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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* published by the Free Software Foundation. Oracle designates this
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*
* 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.
*
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*/
package java.nio;
/** {@collect.stats}
* 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
* @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, // package-private
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();
}
/** {@collect.stats}
* 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());
}
/** {@collect.stats}
* 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;
}
/** {@collect.stats}
* 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);
}