libjava/java/io/PipedInputStream.java

   1 /* PipedInputStream.java -- Read portion of piped streams.
   2    Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 // NOTE: This implementation is very similar to that of PipedReader.  If you
  39 // fix a bug in here, chances are you should make a similar change to the
  40 // PipedReader code.
  41
  42 package java.io;
  43
  44 /**
  45   * An input stream that reads its bytes from an output stream
  46   * to which it is connected.
  47   * <p>
  48   * Data is read and written to an internal buffer.  It is highly recommended
  49   * that the <code>PipedInputStream</code> and connected <code>PipedOutputStream</code>
  50   * be part of different threads.  If they are not, the read and write
  51   * operations could deadlock their thread.
  52   *
  53   * @specnote The JDK implementation appears to have some undocumented
  54   *           functionality where it keeps track of what thread is writing
  55   *           to pipe and throws an IOException if that thread susequently
  56   *           dies. This behaviour seems dubious and unreliable - we don't
  57   *           implement it.
  58   *
  59   * @author Aaron M. Renn (arenn@urbanophile.com)
  60   */
  61 public class PipedInputStream extends InputStream
  62 {
  63   /** PipedOutputStream to which this is connected. Null only if this
  64     * InputStream hasn't been connected yet. */
  65   PipedOutputStream source;
  66
  67   /** Set to true if close() has been called on this InputStream. */
  68   boolean closed;
  69
  70
  71   /**
  72    * The size of the internal buffer used for input/output.
  73    */
  74   /* The "Constant Field Values" Javadoc of the Sun J2SE 1.4
  75    * specifies 1024.
  76    */
  77   protected static final int PIPE_SIZE = 1024;
  78
  79
  80   /**
  81     * This is the internal circular buffer used for storing bytes written
  82     * to the pipe and from which bytes are read by this stream
  83     */
  84   protected byte[] buffer = new byte[PIPE_SIZE];
  85
  86   /**
  87     * The index into buffer where the next byte from the connected
  88     * <code>PipedOutputStream</code> will be written. If this variable is
  89     * equal to <code>out</code>, then the buffer is full. If set to < 0,
  90     * the buffer is empty.
  91     */
  92   protected int in = -1;
  93
  94   /**
  95     * This index into the buffer where bytes will be read from.
  96     */
  97   protected int out = 0;
  98
  99   /** Buffer used to implement single-argument read/receive */
 100   private byte[] read_buf = new byte[1];
 101
 102   /**
 103     * Creates a new <code>PipedInputStream</code> that is not connected to a
 104     * <code>PipedOutputStream</code>.  It must be connected before bytes can
 105     * be read from this stream.
 106     */
 107   public PipedInputStream()
 108   {
 109   }
 110
 111   /**
 112     * This constructor creates a new <code>PipedInputStream</code> and connects
 113     * it to the passed in <code>PipedOutputStream</code>. The stream is then
 114     * ready for reading.
 115     *
 116     * @param source The <code>PipedOutputStream</code> to connect this stream to
 117     *
 118     * @exception IOException If <code>source</code> is already connected.
 119     */
 120   public PipedInputStream(PipedOutputStream source) throws IOException
 121   {
 122     connect(source);
 123   }
 124
 125   /**
 126     * This method connects this stream to the passed in <code>PipedOutputStream</code>.
 127     * This stream is then ready for reading.  If this stream is already
 128     * connected or has been previously closed, then an exception is thrown
 129     *
 130     * @param src The <code>PipedOutputStream</code> to connect this stream to
 131     *
 132     * @exception IOException If this PipedInputStream or <code>source</code>
 133     *                        has been connected already.
 134     */
 135   public void connect(PipedOutputStream source) throws IOException
 136   {
 137     // The JDK (1.3) does not appear to check for a previously closed
 138     // connection here.
 139
 140     if (this.source != null || source.sink != null)
 141       throw new IOException ("Already connected");
 142
 143     source.sink = this;
 144     this.source = source;
 145   }
 146
 147   /**
 148   * This method receives a byte of input from the source PipedOutputStream.
 149   * If the internal circular buffer is full, this method blocks.
 150   *
 151   * @param byte_received The byte to write to this stream
 152   *
 153   * @exception IOException if error occurs
 154   * @specnote Weird. This method must be some sort of accident.
 155   */
 156   protected synchronized void receive(int b) throws IOException
 157   {
 158     read_buf[0] = (byte) (b & 0xff);
 159     receive (read_buf, 0, 1);
 160   }
 161
 162   /**
 163     * This method is used by the connected <code>PipedOutputStream</code> to
 164     * write bytes into the buffer.
 165     *
 166     * @param buf The array containing bytes to write to this stream
 167     * @param offset The offset into the array to start writing from
 168     * @param len The number of bytes to write.
 169     *
 170     * @exception IOException If an error occurs
 171     * @specnote This code should be in PipedOutputStream.write, but we
 172     *           put it here in order to support that bizarre recieve(int)
 173     *           method.
 174     */
 175   synchronized void receive(byte[] buf, int offset, int len)
 176     throws IOException
 177   {
 178     if (closed)
 179       throw new IOException ("Pipe closed");
 180
 181     int bufpos = offset;
 182     int copylen;
 183
 184     while (len > 0)
 185       {
 186         try
 187           {
 188             while (in == out)
 189               {
 190                 // The pipe is full. Wake up any readers and wait for them.
 191                 notifyAll();
 192                 wait();
 193                 // The pipe could have been closed while we were waiting.
 194                 if (closed)
 195                   throw new IOException ("Pipe closed");
 196               }
 197           }
 198         catch (InterruptedException ix)
 199           {
 200             throw new InterruptedIOException ();
 201           }
 202
 203         if (in < 0) // The pipe is empty.
 204           in = 0;
 205
 206         // Figure out how many bytes from buf can be copied without
 207         // overrunning out or going past the length of the buffer.
 208         if (in < out)
 209           copylen = Math.min (len, out - in);
 210         else
 211           copylen = Math.min (len, buffer.length - in);
 212
 213         // Copy bytes until the pipe is filled, wrapping if necessary.
 214         System.arraycopy(buf, bufpos, buffer, in, copylen);
 215         len -= copylen;
 216         bufpos += copylen;
 217         in += copylen;
 218         if (in == buffer.length)
 219           in = 0;
 220       }
 221     // Notify readers that new data is in the pipe.
 222     notifyAll();
 223   }
 224
 225   /**
 226     * This method reads bytes from the stream into a caller supplied buffer.
 227     * It starts storing bytes at position <code>offset</code> into the buffer and
 228     * reads a maximum of <code>len</code> bytes.  Note that this method can actually
 229     * read fewer than <code>len</code> bytes.  The actual number of bytes read is
 230     * returned.  A -1 is returned to indicated that no bytes can be read
 231     * because the end of the stream was reached.  If the stream is already
 232     * closed, a -1 will again be returned to indicate the end of the stream.
 233     * <p>
 234     * This method will block if no bytes are available to be read.
 235     *
 236     * @param buf The buffer into which bytes will be stored
 237     * @param offset The index into the buffer at which to start writing.
 238     * @param len The maximum number of bytes to read.
 239     */
 240   public int read() throws IOException
 241   {
 242     // Method operates by calling the multibyte overloaded read method
 243     // Note that read_buf is an internal instance variable.  I allocate it
 244     // there to avoid constant reallocation overhead for applications that
 245     // call this method in a loop at the cost of some unneeded overhead
 246     // if this method is never called.
 247
 248     int r = read(read_buf, 0, 1);
 249
 250     if (r == -1)
 251       return -1;
 252     else
 253       return read_buf[0];
 254   }
 255
 256   /**
 257     * This method reads bytes from the stream into a caller supplied buffer.
 258     * It starts storing bytes at position <code>offset</code> into the buffer and
 259     * reads a maximum of <code>len</code> bytes.  Note that this method can actually
 260     * read fewer than <code>len</code> bytes.  The actual number of bytes read is
 261     * returned.  A -1 is returned to indicated that no bytes can be read
 262     * because the end of the stream was reached - ie close() was called on the
 263     * connected PipedOutputStream.
 264     * <p>
 265     * This method will block if no bytes are available to be read.
 266     *
 267     * @param buf The buffer into which bytes will be stored
 268     * @param offset The index into the buffer at which to start writing.
 269     * @param len The maximum number of bytes to read.
 270     *
 271     * @exception IOException If <code>close()/code> was called on this Piped
 272     *                        InputStream.
 273     */
 274   public synchronized int read(byte[] buf, int offset, int len)
 275     throws IOException
 276   {
 277     if (source == null)
 278       throw new IOException ("Not connected");
 279     if (closed)
 280       throw new IOException ("Pipe closed");
 281
 282     // If the buffer is empty, wait until there is something in the pipe
 283     // to read.
 284     try
 285       {
 286         while (in < 0)
 287           {
 288             if (source.closed)
 289               return -1;
 290             wait();
 291           }
 292       }
 293     catch (InterruptedException ix)
 294       {
 295         throw new InterruptedIOException();
 296       }
 297
 298     int total = 0;
 299     int copylen;
 300
 301     while (true)
 302       {
 303         // Figure out how many bytes from the pipe can be copied without
 304         // overrunning in or going past the length of buf.
 305         if (out < in)
 306           copylen = Math.min (len, in - out);
 307         else
 308           copylen = Math.min (len, buffer.length - out);
 309
 310         System.arraycopy (buffer, out, buf, offset, copylen);
 311         offset += copylen;
 312         len -= copylen;
 313         out += copylen;
 314         total += copylen;
 315
 316         if (out == buffer.length)
 317           out = 0;
 318
 319         if (out == in)
 320           {
 321             // Pipe is now empty.
 322             in = -1;
 323             out = 0;
 324           }
 325
 326         // If output buffer is filled or the pipe is empty, we're done.
 327         if (len == 0 || in == -1)
 328           {
 329             // Notify any waiting outputstream that there is now space
 330             // to write.
 331             notifyAll();
 332             return total;
 333           }
 334       }
 335   }
 336
 337   /**
 338     * This method returns the number of bytes that can be read from this stream
 339     * before blocking could occur.  This is the number of bytes that are
 340     * currently unread in the internal circular buffer.  Note that once this
 341     * many additional bytes are read, the stream may block on a subsequent
 342     * read, but it not guaranteed to block.
 343     *
 344     * @return The number of bytes that can be read before blocking might occur
 345     *
 346     * @exception IOException If an error occurs
 347     */
 348   public synchronized int available() throws IOException
 349   {
 350     // The JDK 1.3 implementation does not appear to check for the closed or
 351     // unconnected stream conditions here.
 352
 353     if (in < 0)
 354       return 0;
 355     else if (out < in)
 356       return in - out;
 357     else
 358       return (buffer.length - out) + in;
 359   }
 360
 361   /**
 362   * This methods closes the stream so that no more data can be read
 363   * from it.
 364   *
 365   * @exception IOException If an error occurs
 366   */
 367   public synchronized void close() throws IOException
 368   {
 369     closed = true;
 370     // Wake any thread which may be in receive() waiting to write data.
 371     notifyAll();
 372   }
 373 }