1/*
2 *  Licensed to the Apache Software Foundation (ASF) under one or more
3 *  contributor license agreements.  See the NOTICE file distributed with
4 *  this work for additional information regarding copyright ownership.
5 *  The ASF licenses this file to You under the Apache License, Version 2.0
6 *  (the "License"); you may not use this file except in compliance with
7 *  the License.  You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 *  Unless required by applicable law or agreed to in writing, software
12 *  distributed under the License is distributed on an "AS IS" BASIS,
13 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 *  See the License for the specific language governing permissions and
15 *  limitations under the License.
16 */
17
18package java.io;
19
20import libcore.io.ErrnoException;
21import libcore.io.Libcore;
22import static libcore.io.OsConstants.*;
23
24/**
25 * Wraps a Unix file descriptor. It's possible to get the file descriptor used by some
26 * classes (such as {@link FileInputStream}, {@link FileOutputStream},
27 * and {@link RandomAccessFile}), and then create new streams that point to the same
28 * file descriptor.
29 */
30public final class FileDescriptor {
31
32    /**
33     * Corresponds to {@code stdin}.
34     */
35    public static final FileDescriptor in = new FileDescriptor();
36
37    /**
38     * Corresponds to {@code stdout}.
39     */
40    public static final FileDescriptor out = new FileDescriptor();
41
42    /**
43     * Corresponds to {@code stderr}.
44     */
45    public static final FileDescriptor err = new FileDescriptor();
46
47    /**
48     * The Unix file descriptor backing this FileDescriptor.
49     * A value of -1 indicates that this FileDescriptor is invalid.
50     */
51    private int descriptor = -1;
52
53    static {
54        in.descriptor = STDIN_FILENO;
55        out.descriptor = STDOUT_FILENO;
56        err.descriptor = STDERR_FILENO;
57    }
58
59    /**
60     * Constructs a new invalid FileDescriptor.
61     */
62    public FileDescriptor() {
63    }
64
65    /**
66     * Ensures that data which is buffered within the underlying implementation
67     * is written out to the appropriate device before returning.
68     */
69    public void sync() throws SyncFailedException {
70        try {
71            if (Libcore.os.isatty(this)) {
72                Libcore.os.tcdrain(this);
73            } else {
74                Libcore.os.fsync(this);
75            }
76        } catch (ErrnoException errnoException) {
77            SyncFailedException sfe = new SyncFailedException(errnoException.getMessage());
78            sfe.initCause(errnoException);
79            throw sfe;
80        }
81    }
82
83    /**
84     * Tests whether this {@code FileDescriptor} is valid.
85     */
86    public boolean valid() {
87        return descriptor != -1;
88    }
89
90    /**
91     * Returns the int fd. It's highly unlikely you should be calling this. Please discuss
92     * your needs with a libcore maintainer before using this method.
93     * @hide internal use only
94     */
95    public final int getInt$() {
96        return descriptor;
97    }
98
99    /**
100     * Sets the int fd. It's highly unlikely you should be calling this. Please discuss
101     * your needs with a libcore maintainer before using this method.
102     * @hide internal use only
103     */
104    public final void setInt$(int fd) {
105        this.descriptor = fd;
106    }
107
108    @Override public String toString() {
109        return "FileDescriptor[" + descriptor + "]";
110    }
111}
112