1/* 2 * Copyright (c) 2003, 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 26package java.io; 27 28import java.util.ArrayList; 29import java.util.List; 30import jdk.internal.misc.JavaIOFileDescriptorAccess; 31import 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 36 * open file, an open socket, or another source or sink of bytes. 37 * The main practical use for a file descriptor is to create a 38 * {@link FileInputStream} or {@link FileOutputStream} to contain it. 39 * 40 * <p>Applications should not create their own file descriptors. 41 * 42 * @author Pavani Diwanji 43 * @since 1.0 44 */ 45public final class FileDescriptor { 46 47 private int fd; 48 49 private long handle; 50 51 private Closeable parent; 52 private List<Closeable> otherParents; 53 private boolean closed; 54 55 /** 56 * true, if file is opened for appending. 57 */ 58 private boolean append; 59 60 /** 61 * Constructs an (invalid) FileDescriptor 62 * object. 63 */ 64 public /**/ FileDescriptor() { 65 fd = -1; 66 handle = -1; 67 } 68 69 static { 70 initIDs(); 71 } 72 73 // Set up JavaIOFileDescriptorAccess in SharedSecrets 74 static { 75 SharedSecrets.setJavaIOFileDescriptorAccess( 76 new JavaIOFileDescriptorAccess() { 77 public void set(FileDescriptor obj, int fd) { 78 obj.fd = fd; 79 } 80 81 public int get(FileDescriptor obj) { 82 return obj.fd; 83 } 84 85 public void setAppend(FileDescriptor obj, boolean append) { 86 obj.append = append; 87 } 88 89 public boolean getAppend(FileDescriptor obj) { 90 return obj.append; 91 } 92 93 public void setHandle(FileDescriptor obj, long handle) { 94 obj.handle = handle; 95 } 96 97 public long getHandle(FileDescriptor obj) { 98 return obj.handle; 99 } 100 } 101 ); 102 } 103 104 /** 105 * A handle to the standard input stream. Usually, this file 106 * descriptor is not used directly, but rather via the input stream 107 * known as {@code System.in}. 108 * 109 * @see java.lang.System#in 110 */ 111 public static final FileDescriptor in = standardStream(0); 112 113 /** 114 * A handle to the standard output stream. Usually, this file 115 * descriptor is not used directly, but rather via the output stream 116 * known as {@code System.out}. 117 * @see java.lang.System#out 118 */ 119 public static final FileDescriptor out = standardStream(1); 120 121 /** 122 * A handle to the standard error stream. Usually, this file 123 * descriptor is not used directly, but rather via the output stream 124 * known as {@code System.err}. 125 * 126 * @see java.lang.System#err 127 */ 128 public static final FileDescriptor err = standardStream(2); 129 130 /** 131 * Tests if this file descriptor object is valid. 132 * 133 * @return {@code true} if the file descriptor object represents a 134 * valid, open file, socket, or other active I/O connection; 135 * {@code false} otherwise. 136 */ 137 public boolean valid() { 138 return ((handle != -1) || (fd != -1)); 139 } 140 141 /** 142 * Force all system buffers to synchronize with the underlying 143 * device. This method returns after all modified data and 144 * attributes of this FileDescriptor have been written to the 145 * relevant device(s). In particular, if this FileDescriptor 146 * refers to a physical storage medium, such as a file in a file 147 * system, sync will not return until all in-memory modified copies 148 * of buffers associated with this FileDesecriptor have been 149 * written to the physical medium. 150 * 151 * sync is meant to be used by code that requires physical 152 * storage (such as a file) to be in a known state For 153 * example, a class that provided a simple transaction facility 154 * might use sync to ensure that all changes to a file caused 155 * by a given transaction were recorded on a storage medium. 156 * 157 * sync only affects buffers downstream of this FileDescriptor. If 158 * any in-memory buffering is being done by the application (for 159 * example, by a BufferedOutputStream object), those buffers must 160 * be flushed into the FileDescriptor (for example, by invoking 161 * OutputStream.flush) before that data will be affected by sync. 162 * 163 * @exception SyncFailedException 164 * Thrown when the buffers cannot be flushed, 165 * or because the system cannot guarantee that all the 166 * buffers have been synchronized with physical media. 167 * @since 1.1 168 */ 169 public native void sync() throws SyncFailedException; 170 171 /* This routine initializes JNI field offsets for the class */ 172 private static native void initIDs(); 173 174 private static native long set(int d); 175 176 private static FileDescriptor standardStream(int fd) { 177 FileDescriptor desc = new FileDescriptor(); 178 desc.handle = set(fd); 179 return desc; 180 } 181 182 /* 183 * Package private methods to track referents. 184 * If multiple streams point to the same FileDescriptor, we cycle 185 * through the list of all referents and call close() 186 */ 187 188 /** 189 * Attach a Closeable to this FD for tracking. 190 * parent reference is added to otherParents when 191 * needed to make closeAll simpler. 192 */ 193 synchronized void attach(Closeable c) { 194 if (parent == null) { 195 // first caller gets to do this 196 parent = c; 197 } else if (otherParents == null) { 198 otherParents = new ArrayList<>(); 199 otherParents.add(parent); 200 otherParents.add(c); 201 } else { 202 otherParents.add(c); 203 } 204 } 205 206 /** 207 * Cycle through all Closeables sharing this FD and call 208 * close() on each one. 209 * 210 * The caller closeable gets to call close0(). 211 */ 212 @SuppressWarnings("try") 213 synchronized void closeAll(Closeable releaser) throws IOException { 214 if (!closed) { 215 closed = true; 216 IOException ioe = null; 217 try (releaser) { 218 if (otherParents != null) { 219 for (Closeable referent : otherParents) { 220 try { 221 referent.close(); 222 } catch(IOException x) { 223 if (ioe == null) { 224 ioe = x; 225 } else { 226 ioe.addSuppressed(x); 227 } 228 } 229 } 230 } 231 } catch(IOException ex) { 232 /* 233 * If releaser close() throws IOException 234 * add other exceptions as suppressed. 235 */ 236 if (ioe != null) 237 ex.addSuppressed(ioe); 238 ioe = ex; 239 } finally { 240 if (ioe != null) 241 throw ioe; 242 } 243 } 244 } 245} 246