1 /*
2 * Copyright (c) 1995, 2015, 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 import jdk.internal.misc.JavaIOFileDescriptorAccess;
31 import jdk.internal.misc.SharedSecrets;
32
33 /**
34 * Instances of the file descriptor class serve as an opaque handle
35 * to the underlying machine-specific structure representing an open
36 * file, an open socket, or another source or sink of bytes. The
37 * main practical use for a file descriptor is to create a
38 * <code>FileInputStream</code> or <code>FileOutputStream</code> to
39 * contain it.
40 * <p>
41 * Applications should not create their own file descriptors.
42 *
43 * @author Pavani Diwanji
44 * @see java.io.FileInputStream
45 * @see java.io.FileOutputStream
46 * @since 1.0
47 */
48 public final class FileDescriptor {
49
50 private int fd;
51
52 private Closeable parent;
53 private List<Closeable> otherParents;
54 private boolean closed;
55
56 /**
57 * true, if file is opened for appending.
58 */
59 private boolean append;
60
61 /**
62 * Constructs an (invalid) FileDescriptor
63 * object.
64 */
65 public FileDescriptor() {
66 fd = -1;
67 }
68
69 private FileDescriptor(int fd) {
70 this.fd = fd;
71 this.append = getAppend(fd);
72 }
73
74 /**
75 * A handle to the standard input stream. Usually, this file
76 * descriptor is not used directly, but rather via the input stream
77 * known as <code>System.in</code>.
78 *
79 * @see java.lang.System#in
80 */
81 public static final FileDescriptor in = new FileDescriptor(0);
82
83 /**
84 * A handle to the standard output stream. Usually, this file
85 * descriptor is not used directly, but rather via the output stream
86 * known as <code>System.out</code>.
87 * @see java.lang.System#out
88 */
89 public static final FileDescriptor out = new FileDescriptor(1);
90
91 /**
92 * A handle to the standard error stream. Usually, this file
93 * descriptor is not used directly, but rather via the output stream
94 * known as <code>System.err</code>.
95 *
96 * @see java.lang.System#err
97 */
98 public static final FileDescriptor err = new FileDescriptor(2);
99
100 /**
101 * Tests if this file descriptor object is valid.
102 *
103 * @return <code>true</code> if the file descriptor object represents a
104 * valid, open file, socket, or other active I/O connection;
105 * <code>false</code> otherwise.
106 */
107 public boolean valid() {
108 return fd != -1;
109 }
110
111 /**
112 * Force all system buffers to synchronize with the underlying
113 * device. This method returns after all modified data and
114 * attributes of this FileDescriptor have been written to the
115 * relevant device(s). In particular, if this FileDescriptor
116 * refers to a physical storage medium, such as a file in a file
117 * system, sync will not return until all in-memory modified copies
118 * of buffers associated with this FileDescriptor have been
119 * written to the physical medium.
120 *
121 * sync is meant to be used by code that requires physical
122 * storage (such as a file) to be in a known state For
123 * example, a class that provided a simple transaction facility
124 * might use sync to ensure that all changes to a file caused
125 * by a given transaction were recorded on a storage medium.
126 *
127 * sync only affects buffers downstream of this FileDescriptor. If
128 * any in-memory buffering is being done by the application (for
129 * example, by a BufferedOutputStream object), those buffers must
130 * be flushed into the FileDescriptor (for example, by invoking
131 * OutputStream.flush) before that data will be affected by sync.
132 *
133 * @exception SyncFailedException
134 * Thrown when the buffers cannot be flushed,
135 * or because the system cannot guarantee that all the
136 * buffers have been synchronized with physical media.
137 * @since 1.1
138 */
139 public native void sync() throws SyncFailedException;
140
141 /* This routine initializes JNI field offsets for the class */
142 private static native void initIDs();
143
144 static {
145 initIDs();
146 }
147
148 // Set up JavaIOFileDescriptorAccess in SharedSecrets
149 static {
150 SharedSecrets.setJavaIOFileDescriptorAccess(
151 new JavaIOFileDescriptorAccess() {
152 public void set(FileDescriptor obj, int fd) {
153 obj.fd = fd;
154 }
155
156 public int get(FileDescriptor obj) {
157 return obj.fd;
158 }
159
160 public void setAppend(FileDescriptor obj, boolean append) {
161 obj.append = append;
162 }
163
164 public boolean getAppend(FileDescriptor obj) {
165 return obj.append;
166 }
167
168 public void setHandle(FileDescriptor obj, long handle) {
169 throw new UnsupportedOperationException();
170 }
171
172 public long getHandle(FileDescriptor obj) {
173 throw new UnsupportedOperationException();
174 }
175 }
176 );
177 }
178
179 /**
180 * Returns true, if the file was opened for appending.
181 */
182 private static native boolean getAppend(int fd);
183
184 /*
185 * Package private methods to track referents.
186 * If multiple streams point to the same FileDescriptor, we cycle
187 * through the list of all referents and call close()
188 */
189
190 /**
191 * Attach a Closeable to this FD for tracking.
192 * parent reference is added to otherParents when
193 * needed to make closeAll simpler.
194 */
195 synchronized void attach(Closeable c) {
196 if (parent == null) {
197 // first caller gets to do this
198 parent = c;
199 } else if (otherParents == null) {
200 otherParents = new ArrayList<>();
201 otherParents.add(parent);
202 otherParents.add(c);
203 } else {
204 otherParents.add(c);
205 }
206 }
207
208 /**
209 * Cycle through all Closeables sharing this FD and call
210 * close() on each one.
211 *
212 * The caller closeable gets to call close0().
213 */
214 @SuppressWarnings("try")
215 synchronized void closeAll(Closeable releaser) throws IOException {
216 if (!closed) {
217 closed = true;
218 IOException ioe = null;
219 try (releaser) {
220 if (otherParents != null) {
221 for (Closeable referent : otherParents) {
222 try {
223 referent.close();
224 } catch(IOException x) {
225 if (ioe == null) {
226 ioe = x;
227 } else {
228 ioe.addSuppressed(x);
229 }
230 }
231 }
232 }
233 } catch(IOException ex) {
234 /*
235 * If releaser close() throws IOException
236 * add other exceptions as suppressed.
237 */
238 if (ioe != null)
239 ex.addSuppressed(ioe);
240 ioe = ex;
241 } finally {
242 if (ioe != null)
243 throw ioe;
244 }
245 }
246 }
247 }