1 /*
2 * Copyright (c) 1995, 2012, 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 import java.util.ArrayList;
28 import java.util.List;
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 private Closeable parent;
49 private List<Closeable> otherParents;
50 private boolean closed;
51
52 /**
53 * Constructs an (invalid) FileDescriptor
54 * object.
55 */
56 public /**/ FileDescriptor() {
57 fd = -1;
58 }
59
60 private /* */ FileDescriptor(int fd) {
61 this.fd = fd;
62 }
63
64 /**
65 * A handle to the standard input stream. Usually, this file
66 * descriptor is not used directly, but rather via the input stream
67 * known as <code>System.in</code>.
68 *
69 * @see java.lang.System#in
70 */
71 public static final FileDescriptor in = new FileDescriptor(0);
72
73 /**
74 * A handle to the standard output stream. Usually, this file
75 * descriptor is not used directly, but rather via the output stream
76 * known as <code>System.out</code>.
77 * @see java.lang.System#out
78 */
79 public static final FileDescriptor out = new FileDescriptor(1);
80
81 /**
82 * A handle to the standard error stream. Usually, this file
83 * descriptor is not used directly, but rather via the output stream
84 * known as <code>System.err</code>.
85 *
86 * @see java.lang.System#err
87 */
88 public static final FileDescriptor err = new FileDescriptor(2);
89
90 /**
91 * Tests if this file descriptor object is valid.
92 *
93 * @return <code>true</code> if the file descriptor object represents a
94 * valid, open file, socket, or other active I/O connection;
95 * <code>false</code> otherwise.
96 */
97 public boolean valid() {
98 return fd != -1;
99 }
100
101 /**
102 * Force all system buffers to synchronize with the underlying
103 * device. This method returns after all modified data and
104 * attributes of this FileDescriptor have been written to the
105 * relevant device(s). In particular, if this FileDescriptor
106 * refers to a physical storage medium, such as a file in a file
107 * system, sync will not return until all in-memory modified copies
108 * of buffers associated with this FileDescriptor have been
109 * written to the physical medium.
110 *
111 * sync is meant to be used by code that requires physical
112 * storage (such as a file) to be in a known state For
113 * example, a class that provided a simple transaction facility
114 * might use sync to ensure that all changes to a file caused
115 * by a given transaction were recorded on a storage medium.
116 *
117 * sync only affects buffers downstream of this FileDescriptor. If
118 * any in-memory buffering is being done by the application (for
119 * example, by a BufferedOutputStream object), those buffers must
120 * be flushed into the FileDescriptor (for example, by invoking
121 * OutputStream.flush) before that data will be affected by sync.
122 *
123 * @exception SyncFailedException
124 * Thrown when the buffers cannot be flushed,
125 * or because the system cannot guarantee that all the
126 * buffers have been synchronized with physical media.
127 * @since JDK1.1
128 */
129 public native void sync() throws SyncFailedException;
130
131 /* This routine initializes JNI field offsets for the class */
132 private static native void initIDs();
133
134 static {
135 initIDs();
136 }
137
138 // Set up JavaIOFileDescriptorAccess in SharedSecrets
139 static {
140 sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
141 new sun.misc.JavaIOFileDescriptorAccess() {
142 public void set(FileDescriptor obj, int fd) {
143 obj.fd = fd;
144 }
145
146 public int get(FileDescriptor obj) {
147 return obj.fd;
148 }
149
150 public void setHandle(FileDescriptor obj, long handle) {
151 throw new UnsupportedOperationException();
152 }
153
154 public long getHandle(FileDescriptor obj) {
155 throw new UnsupportedOperationException();
156 }
157 }
158 );
159 }
160
161 /*
162 * Package private methods to track referents.
163 * If multiple streams point to the same FileDescriptor, we cycle
164 * through the list of all referents and call close()
165 */
166
167 /**
168 * Attach a Closeable to this FD for tracking.
169 * parent reference is added to otherParents when
170 * needed to make closeAll simpler.
171 */
172 synchronized void attach(Closeable c) {
173 if (parent == null) {
174 // first caller gets to do this
175 parent = c;
176 } else if (otherParents == null) {
177 otherParents = new ArrayList<>();
178 otherParents.add(parent);
179 otherParents.add(c);
180 } else {
181 otherParents.add(c);
182 }
183 }
184
185 /**
186 * Cycle through all Closeables sharing this FD and call
187 * close() on each one.
188 *
189 * The caller closeable gets to call close0().
190 */
191 @SuppressWarnings("try")
192 synchronized void closeAll(Closeable releaser) throws IOException {
193 if (!closed) {
194 closed = true;
195 IOException ioe = null;
196 try (Closeable c = releaser) {
197 if (otherParents != null) {
198 for (Closeable referent : otherParents) {
199 try {
200 referent.close();
201 } catch(IOException x) {
202 if (ioe == null) {
203 ioe = x;
204 } else {
205 ioe.addSuppressed(x);
206 }
207 }
208 }
209 }
210 } catch(IOException ex) {
211 /*
212 * If releaser close() throws IOException
213 * add other exceptions as suppressed.
214 */
215 if (ioe != null)
216 ex.addSuppressed(ioe);
217 ioe = ex;
218 } finally {
219 if (ioe != null)
220 throw ioe;
221 }
222 }
223 }
224 }