1 /*
2 * Copyright (c) 2003, 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
30 /**
31 * Instances of the file descriptor class serve as an opaque handle
32 * to the underlying machine-specific structure representing an
33 * open file, an open socket, or another source or sink of bytes.
34 * The main practical use for a file descriptor is to create a
35 * {@link FileInputStream} or {@link FileOutputStream} to contain it.
36 *
37 * <p>Applications should not create their own file descriptors.
38 *
39 * @author Pavani Diwanji
40 * @since JDK1.0
41 */
42 public final class FileDescriptor {
43
44 private int fd;
45
46 private long handle;
47
48 private Closeable parent;
49 private ArrayList<Closeable> otherParents;
50 boolean closed = false;
51
52 /**
53 * Constructs an (invalid) FileDescriptor
54 * object.
55 */
56 public /**/ FileDescriptor() {
57 fd = -1;
58 handle = -1;
59 }
60
61 static {
62 initIDs();
63 }
64
65 // Set up JavaIOFileDescriptorAccess in SharedSecrets
66 static {
67 sun.misc.SharedSecrets.setJavaIOFileDescriptorAccess(
68 new sun.misc.JavaIOFileDescriptorAccess() {
69 public void set(FileDescriptor obj, int fd) {
70 obj.fd = fd;
71 }
72
73 public int get(FileDescriptor obj) {
74 return obj.fd;
75 }
76
77 public void setHandle(FileDescriptor obj, long handle) {
78 obj.handle = handle;
79 }
80
81 public long getHandle(FileDescriptor obj) {
82 return obj.handle;
83 }
84 }
85 );
86 }
87
88 /**
89 * A handle to the standard input stream. Usually, this file
90 * descriptor is not used directly, but rather via the input stream
91 * known as {@code System.in}.
92 *
93 * @see java.lang.System#in
94 */
95 public static final FileDescriptor in = standardStream(0);
96
97 /**
98 * A handle to the standard output stream. Usually, this file
99 * descriptor is not used directly, but rather via the output stream
100 * known as {@code System.out}.
101 * @see java.lang.System#out
102 */
103 public static final FileDescriptor out = standardStream(1);
104
105 /**
106 * A handle to the standard error stream. Usually, this file
107 * descriptor is not used directly, but rather via the output stream
108 * known as {@code System.err}.
109 *
110 * @see java.lang.System#err
111 */
112 public static final FileDescriptor err = standardStream(2);
113
114 /**
115 * Tests if this file descriptor object is valid.
116 *
117 * @return {@code true} if the file descriptor object represents a
118 * valid, open file, socket, or other active I/O connection;
119 * {@code false} otherwise.
120 */
121 public boolean valid() {
122 return ((handle != -1) || (fd != -1));
123 }
124
125 /**
126 * Force all system buffers to synchronize with the underlying
127 * device. This method returns after all modified data and
128 * attributes of this FileDescriptor have been written to the
129 * relevant device(s). In particular, if this FileDescriptor
130 * refers to a physical storage medium, such as a file in a file
131 * system, sync will not return until all in-memory modified copies
132 * of buffers associated with this FileDesecriptor have been
133 * written to the physical medium.
134 *
135 * sync is meant to be used by code that requires physical
136 * storage (such as a file) to be in a known state For
137 * example, a class that provided a simple transaction facility
138 * might use sync to ensure that all changes to a file caused
139 * by a given transaction were recorded on a storage medium.
140 *
141 * sync only affects buffers downstream of this FileDescriptor. If
142 * any in-memory buffering is being done by the application (for
143 * example, by a BufferedOutputStream object), those buffers must
144 * be flushed into the FileDescriptor (for example, by invoking
145 * OutputStream.flush) before that data will be affected by sync.
146 *
147 * @exception SyncFailedException
148 * Thrown when the buffers cannot be flushed,
149 * or because the system cannot guarantee that all the
150 * buffers have been synchronized with physical media.
151 * @since JDK1.1
152 */
153 public native void sync() throws SyncFailedException;
154
155 /* This routine initializes JNI field offsets for the class */
156 private static native void initIDs();
157
158 private static native long set(int d);
159
160 private static FileDescriptor standardStream(int fd) {
161 FileDescriptor desc = new FileDescriptor();
162 desc.handle = set(fd);
163 return desc;
164 }
165
166 /*
167 * Package private methods to track referents.
168 * If multiple streams point to the same FileDescriptor, we cycle
169 * through the list of all referents and call close()
170 */
171
172 /*
173 * attach a Closeable to this FD for tracking
174 */
175 void attach(Closeable c) {
176 synchronized (this) {
177 if (parent == null) {
178 // constructor gets to do this
179 parent = c;
180 } else if (otherParents == null) {
181 otherParents = new ArrayList<>();
182 otherParents.add(parent);
183 otherParents.add(c);
184 } else {
185 otherParents.add(c);
186 }
187 }
188 }
189
190 /*
191 * Cycle through all Closeables sharing this FD and call
192 * close() on each one.
193 *
194 * The caller closeable gets to call close0().
195 */
196 @SuppressWarnings("try")
197 synchronized void closeAll(Closeable releaser) throws IOException {
198 if (!closed) {
199 closed = true;
200 IOException ioe = null;
201 try (Closeable c = releaser) {
202 if (otherParents != null) {
203 for (Closeable referent : otherParents) {
204 try {
205 referent.close();
206 } catch(IOException x) {
207 if (ioe == null) {
208 ioe = x;
209 } else {
210 ioe.addSuppressed(x);
211 }
212 }
213 }
214 }
215 } catch(IOException ex) {
216 // if releaser close() throws IOException
217 // add other exceptions as suppressed
218 if (ioe != null) {
219 ex.addSuppressed(ioe);
220 }
221 ioe = ex;
222 } finally {
223 if (ioe != null) {
224 throw ioe;
225 }
226 }
227 }
228 }
229 }