| /* |
| * Copyright (c) 2000, 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; |
| |
| import java.io.FileDescriptor; |
| 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 name="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; |
| |
| // This should only be invoked by the DirectByteBuffer constructors |
| // |
| MappedByteBuffer(int mark, int pos, int lim, int cap, // package-private |
| FileDescriptor fd) |
| { |
| super(mark, pos, lim, cap); |
| this.fd = fd; |
| } |
| |
| MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private |
| super(mark, pos, lim, cap); |
| this.fd = null; |
| } |
| |
| private void checkMapped() { |
| if (fd == null) |
| // Can only happen if a luser explicitly casts a direct byte buffer |
| throw new UnsupportedOperationException(); |
| } |
| |
| // Returns the distance (in bytes) of the buffer from the page aligned address |
| // of the mapping. Computed each time to avoid storing in every direct buffer. |
| private long mappingOffset() { |
| int ps = Bits.pageSize(); |
| long offset = address % ps; |
| return (offset >= 0) ? offset : (ps + offset); |
| } |
| |
| private long mappingAddress(long mappingOffset) { |
| return address - mappingOffset; |
| } |
| |
| private long mappingLength(long mappingOffset) { |
| return (long)capacity() + mappingOffset; |
| } |
| |
| /** |
| * 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() { |
| checkMapped(); |
| if ((address == 0) || (capacity() == 0)) |
| return true; |
| long offset = mappingOffset(); |
| long length = mappingLength(offset); |
| return isLoaded0(mappingAddress(offset), length, Bits.pageCount(length)); |
| } |
| |
| // not used, but a potential target for a store, see load() for details. |
| private static byte unused; |
| |
| /** |
| * 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() { |
| checkMapped(); |
| if ((address == 0) || (capacity() == 0)) |
| return this; |
| long offset = mappingOffset(); |
| long length = mappingLength(offset); |
| load0(mappingAddress(offset), length); |
| |
| // Read a byte from each page to bring it into memory. A checksum |
| // is computed as we go along to prevent the compiler from otherwise |
| // considering the loop as dead code. |
| Unsafe unsafe = Unsafe.getUnsafe(); |
| int ps = Bits.pageSize(); |
| int count = Bits.pageCount(length); |
| long a = mappingAddress(offset); |
| byte x = 0; |
| for (int i=0; i<count; i++) { |
| x ^= unsafe.getByte(a); |
| a += ps; |
| } |
| if (unused != 0) |
| unused = x; |
| |
| return this; |
| } |
| |
| /** |
| * Forces any changes made to this buffer's content to be written to the |
| * storage device containing the mapped file. |
| * |
| * <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 has no effect. </p> |
| * |
| * @return This buffer |
| */ |
| public final MappedByteBuffer force() { |
| checkMapped(); |
| if ((address != 0) && (capacity() != 0)) { |
| long offset = mappingOffset(); |
| force0(fd, mappingAddress(offset), mappingLength(offset)); |
| } |
| return this; |
| } |
| |
| private native boolean isLoaded0(long address, long length, int pageCount); |
| private native void load0(long address, long length); |
| private native void force0(FileDescriptor fd, long address, long length); |
| |
| // -- 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; |
| } |
| } |