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 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 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 */ 48public 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} 248