
*
* @return The capacity of this buffer
*/
public final int capacity() {
return capacity;
}
/**
* Returns this buffer's position.
*
* @return The position of this buffer
*/
public final int position() {
return position;
}
/**
* Sets this buffer's position. If the mark is defined and larger than the
* new position then it is discarded.
*
* @param newPosition
* The new position value; must be non-negative
* and no larger than the current limit
*
* @return This buffer
*
* @throws IllegalArgumentException
* If the preconditions on {@code newPosition} do not hold
*/
public Buffer position(int newPosition) {
if (newPosition > limit | newPosition < 0)
throw createPositionException(newPosition);
if (mark > newPosition) mark = -1;
position = newPosition;
return this;
}
/**
* Verify that {@code 0 < newPosition <= limit}
*
* @param newPosition
* The new position value
*
* @throws IllegalArgumentException
* If the specified position is out of bounds.
*/
private IllegalArgumentException createPositionException(int newPosition) {
String msg = null;
if (newPosition > limit) {
msg = "newPosition > limit: (" + newPosition + " > " + limit + ")";
} else { // assume negative
assert newPosition < 0 : "newPosition expected to be negative";
msg = "newPosition < 0: (" + newPosition + " < 0)";
}
return new IllegalArgumentException(msg);
}
/**
* Returns this buffer's limit.
*
* @return The limit of this buffer
*/
public final int limit() {
return limit;
}
/**
* Sets this buffer's limit. If the position is larger than the new limit
* then it is set to the new limit. If the mark is defined and larger than
* the new limit then it is discarded.
*
* @param newLimit
* The new limit value; must be non-negative
* and no larger than this buffer's capacity
*
* @return This buffer
*
* @throws IllegalArgumentException
* If the preconditions on {@code newLimit} do not hold
*/
public Buffer limit(int newLimit) {
if (newLimit > capacity | newLimit < 0)
throw createLimitException(newLimit);
limit = newLimit;
if (position > newLimit) position = newLimit;
if (mark > newLimit) mark = -1;
return this;
}
/**
* Verify that {@code 0 < newLimit <= capacity}
*
* @param newLimit
* The new limit value
*
* @throws IllegalArgumentException
* If the specified limit is out of bounds.
*/
private IllegalArgumentException createLimitException(int newLimit) {
String msg = null;
if (newLimit > capacity) {
msg = "newLimit > capacity: (" + newLimit + " > " + capacity + ")";
} else { // assume negative
assert newLimit < 0 : "newLimit expected to be negative";
msg = "newLimit < 0: (" + newLimit + " < 0)";
}
return new IllegalArgumentException(msg);
}
/**
* Sets this buffer's mark at its position.
*
* @return This buffer
*/
public Buffer mark() {
mark = position;
return this;
}
/**
* Resets this buffer's position to the previously-marked position.
*
* Invoking this method neither changes nor discards the mark's
* value.
*
* @return This buffer
*
* @throws InvalidMarkException
* If the mark has not been set
*/
public Buffer reset() {
int m = mark;
if (m < 0)
throw new InvalidMarkException();
position = m;
return this;
}
/**
* Clears this buffer. The position is set to zero, the limit is set to
* the capacity, and the mark is discarded.
*
* Invoke this method before using a sequence of channel-read or
* put operations to fill this buffer. For example:
*
*
* buf.clear(); // Prepare buffer for reading
* in.read(buf); // Read data
*
* This method does not actually erase the data in the buffer, but it
* is named as if it did because it will most often be used in situations
* in which that might as well be the case.
*
* @return This buffer
*/
public Buffer clear() {
position = 0;
limit = capacity;
mark = -1;
return this;
}
/**
* Flips this buffer. The limit is set to the current position and then
* the position is set to zero. If the mark is defined then it is
* discarded.
*
* After a sequence of channel-read or put operations, invoke
* this method to prepare for a sequence of channel-write or relative
* get operations. For example:
*
*
* buf.put(magic); // Prepend header
* in.read(buf); // Read data into rest of buffer
* buf.flip(); // Flip buffer
* out.write(buf); // Write header + data to channel
*
* This method is often used in conjunction with the {@link
* java.nio.ByteBuffer#compact compact} method when transferring data from
* one place to another.
*
* @return This buffer
*/
public Buffer flip() {
limit = position;
position = 0;
mark = -1;
return this;
}
/**
* Rewinds this buffer. The position is set to zero and the mark is
* discarded.
*
* Invoke this method before a sequence of channel-write or get
* operations, assuming that the limit has already been set
* appropriately. For example:
*
*
* out.write(buf); // Write remaining data
* buf.rewind(); // Rewind buffer
* buf.get(array); // Copy data into array
*
* @return This buffer
*/
public Buffer rewind() {
position = 0;
mark = -1;
return this;
}
/**
* Returns the number of elements between the current position and the
* limit.
*
* @return The number of elements remaining in this buffer
*/
public final int remaining() {
int rem = limit - position;
return rem > 0 ? rem : 0;
}
/**
* Tells whether there are any elements between the current position and
* the limit.
*
* @return {@code true} if, and only if, there is at least one element
* remaining in this buffer
*/
public final boolean hasRemaining() {
return position < limit;
}
/**
* Tells whether or not this buffer is read-only.
*
* @return {@code true} if, and only if, this buffer is read-only
*/
public abstract boolean isReadOnly();
/**
* Tells whether or not this buffer is backed by an accessible
* array.
*
* If this method returns {@code true} then the {@link #array() array}
* and {@link #arrayOffset() arrayOffset} methods may safely be invoked.
*
*
* @return {@code true} if, and only if, this buffer
* is backed by an array and is not read-only
*
* @since 1.6
*/
public abstract boolean hasArray();
/**
* Returns the array that backs this
* buffer (optional operation).
*
* This method is intended to allow array-backed buffers to be
* passed to native code more efficiently. Concrete subclasses
* provide more strongly-typed return values for this method.
*
*
Modifications to this buffer's content will cause the returned
* array's content to be modified, and vice versa.
*
*
Invoke the {@link #hasArray hasArray} method before invoking this
* method in order to ensure that this buffer has an accessible backing
* array.
*
* @return The array that backs this buffer
*
* @throws ReadOnlyBufferException
* If this buffer is backed by an array but is read-only
*
* @throws UnsupportedOperationException
* If this buffer is not backed by an accessible array
*
* @since 1.6
*/
public abstract Object array();
/**
* Returns the offset within this buffer's backing array of the first
* element of the buffer (optional operation).
*
* If this buffer is backed by an array then buffer position p
* corresponds to array index p + {@code arrayOffset()}.
*
*
Invoke the {@link #hasArray hasArray} method before invoking this
* method in order to ensure that this buffer has an accessible backing
* array.
*
* @return The offset within this buffer's array
* of the first element of the buffer
*
* @throws ReadOnlyBufferException
* If this buffer is backed by an array but is read-only
*
* @throws UnsupportedOperationException
* If this buffer is not backed by an accessible array
*
* @since 1.6
*/
public abstract int arrayOffset();
/**
* Tells whether or not this buffer is
* direct.
*
* @return {@code true} if, and only if, this buffer is direct
*
* @since 1.6
*/
public abstract boolean isDirect();
/**
* Creates a new buffer whose content is a shared subsequence of
* this buffer's content.
*
* The content of the new buffer will start at this buffer's current
* position. Changes to this buffer's content will be visible in the new
* buffer, and vice versa; the two buffers' position, limit, and mark
* values will be independent.
*
*
The new buffer's position will be zero, its capacity and its limit
* will be the number of elements remaining in this buffer, its mark will be
* undefined. The new buffer will be direct if, and only if, this buffer is
* direct, and it will be read-only if, and only if, this buffer is
* read-only.
*
* @return The new buffer
*
* @since 9
*/
public abstract Buffer slice();
/**
* Creates a new buffer whose content is a shared subsequence of
* this buffer's content.
*
* The content of the new buffer will start at position {@code index}
* in this buffer, and will contain {@code length} elements. Changes to
* this buffer's content will be visible in the new buffer, and vice versa;
* the two buffers' position, limit, and mark values will be independent.
*
*
The new buffer's position will be zero, its capacity and its limit
* will be {@code length}, its mark will be undefined. The new buffer will
* be direct if, and only if, this buffer is direct, and it will be
* read-only if, and only if, this buffer is read-only.
*
* @param index
* The position in this buffer at which the content of the new
* buffer will start; must be non-negative and no larger than
* {@link #limit() limit()}
*
* @param length
* The number of elements the new buffer will contain; must be
* non-negative and no larger than {@code limit() - index}
*
* @return The new buffer
*
* @throws IndexOutOfBoundsException
* If {@code index} is negative or greater than {@code limit()},
* {@code length} is negative, or {@code length > limit() - index}
*
* @since 13
*/
public abstract Buffer slice(int index, int length);
/**
* Creates a new buffer that shares this buffer's content.
*
* The content of the new buffer will be that of this buffer. Changes
* to this buffer's content will be visible in the new buffer, and vice
* versa; the two buffers' position, limit, and mark values will be
* independent.
*
*
The new buffer's capacity, limit, position and mark values will be
* identical to those of this buffer. The new buffer will be direct if, and
* only if, this buffer is direct, and it will be read-only if, and only if,
* this buffer is read-only.
*
* @return The new buffer
*
* @since 9
*/
public abstract Buffer duplicate();
// -- Package-private methods for bounds checking, etc. --
/**
*
* @return the base reference, paired with the address
* field, which in combination can be used for unsafe access into a heap
* buffer or direct byte buffer (and views of).
*/
abstract Object base();
/**
* Checks the current position against the limit, throwing a {@link
* BufferUnderflowException} if it is not smaller than the limit, and then
* increments the position.
*
* @return The current position value, before it is incremented
*/
final int nextGetIndex() { // package-private
int p = position;
if (p >= limit)
throw new BufferUnderflowException();
position = p + 1;
return p;
}
final int nextGetIndex(int nb) { // package-private
int p = position;
if (limit - p < nb)
throw new BufferUnderflowException();
position = p + nb;
return p;
}
/**
* Checks the current position against the limit, throwing a {@link
* BufferOverflowException} if it is not smaller than the limit, and then
* increments the position.
*
* @return The current position value, before it is incremented
*/
final int nextPutIndex() { // package-private
int p = position;
if (p >= limit)
throw new BufferOverflowException();
position = p + 1;
return p;
}
final int nextPutIndex(int nb) { // package-private
int p = position;
if (limit - p < nb)
throw new BufferOverflowException();
position = p + nb;
return p;
}
/**
* Checks the given index against the limit, throwing an {@link
* IndexOutOfBoundsException} if it is not smaller than the limit
* or is smaller than zero.
*/
@IntrinsicCandidate
final int checkIndex(int i) { // package-private
if ((i < 0) || (i >= limit))
throw new IndexOutOfBoundsException();
return i;
}
final int checkIndex(int i, int nb) { // package-private
if ((i < 0) || (nb > limit - i))
throw new IndexOutOfBoundsException();
return i;
}
final int markValue() { // package-private
return mark;
}
final void discardMark() { // package-private
mark = -1;
}
@ForceInline
final ScopedMemoryAccess.Scope scope() {
if (segment != null) {
return segment.scope();
} else {
return null;
}
}
final void checkScope() {
ScopedMemoryAccess.Scope scope = scope();
if (scope != null) {
scope.checkValidState();
}
}
static {
// setup access to this package in SharedSecrets
SharedSecrets.setJavaNioAccess(
new JavaNioAccess() {
@Override
public BufferPool getDirectBufferPool() {
return Bits.BUFFER_POOL;
}
@Override
public ByteBuffer newDirectByteBuffer(long addr, int cap, Object obj, MemorySegmentProxy segment) {
return new DirectByteBuffer(addr, cap, obj, segment);
}
@Override
public ByteBuffer newMappedByteBuffer(UnmapperProxy unmapperProxy, long address, int cap, Object obj, MemorySegmentProxy segment) {
return new DirectByteBuffer(address, cap, obj, unmapperProxy.fileDescriptor(), unmapperProxy.isSync(), segment);
}
@Override
public ByteBuffer newHeapByteBuffer(byte[] hb, int offset, int capacity, MemorySegmentProxy segment) {
return new HeapByteBuffer(hb, -1, 0, capacity, capacity, offset, segment);
}
@Override
public Object getBufferBase(ByteBuffer bb) {
return bb.base();
}
@Override
public long getBufferAddress(ByteBuffer bb) {
return bb.address;
}
@Override
public UnmapperProxy unmapper(ByteBuffer bb) {
if (bb instanceof MappedByteBuffer) {
return ((MappedByteBuffer)bb).unmapper();
} else {
return null;
}
}
@Override
public MemorySegmentProxy bufferSegment(Buffer buffer) {
return buffer.segment;
}
@Override
public Scope.Handle acquireScope(Buffer buffer, boolean async) {
var scope = buffer.scope();
if (scope == null) {
return null;
}
if (async && scope.ownerThread() != null) {
throw new IllegalStateException("Confined scope not supported");
}
return scope.acquire();
}
@Override
public void force(FileDescriptor fd, long address, boolean isSync, long offset, long size) {
MappedMemoryUtils.force(fd, address, isSync, offset, size);
}
@Override
public void load(long address, boolean isSync, long size) {
MappedMemoryUtils.load(address, isSync, size);
}
@Override
public void unload(long address, boolean isSync, long size) {
MappedMemoryUtils.unload(address, isSync, size);
}
@Override
public boolean isLoaded(long address, boolean isSync, long size) {
return MappedMemoryUtils.isLoaded(address, isSync, size);
}
@Override
public void reserveMemory(long size, long cap) {
Bits.reserveMemory(size, cap);
}
@Override
public void unreserveMemory(long size, long cap) {
Bits.unreserveMemory(size, cap);
}
@Override
public int pageSize() {
return Bits.pageSize();
}
});
}
}