1 /*
2 * Copyright (c) 1995, 2011, 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.ArrayList;
29 import java.util.List;
30
31 /**
32 * Instances of the file descriptor class serve as an opaque handle
33 * to the underlying machine-specific structure representing an open
34 * file, an open socket, or another source or sink of bytes. The
35 * main practical use for a file descriptor is to create a
36 * <code>FileInputStream</code> or <code>FileOutputStream</code> to
37 * contain it.
38 * <p>
39 * Applications should not create their own file descriptors.
40 *
41 * @author Pavani Diwanji
42 * @see java.io.FileInputStream
43 * @see java.io.FileOutputStream
44 * @since 1.0
45 */
46 public final class FileDescriptor {
47
48 private int fd;
49
50 private Closeable parent;
51 private List<Closeable> otherParents;
52 private boolean closed;
53
54 /**
55 * Constructs an (invalid) FileDescriptor
56 * object.
57 */
58 public /**/ FileDescriptor() {
59 fd = -1;
60 }
61
62 private /* */ FileDescriptor(int fd) {
63 this.fd = fd;
64 }
65
66 /**
67 * A handle to the standard input stream. Usually, this file
68 * descriptor is not used directly, but rather via the input stream
69 * known as <code>System.in</code>.
70 *
71 * @see java.lang.System#in
72 */
73 public static final FileDescriptor in = new FileDescriptor(0);
74
75 /**
76 * A handle to the standard output stream. Usually, this file
77 * descriptor is not used directly, but rather via the output stream
78 * known as <code>System.out</code>.
79 * @see java.lang.System#out
80 */
81 public static final FileDescriptor out = new FileDescriptor(1);
82
83 /**
84 * A handle to the standard error stream. Usually, this file
85 * descriptor is not used directly, but rather via the output stream
86 * known as <code>System.err</code>.
87 *
88 * @see java.lang.System#err
89 */
90 public static final FileDescriptor err = new FileDescriptor(2);
91
92 /**
93 * Tests if this file descriptor object is valid.
94 *
95 * @return <code>true</code> if the file descriptor object represents a
96 * valid, open file, socket, or other active I/O connection;
97 * <code>false</code> otherwise.
98 */
99 public boolean valid() {
100 return fd != -1;
101 }
102
103 /**
104 * Force all system buffers to synchronize with the underlying
105 * device. This method returns after all modified data and
106 * attributes of this FileDescriptor have been written to the
107 * relevant device(s). In particular, if this FileDescriptor
108 * refers to a physical storage medium, such as a file in a file
109 * system, sync will not return until all in-memory modified copies
110 * of buffers associated with this FileDescriptor have been
111 * written to the physical medium.
112 *
113 * sync is meant to be used by code that requires physical
114 * storage (such as a file) to be in a known state For
115 * example, a class that provided a simple transaction facility
116 * might use sync to ensure that all changes to a file caused
117 * by a given transaction were recorded on a storage medium.
118 *
119 * sync only affects buffers downstream of this FileDescriptor. If
120 * any in-memory buffering is being done by the application (for
121 * example, by a BufferedOutputStream object), those buffers must
122 * be flushed into the FileDescriptor (for example, by invoking
123 * OutputStream.flush) before that data will be affected by sync.
124 *
125 * @exception SyncFailedException
126 * Thrown when the buffers cannot be flushed,
127 * or because the system cannot guarantee that all the
128 * buffers have been synchronized with physical media.
129 * @since 1.1
130 */
131 public native void sync() throws SyncFailedException;
132
133 /* This routine initializes JNI field offsets for the class */
134 private static native void initIDs();
135
136 static {
137 initIDs();
138 }
139
140 // Set up JavaIOFileDescriptorAccess in SharedSecrets
141 static {
142 sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
143 new sun.misc.JavaIOFileDescriptorAccess() {
144 public void set(FileDescriptor obj, int fd) {
145 obj.fd = fd;
146 }
147
148 public int get(FileDescriptor obj) {
149 return obj.fd;
150 }
151
152 public void setHandle(FileDescriptor obj, long handle) {
153 throw new UnsupportedOperationException();
154 }
155
156 public long getHandle(FileDescriptor obj) {
157 throw new UnsupportedOperationException();
158 }
159 }
160 );
161 }
162
163 /*
164 * Package private methods to track referents.
165 * If multiple streams point to the same FileDescriptor, we cycle
166 * through the list of all referents and call close()
167 */
168
169 /**
170 * Attach a Closeable to this FD for tracking.
171 * parent reference is added to otherParents when
172 * needed to make closeAll simpler.
173 */
174 synchronized void attach(Closeable c) {
175 if (parent == null) {
176 // first caller gets to do this
177 parent = c;
178 } else if (otherParents == null) {
179 otherParents = new ArrayList<>();
180 otherParents.add(parent);
181 otherParents.add(c);
182 } else {
183 otherParents.add(c);
184 }
185 }
186
187 /**
188 * Cycle through all Closeables sharing this FD and call
189 * close() on each one.
190 *
191 * The caller closeable gets to call close0().
192 */
193 @SuppressWarnings("try")
194 synchronized void closeAll(Closeable releaser) throws IOException {
195 if (!closed) {
196 closed = true;
197 IOException ioe = null;
198 try (Closeable c = releaser) {
199 if (otherParents != null) {
200 for (Closeable referent : otherParents) {
201 try {
202 referent.close();
203 } catch(IOException x) {
204 if (ioe == null) {
205 ioe = x;
206 } else {
207 ioe.addSuppressed(x);
208 }
209 }
210 }
211 }
212 } catch(IOException ex) {
213 /*
214 * If releaser close() throws IOException
215 * add other exceptions as suppressed.
216 */
217 if (ioe != null)
218 ex.addSuppressed(ioe);
219 ioe = ex;
220 } finally {
221 if (ioe != null)
222 throw ioe;
223 }
224 }
225 }
226 }