1 /*
   2  * Copyright (c) 2014, 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 jdk.internal.jimage;
  27 
  28 import java.io.Closeable;
  29 import java.io.IOException;
  30 import java.io.RandomAccessFile;
  31 import java.nio.channels.FileChannel;
  32 import java.lang.reflect.Constructor;
  33 import java.lang.reflect.InvocationTargetException;
  34 
  35 /**
  36  * Supports reading a file from given positions (offsets) in the file.
  37  */
  38 
  39 public abstract class PReader implements Closeable {
  40     private final FileChannel fc;
  41 
  42     protected PReader(FileChannel fc) {
  43         this.fc = fc;
  44     }
  45 
  46     /**
  47      * Returns the {@code FileChannel}.
  48      */
  49     final FileChannel channel() {
  50         return fc;
  51     }
  52 
  53     /**
  54      * Closes this {@code PReader} and the underlying file.
  55      */
  56     @Override
  57     public final void close() throws IOException {
  58         fc.close();
  59     }
  60 
  61     /**
  62      * Returns {@code true} if this {@code PReader} and the underlying file is
  63      * open.
  64      */
  65     public final boolean isOpen() {
  66         return fc.isOpen();
  67     }
  68 
  69     /**
  70      * Returns {@code len} bytes from a given position in the file. The bytes
  71      * are returned as a byte array.
  72      *
  73      * @throws IOException if an I/O error occurs
  74      */
  75     public abstract byte[] read(int len, long position) throws IOException;
  76 
  77     /**
  78      * Opens the given file, returning a {@code PReader} to read from the file.
  79      *
  80      * @implNote Returns a {@code PReader} that supports concurrent pread operations
  81      * if possible, otherwise a simple {@code PReader} that doesn't support
  82      * concurrent operations.
  83      */
  84     static PReader open(String file) throws IOException {
  85         Class<?> clazz;
  86         try {
  87             clazz = Class.forName("jdk.internal.jimage.concurrent.ConcurrentPReader");
  88         } catch (ClassNotFoundException e) {
  89             return new SimplePReader(file);
  90         }
  91         try {
  92             Constructor<?> ctor = clazz.getConstructor(String.class);
  93             return (PReader) ctor.newInstance(file);
  94         } catch (InvocationTargetException e) {
  95             Throwable cause = e.getCause();
  96             if (cause instanceof IOException)
  97                 throw (IOException) cause;
  98             if (cause instanceof Error)
  99                 throw (Error) cause;
 100             if (cause instanceof RuntimeException)
 101                 throw (RuntimeException) cause;
 102             throw new Error(e);
 103         } catch (NoSuchMethodException | IllegalAccessException |
 104                 InstantiationException e) {
 105             throw new InternalError(e);
 106         }
 107     }
 108 }
 109 
 110 /**
 111  * Simple PReader implementation based on {@code RandomAccessFile}.
 112  *
 113  * @implNote This class cannot use FileChannel read methods to do the
 114  * positional reads because FileChannel is interruptible.
 115  */
 116 class SimplePReader extends PReader {
 117     private final RandomAccessFile raf;
 118 
 119     private SimplePReader(RandomAccessFile raf) throws IOException {
 120         super(raf.getChannel());
 121         this.raf = raf;
 122     }
 123 
 124     SimplePReader(String file) throws IOException {
 125         this(new RandomAccessFile(file, "r"));
 126     }
 127 
 128     @Override
 129     public byte[] read(int len, long position) throws IOException {
 130         synchronized (this) {
 131             byte[] bytes = new byte[len];
 132             raf.seek(position);
 133             int n = raf.read(bytes);
 134             if (n != len)
 135                 throw new InternalError("short read, not handled yet");
 136             return bytes;
 137         }
 138     }
 139 }