https://openjdk.java.net/ 
/*
 * Copyright (c) 2003, 2018, 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
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package java.io;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

import jdk.internal.misc.JavaIOFileDescriptorAccess;
import jdk.internal.misc.SharedSecrets;
import jdk.internal.ref.PhantomCleanable;


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
Since:  1.0
/**
 * 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
 * {@link FileInputStream} or {@link FileOutputStream} to contain it.
 * <p>
 * Applications should not create their own file descriptors.
 *
 * @author  Pavani Diwanji
 * @since   1.0
 */
public final class FileDescriptor {

    private int fd;

    private long handle;

    private Closeable parent;
    private List<Closeable> otherParents;
    private boolean closed;

    
true, if file is opened for appending.

/**
     * true, if file is opened for appending.
     */
    private boolean append;

    static {
        initIDs();
    }

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

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

                    public void setAppend(FileDescriptor fdo, boolean append) {
                        fdo.append = append;
                    }

                    public boolean getAppend(FileDescriptor fdo) {
                        return fdo.append;
                    }

                    public void close(FileDescriptor fdo) throws IOException {
                        fdo.close();
                    }

                    /* Register for a normal FileCleanable fd/handle cleanup. */
                    public void registerCleanup(FileDescriptor fdo) {
                        FileCleanable.register(fdo);
                    }

                    /* Register a custom PhantomCleanup. */
                    public void registerCleanup(FileDescriptor fdo,
                                                PhantomCleanable<FileDescriptor> cleanup) {
                        fdo.registerCleanup(cleanup);
                    }

                    public void unregisterCleanup(FileDescriptor fdo) {
                        fdo.unregisterCleanup();
                    }

                    public void setHandle(FileDescriptor fdo, long handle) {
                        fdo.setHandle(handle);
                    }

                    public long getHandle(FileDescriptor fdo) {
                        return fdo.handle;
                    }
                }
        );
    }

    
Cleanup in case FileDescriptor is not explicitly closed.

/**
     * Cleanup in case FileDescriptor is not explicitly closed.
     */
    private PhantomCleanable<FileDescriptor> cleanup;

    
Constructs an (invalid) FileDescriptor object.
The fd or handle is set later.

/**
     * Constructs an (invalid) FileDescriptor object.
     * The fd or handle is set later.
     */
    public FileDescriptor() {
        fd = -1;
        handle = -1;
    }

    
Used for standard input, output, and error only.
For Windows the corresponding handle is initialized.
For Unix the append mode is cached.

Params:
  • fd – the raw fd number (0, 1, 2)
/**
     * Used for standard input, output, and error only.
     * For Windows the corresponding handle is initialized.
     * For Unix the append mode is cached.
     * @param fd the raw fd number (0, 1, 2)
     */
    private FileDescriptor(int fd) {
        this.fd = fd;
        this.handle = getHandle(fd);
        this.append = getAppend(fd);
    }

    
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:
/**
     * 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}.
     *
     * @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:
/**
     * 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}.
     * @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:
/**
     * 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}.
     *
     * @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} if the file descriptor object represents a
     *          valid, open file, socket, or other active I/O connection;
     *          {@code false} otherwise.
     */
    public boolean valid() {
        return (handle != -1) || (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:    1.1
/**
     * 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     1.1
     */
    public native void sync() throws SyncFailedException;

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

    /*
     * On Windows return the handle for the standard streams.
     */
    private static native long getHandle(int d);

    
Returns true, if the file was opened for appending.

/**
     * Returns true, if the file was opened for appending.
     */
    private static native boolean getAppend(int fd);

    
Set the fd. Used on Unix and for sockets on Windows and Unix. If setting to -1, clear the cleaner. The registerCleanup method should be called for new fds. 
Params:
  • fd – the raw fd or -1 to indicate closed
/**
     * Set the fd.
     * Used on Unix and for sockets on Windows and Unix.
     * If setting to -1, clear the cleaner.
     * The {@link #registerCleanup} method should be called for new fds.
     * @param fd the raw fd or -1 to indicate closed
     */
    @SuppressWarnings("unchecked")
    synchronized void set(int fd) {
        if (fd == -1 && cleanup != null) {
            cleanup.clear();
            cleanup = null;
        }
        this.fd = fd;
    }

    
Set the handle. Used on Windows for regular files. If setting to -1, clear the cleaner. The registerCleanup method should be called for new handles. 
Params:
  • handle – the handle or -1 to indicate closed
/**
     * Set the handle.
     * Used on Windows for regular files.
     * If setting to -1, clear the cleaner.
     * The {@link #registerCleanup} method should be called for new handles.
     * @param handle the handle or -1 to indicate closed
     */
    @SuppressWarnings("unchecked")
    void setHandle(long handle) {
        if (handle == -1 && cleanup != null) {
            cleanup.clear();
            cleanup = null;
        }
        this.handle = handle;
    }

    
Register a cleanup for the current handle.
Used directly in java.io and indirectly via fdAccess.
The cleanup should be registered after the handle is set in the FileDescriptor.

Params:
  • cleanable – a PhantomCleanable to register
/**
     * Register a cleanup for the current handle.
     * Used directly in java.io and indirectly via fdAccess.
     * The cleanup should be registered after the handle is set in the FileDescriptor.
     * @param cleanable a PhantomCleanable to register
     */
    @SuppressWarnings("unchecked")
    synchronized void registerCleanup(PhantomCleanable<FileDescriptor> cleanable) {
        Objects.requireNonNull(cleanable, "cleanable");
        if (cleanup != null) {
            cleanup.clear();
        }
        cleanup = cleanable;
    }

    
Unregister a cleanup for the current raw fd or handle. Used directly in java.io and indirectly via fdAccess. Normally close() should be used except in cases where it is certain the caller will close the raw fd and the cleanup must not close the raw fd. unregisterCleanup() must be called before the raw fd is closed to prevent a race that makes it possible for the fd to be reallocated to another use and later the cleanup might be invoked. 
/**
     * Unregister a cleanup for the current raw fd or handle.
     * Used directly in java.io and indirectly via fdAccess.
     * Normally {@link #close()} should be used except in cases where
     * it is certain the caller will close the raw fd and the cleanup
     * must not close the raw fd.  {@link #unregisterCleanup()} must be
     * called before the raw fd is closed to prevent a race that makes
     * it possible for the fd to be reallocated to another use and later
     * the cleanup might be invoked.
     */
    synchronized void unregisterCleanup() {
        if (cleanup != null) {
            cleanup.clear();
        }
        cleanup = null;
    }

    
Close the raw file descriptor or handle, if it has not already been closed.
The native code sets the fd and handle to -1.
Clear the cleaner so the close does not happen twice.
Package private to allow it to be used in java.io.

Throws:
  • IOException – if close fails
/**
     * Close the raw file descriptor or handle, if it has not already been closed.
     * The native code sets the fd and handle to -1.
     * Clear the cleaner so the close does not happen twice.
     * Package private to allow it to be used in java.io.
     * @throws IOException if close fails
     */
    @SuppressWarnings("unchecked")
    synchronized void close() throws IOException {
        unregisterCleanup();
        close0();
    }

    /*
     * Close the raw file descriptor or handle, if it has not already been closed
     * and set the fd and handle to -1.
     */
    private native void close0() throws IOException;

    /*
     * Package private methods to track referents.
     * If multiple streams point to the same FileDescriptor, we cycle
     * through the list of all referents and call close()
     */

    
Attach a Closeable to this FD for tracking.
parent reference is added to otherParents when
needed to make closeAll simpler.

/**
     * Attach a Closeable to this FD for tracking.
     * parent reference is added to otherParents when
     * needed to make closeAll simpler.
     */
    synchronized void attach(Closeable c) {
        if (parent == null) {
            // first caller gets to do this
            parent = c;
        } else if (otherParents == null) {
            otherParents = new ArrayList<>();
            otherParents.add(parent);
            otherParents.add(c);
        } else {
            otherParents.add(c);
        }
    }

    
Cycle through all Closeables sharing this FD and call
close() on each one.
The caller closeable gets to call close0().

/**
     * Cycle through all Closeables sharing this FD and call
     * close() on each one.
     *
     * The caller closeable gets to call close0().
     */
    @SuppressWarnings("try")
    synchronized void closeAll(Closeable releaser) throws IOException {
        if (!closed) {
            closed = true;
            IOException ioe = null;
            try (releaser) {
                if (otherParents != null) {
                    for (Closeable referent : otherParents) {
                        try {
                            referent.close();
                        } catch(IOException x) {
                            if (ioe == null) {
                                ioe = x;
                            } else {
                                ioe.addSuppressed(x);
                            }
                        }
                    }
                }
            } catch(IOException ex) {
                /*
                 * If releaser close() throws IOException
                 * add other exceptions as suppressed.
                 */
                if (ioe != null)
                    ex.addSuppressed(ioe);
                ioe = ex;
            } finally {
                if (ioe != null)
                    throw ioe;
            }
        }
    }
}