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/*
* Copyright (c) 2003, 2025, 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
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.io;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import jdk.internal.access.JavaIOFileDescriptorAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.misc.Blocker;
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
* {@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.
*/
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.
*/
private PhantomCleanable<FileDescriptor> cleanup;
/**
* 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.
* @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 {@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 {@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 {@code System.err}.
*
* @see java.lang.System#err
*/
public static final FileDescriptor err = new FileDescriptor(2);
/**
* 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
*/
public void sync() throws SyncFailedException {
boolean attempted = Blocker.begin();
try {
sync0();
} finally {
Blocker.end(attempted);
}
}
/* fsync/equivalent this file descriptor */
private native void sync0() 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.
*/
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 {@link #registerCleanup} method should be called for new fds.
* @param fd the raw fd or -1 to indicate closed
*/
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 {@link #registerCleanup} method should be called for new handles.
* @param handle the handle or -1 to indicate closed
*/
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.
* @param cleanable a PhantomCleanable to register
*/
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 {@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
*/
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.
*/
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().
*/
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;
}
}
}
}