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 28 import android.system.ErrnoException; 29 import android.system.Os; 30 import static android.system.OsConstants.F_DUPFD_CLOEXEC; 31 32 import java.util.concurrent.atomic.AtomicInteger; 33 34 /** 35 * Instances of the file descriptor class serve as an opaque handle 36 * to the underlying machine-specific structure representing an open 37 * file, an open socket, or another source or sink of bytes. The 38 * main practical use for a file descriptor is to create a 39 * <code>FileInputStream</code> or <code>FileOutputStream</code> to 40 * contain it. 41 * <p> 42 * Applications should not create their own file descriptors. 43 * 44 * @author Pavani Diwanji 45 * @see java.io.FileInputStream 46 * @see java.io.FileOutputStream 47 * @since JDK1.0 48 */ 49 public final class FileDescriptor { 50 51 private int descriptor; 52 53 /** 54 * Constructs an (invalid) FileDescriptor 55 * object. 56 */ FileDescriptor()57 public FileDescriptor() { 58 descriptor = -1; 59 } 60 FileDescriptor(int descriptor)61 private FileDescriptor(int descriptor) { 62 this.descriptor = descriptor; 63 } 64 65 /** 66 * A handle to the standard input stream. Usually, this file 67 * descriptor is not used directly, but rather via the input stream 68 * known as <code>System.in</code>. 69 * 70 * @see java.lang.System#in 71 */ 72 public static final FileDescriptor in = dupFd(0); 73 74 /** 75 * A handle to the standard output stream. Usually, this file 76 * descriptor is not used directly, but rather via the output stream 77 * known as <code>System.out</code>. 78 * @see java.lang.System#out 79 */ 80 public static final FileDescriptor out = dupFd(1); 81 82 /** 83 * A handle to the standard error stream. Usually, this file 84 * descriptor is not used directly, but rather via the output stream 85 * known as <code>System.err</code>. 86 * 87 * @see java.lang.System#err 88 */ 89 public static final FileDescriptor err = dupFd(2); 90 91 /** 92 * Tests if this file descriptor object is valid. 93 * 94 * @return <code>true</code> if the file descriptor object represents a 95 * valid, open file, socket, or other active I/O connection; 96 * <code>false</code> otherwise. 97 */ valid()98 public boolean valid() { 99 return descriptor != -1; 100 } 101 102 /** 103 * Force all system buffers to synchronize with the underlying 104 * device. This method returns after all modified data and 105 * attributes of this FileDescriptor have been written to the 106 * relevant device(s). In particular, if this FileDescriptor 107 * refers to a physical storage medium, such as a file in a file 108 * system, sync will not return until all in-memory modified copies 109 * of buffers associated with this FileDescriptor have been 110 * written to the physical medium. 111 * 112 * sync is meant to be used by code that requires physical 113 * storage (such as a file) to be in a known state For 114 * example, a class that provided a simple transaction facility 115 * might use sync to ensure that all changes to a file caused 116 * by a given transaction were recorded on a storage medium. 117 * 118 * sync only affects buffers downstream of this FileDescriptor. If 119 * any in-memory buffering is being done by the application (for 120 * example, by a BufferedOutputStream object), those buffers must 121 * be flushed into the FileDescriptor (for example, by invoking 122 * OutputStream.flush) before that data will be affected by sync. 123 * 124 * @exception SyncFailedException 125 * Thrown when the buffers cannot be flushed, 126 * or because the system cannot guarantee that all the 127 * buffers have been synchronized with physical media. 128 * @since JDK1.1 129 */ sync()130 public native void sync() throws SyncFailedException; 131 132 /** 133 * Returns the int descriptor. It's highly unlikely you should be calling this. Please discuss 134 * your needs with a libcore maintainer before using this method. 135 * @hide internal use only 136 */ 137 // Android-added. getInt$()138 public final int getInt$() { 139 return descriptor; 140 } 141 142 /** 143 * Sets the int descriptor. It's highly unlikely you should be calling this. Please discuss 144 * your needs with a libcore maintainer before using this method. 145 * @hide internal use only 146 */ 147 // Android-added. setInt$(int fd)148 public final void setInt$(int fd) { 149 this.descriptor = fd; 150 } 151 152 /** 153 * @hide internal use only 154 */ 155 // Android-added. isSocket$()156 public boolean isSocket$() { 157 return isSocket(descriptor); 158 } 159 160 // Android-added. dupFd(int fd)161 private static FileDescriptor dupFd(int fd) { 162 try { 163 return new FileDescriptor(Os.fcntlInt(new FileDescriptor(fd), F_DUPFD_CLOEXEC, 0)); 164 } catch (ErrnoException e) { 165 throw new RuntimeException(e); 166 } 167 } 168 isSocket(int descriptor)169 private static native boolean isSocket(int descriptor); 170 171 } 172