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/* * @(#)MappedByteBuffer.java 1.24 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.nio; /** * 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"><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 * @version 1.24, 05/11/17 * @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. // Volatile to make sure that the finalization thread sees the current // value of this so that a region is not accidentally unmapped again later. volatile boolean isAMappedBuffer; // package-private // This should only be invoked by the DirectByteBuffer constructors // MappedByteBuffer(int mark, int pos, int lim, int cap, __JOT_PIECE_14__ boolean mapped) { super(mark, pos, lim, cap); isAMappedBuffer = mapped; } MappedByteBuffer(int mark, int pos, int lim, int cap) { // package-private super(mark, pos, lim, cap); isAMappedBuffer = false; } private void checkMapped() { if (!isAMappedBuffer) // Can only happen if a luser explicitly casts a direct byte buffer throw new UnsupportedOperationException(); } /** * Tells whether or not this buffer's content is resident in physical * memory. * * <p> A return value of <tt>true</tt> 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 <tt>false</tt> 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 <tt>true</tt> 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; return isLoaded0(((DirectByteBuffer)this).address(), 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() { checkMapped(); if ((address == 0) || (capacity() == 0)) return this; load0(((DirectByteBuffer)this).address(), capacity(), Bits.pageSize()); 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)) return this; force0(((DirectByteBuffer)this).address(), capacity()); return this; } private native boolean isLoaded0(long address, long length); private native int load0(long address, long length, int pageSize); private native void force0(long address, long length); }