1 /*
2 * Copyright (c) 1995, 2008, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.io;
27
28 import java.util.concurrent.atomic.AtomicInteger;
29
30 /**
31 * Instances of the file descriptor class serve as an opaque handle
32 * to the underlying machine-specific structure representing an open
33 * file, an open socket, or another source or sink of bytes. The
34 * main practical use for a file descriptor is to create a
35 * <code>FileInputStream</code> or <code>FileOutputStream</code> to
36 * contain it.
37 * <p>
38 * Applications should not create their own file descriptors.
39 *
40 * @author Pavani Diwanji
41 * @see java.io.FileInputStream
42 * @see java.io.FileOutputStream
43 * @since JDK1.0
44 */
45 public final class FileDescriptor {
46
47 private int fd;
48
49 /**
50 * A counter for tracking the FIS/FOS/RAF instances that
51 * use this FileDescriptor. The FIS/FOS.finalize() will not release
52 * the FileDescriptor if it is still under user by a stream.
53 */
54 private AtomicInteger useCount;
55
56 /**
57 * Constructs an (invalid) FileDescriptor
58 * object.
59 */
60 public /**/ FileDescriptor() {
61 fd = -1;
62 useCount = new AtomicInteger();
63 }
64
65 private /* */ FileDescriptor(int fd) {
66 this.fd = fd;
67 useCount = new AtomicInteger();
68 }
69
70 /**
71 * A handle to the standard input stream. Usually, this file
72 * descriptor is not used directly, but rather via the input stream
73 * known as <code>System.in</code>.
74 *
75 * @see java.lang.System#in
76 */
77 public static final FileDescriptor in = new FileDescriptor(0);
78
79 /**
80 * A handle to the standard output stream. Usually, this file
81 * descriptor is not used directly, but rather via the output stream
82 * known as <code>System.out</code>.
83 * @see java.lang.System#out
84 */
85 public static final FileDescriptor out = new FileDescriptor(1);
86
87 /**
88 * A handle to the standard error stream. Usually, this file
89 * descriptor is not used directly, but rather via the output stream
90 * known as <code>System.err</code>.
91 *
92 * @see java.lang.System#err
93 */
94 public static final FileDescriptor err = new FileDescriptor(2);
95
96 /**
97 * Tests if this file descriptor object is valid.
98 *
99 * @return <code>true</code> if the file descriptor object represents a
100 * valid, open file, socket, or other active I/O connection;
101 * <code>false</code> otherwise.
102 */
103 public boolean valid() {
104 return fd != -1;
105 }
106
107 /**
108 * Force all system buffers to synchronize with the underlying
109 * device. This method returns after all modified data and
110 * attributes of this FileDescriptor have been written to the
111 * relevant device(s). In particular, if this FileDescriptor
112 * refers to a physical storage medium, such as a file in a file
113 * system, sync will not return until all in-memory modified copies
114 * of buffers associated with this FileDescriptor have been
115 * written to the physical medium.
116 *
117 * sync is meant to be used by code that requires physical
118 * storage (such as a file) to be in a known state For
119 * example, a class that provided a simple transaction facility
120 * might use sync to ensure that all changes to a file caused
121 * by a given transaction were recorded on a storage medium.
122 *
123 * sync only affects buffers downstream of this FileDescriptor. If
124 * any in-memory buffering is being done by the application (for
125 * example, by a BufferedOutputStream object), those buffers must
126 * be flushed into the FileDescriptor (for example, by invoking
127 * OutputStream.flush) before that data will be affected by sync.
128 *
129 * @exception SyncFailedException
130 * Thrown when the buffers cannot be flushed,
131 * or because the system cannot guarantee that all the
132 * buffers have been synchronized with physical media.
133 * @since JDK1.1
134 */
135 public native void sync() throws SyncFailedException;
136
137 /* This routine initializes JNI field offsets for the class */
138 private static native void initIDs();
139
140 static {
141 initIDs();
142 }
143
144 // Set up JavaIOFileDescriptorAccess in SharedSecrets
145 static {
146 sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
147 new sun.misc.JavaIOFileDescriptorAccess() {
148 public void set(FileDescriptor obj, int fd) {
149 obj.fd = fd;
150 }
151
152 public int get(FileDescriptor obj) {
153 return obj.fd;
154 }
155
156 public void setHandle(FileDescriptor obj, long handle) {
157 throw new UnsupportedOperationException();
158 }
159
160 public long getHandle(FileDescriptor obj) {
161 throw new UnsupportedOperationException();
162 }
163 }
164 );
165 }
166
167 // package private methods used by FIS, FOS and RAF
168
169 int incrementAndGetUseCount() {
170 return useCount.incrementAndGet();
171 }
172
173 int decrementAndGetUseCount() {
174 return useCount.decrementAndGet();
175 }
176 }