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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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).
 *
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 * 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.io;

import java.util.concurrent.atomic.AtomicInteger;

Instances of the file descriptor class serve as an opaque handle
to the underlying machine-specific structure representing an open
file, an open socket, or another source or sink of bytes. The
main practical use for a file descriptor is to create a
FileInputStream or FileOutputStream to
contain it.

Applications should not create their own file descriptors.
Author:
 Pavani Diwanji
See Also:
FileInputStream
FileOutputStream
Since:
  JDK1.0/**
 * Instances of the file descriptor class serve as an opaque handle
 * to the underlying machine-specific structure representing an open
 * file, an open socket, or another source or sink of bytes. The
 * main practical use for a file descriptor is to create a
 * <code>FileInputStream</code> or <code>FileOutputStream</code> to
 * contain it.
 * <p>
 * Applications should not create their own file descriptors.
 *
 * @author  Pavani Diwanji
 * @see     java.io.FileInputStream
 * @see     java.io.FileOutputStream
 * @since   JDK1.0
 */
public final class FileDescriptor {

    private int fd;

    
A counter for tracking the FIS/FOS/RAF instances that
use this FileDescriptor. The FIS/FOS.finalize() will not release
the FileDescriptor if it is still under user by a stream.
/**
     * A counter for tracking the FIS/FOS/RAF instances that
     * use this FileDescriptor. The FIS/FOS.finalize() will not release
     * the FileDescriptor if it is still under user by a stream.
     */
    private AtomicInteger useCount;

    
Constructs an (invalid) FileDescriptor
object.
/**
     * Constructs an (invalid) FileDescriptor
     * object.
     */
    public /**/ FileDescriptor() {
        fd = -1;
        useCount = new AtomicInteger();
    }

    private /* */ FileDescriptor(int fd) {
        this.fd = fd;
        useCount = new AtomicInteger();
    }

    
A handle to the standard input stream. Usually, this file
descriptor is not used directly, but rather via the input stream
known as System.in.
See Also:
in.in/**
     * A handle to the standard input stream. Usually, this file
     * descriptor is not used directly, but rather via the input stream
     * known as <code>System.in</code>.
     *
     * @see     java.lang.System#in
     */
    public static final FileDescriptor in = new FileDescriptor(0);

    
A handle to the standard output stream. Usually, this file
descriptor is not used directly, but rather via the output stream
known as System.out.
See Also:
out.out/**
     * A handle to the standard output stream. Usually, this file
     * descriptor is not used directly, but rather via the output stream
     * known as <code>System.out</code>.
     * @see     java.lang.System#out
     */
    public static final FileDescriptor out = new FileDescriptor(1);

    
A handle to the standard error stream. Usually, this file
descriptor is not used directly, but rather via the output stream
known as System.err.
See Also:
err.err/**
     * A handle to the standard error stream. Usually, this file
     * descriptor is not used directly, but rather via the output stream
     * known as <code>System.err</code>.
     *
     * @see     java.lang.System#err
     */
    public static final FileDescriptor err = new FileDescriptor(2);

    
Tests if this file descriptor object is valid.
Returns:
 true if the file descriptor object represents a
         valid, open file, socket, or other active I/O connection;
         false otherwise./**
     * Tests if this file descriptor object is valid.
     *
     * @return  <code>true</code> if the file descriptor object represents a
     *          valid, open file, socket, or other active I/O connection;
     *          <code>false</code> otherwise.
     */
    public boolean valid() {
        return fd != -1;
    }

    
Force all system buffers to synchronize with the underlying
device.  This method returns after all modified data and
attributes of this FileDescriptor have been written to the
relevant device(s).  In particular, if this FileDescriptor
refers to a physical storage medium, such as a file in a file
system, sync will not return until all in-memory modified copies
of buffers associated with this FileDescriptor have been
written to the physical medium.
sync is meant to be used by code that requires physical
storage (such as a file) to be in a known state  For
example, a class that provided a simple transaction facility
might use sync to ensure that all changes to a file caused
by a given transaction were recorded on a storage medium.
sync only affects buffers downstream of this FileDescriptor.  If
any in-memory buffering is being done by the application (for
example, by a BufferedOutputStream object), those buffers must
be flushed into the FileDescriptor (for example, by invoking
OutputStream.flush) before that data will be affected by sync.
Throws:
SyncFailedException – 
       Thrown when the buffers cannot be flushed,
       or because the system cannot guarantee that all the
       buffers have been synchronized with physical media.
Since:
    JDK1.1/**
     * Force all system buffers to synchronize with the underlying
     * device.  This method returns after all modified data and
     * attributes of this FileDescriptor have been written to the
     * relevant device(s).  In particular, if this FileDescriptor
     * refers to a physical storage medium, such as a file in a file
     * system, sync will not return until all in-memory modified copies
     * of buffers associated with this FileDescriptor have been
     * written to the physical medium.
     *
     * sync is meant to be used by code that requires physical
     * storage (such as a file) to be in a known state  For
     * example, a class that provided a simple transaction facility
     * might use sync to ensure that all changes to a file caused
     * by a given transaction were recorded on a storage medium.
     *
     * sync only affects buffers downstream of this FileDescriptor.  If
     * any in-memory buffering is being done by the application (for
     * example, by a BufferedOutputStream object), those buffers must
     * be flushed into the FileDescriptor (for example, by invoking
     * OutputStream.flush) before that data will be affected by sync.
     *
     * @exception SyncFailedException
     *        Thrown when the buffers cannot be flushed,
     *        or because the system cannot guarantee that all the
     *        buffers have been synchronized with physical media.
     * @since     JDK1.1
     */
    public native void sync() throws SyncFailedException;

    /* This routine initializes JNI field offsets for the class */
    private static native void initIDs();

    static {
        initIDs();
    }

    // Set up JavaIOFileDescriptorAccess in SharedSecrets
    static {
        sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
            new sun.misc.JavaIOFileDescriptorAccess() {
                public void set(FileDescriptor obj, int fd) {
                    obj.fd = fd;
                }

                public int get(FileDescriptor obj) {
                    return obj.fd;
                }
            }
        );
    }

    // pacakge private methods used by FIS,FOS and RAF

    int incrementAndGetUseCount() {
        return useCount.incrementAndGet();
    }

    int decrementAndGetUseCount() {
        return useCount.decrementAndGet();
    }
}