/*

 * Copyright (c) 1995, 2012, Oracle and/or its affiliates. All rights reserved.

 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 *

 */

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

 * <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.

     */

    private AtomicInteger useCount;

    /**

     * 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 <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 <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 <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.

     *

     * @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.

     *

     * @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;

                }

                public void setHandle(FileDescriptor obj, long handle) {

                    throw new UnsupportedOperationException();

                }

                public long getHandle(FileDescriptor obj) {

                    throw new UnsupportedOperationException();

                }

            }

        );

    }

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

    int incrementAndGetUseCount() {

        return useCount.incrementAndGet();

    }

    int decrementAndGetUseCount() {

        return useCount.decrementAndGet();

    }

}