Source for java.io.PipedReader

   1: /* PipedReader.java -- Read portion of piped character 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., 51 Franklin Street, Fifth Floor, Boston, MA
  19: 02110-1301 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: package java.io;
  39: 
  40: // NOTE: This implementation is very similar to that of PipedInputStream.
  41: // If you fix a bug in here, chances are you should make a similar change to
  42: // the PipedInputStream code.
  43: 
  44: /**
  45:   * An input stream that reads characters from a piped writer to which it is
  46:   * connected.
  47:   * <p>
  48:   * Data is read and written to an internal buffer.  It is highly recommended
  49:   * that the <code>PipedReader</code> and connected <code>PipedWriter</code>
  50:   * be part of different threads.  If they are not, there is a possibility
  51:   * that the read and write 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 PipedReader extends Reader
  62: {
  63:   /** PipedWriter to which this is connected. Null only if this
  64:     * Reader hasn't been connected yet. */
  65:   PipedWriter source;
  66: 
  67:   /** Set to true if close() has been called on this Reader. */
  68:   boolean closed;
  69: 
  70:   /**
  71:     * The size of the internal buffer used for input/output.
  72:     */
  73:   static final int PIPE_SIZE = 2048;
  74: 
  75:   /**
  76:     * This is the internal circular buffer used for storing chars written
  77:     * to the pipe and from which chars are read by this stream
  78:     */
  79:   char[] buffer = new char[PIPE_SIZE];
  80: 
  81:   /**
  82:     * The index into buffer where the next char from the connected
  83:     * <code>PipedWriter</code> will be written. If this variable is
  84:     * equal to <code>out</code>, then the buffer is full. If set to < 0,
  85:     * the buffer is empty.
  86:     */
  87:   int in = -1;
  88: 
  89:   /**
  90:     * This index into the buffer where chars will be read from.
  91:     */
  92:   int out = 0;
  93: 
  94:   /** Buffer used to implement single-argument read/receive */
  95:   char[] read_buf = new char[1];
  96: 
  97:   /**
  98:     * Creates a new <code>PipedReader</code> that is not connected to a
  99:     * <code>PipedWriter</code>.  It must be connected before chars can
 100:     * be read from this stream.
 101:     */
 102:   public PipedReader()
 103:   {
 104:   }
 105: 
 106:   /**
 107:     * This constructor creates a new <code>PipedReader</code> and connects
 108:     * it to the passed in <code>PipedWriter</code>. The stream is then
 109:     * ready for reading.
 110:     *
 111:     * @param source The <code>PipedWriter</code> to connect this stream to
 112:     *
 113:     * @exception IOException If <code>source</code> is already connected.
 114:     */
 115:   public PipedReader(PipedWriter source) throws IOException
 116:   {
 117:     connect(source);
 118:   }
 119: 
 120:   /**
 121:     * This method connects this stream to the passed in
 122:     * <code>PipedWriter</code>.
 123:     * This stream is then ready for reading.  If this stream is already
 124:     * connected or has been previously closed, then an exception is thrown
 125:     *
 126:     * @param source The <code>PipedWriter</code> to connect this stream to
 127:     *
 128:     * @exception IOException If this PipedReader or <code>source</code>
 129:     *                        has been connected already.
 130:     */
 131:   public void connect(PipedWriter source) throws IOException
 132:   {
 133:     // The JDK (1.3) does not appear to check for a previously closed
 134:     // connection here.
 135: 
 136:     if (this.source != null || source.sink != null)
 137:       throw new IOException ("Already connected");
 138: 
 139:     source.sink = this;
 140:     this.source = source;
 141:   }
 142: 
 143:   /**
 144:     * This method is used by the connected <code>PipedWriter</code> to
 145:     * write chars into the buffer.
 146:     *
 147:     * @param buf The array containing chars to write to this stream
 148:     * @param offset The offset into the array to start writing from
 149:     * @param len The number of chars to write.
 150:     *
 151:     * @exception IOException If an error occurs
 152:     * @specnote This code should be in PipedWriter.write, but we
 153:     *           put it here in order to support that bizarre recieve(int)
 154:     *           method.
 155:     */
 156:   void receive(char[] buf, int offset, int len)
 157:     throws IOException
 158:   {
 159:     synchronized (lock)
 160:     {
 161:       if (closed)
 162:         throw new IOException ("Pipe closed");
 163: 
 164:       int bufpos = offset;
 165:       int copylen;
 166: 
 167:       while (len > 0)
 168:         {
 169:           try
 170:             {
 171:               while (in == out)
 172:                 {
 173:                   // The pipe is full. Wake up any readers and wait for them.
 174:                   lock.notifyAll();
 175:                   lock.wait();
 176:                   // The pipe could have been closed while we were waiting.
 177:                   if (closed)
 178:                     throw new IOException ("Pipe closed");
 179:                 }
 180:             }
 181:           catch (InterruptedException ix)
 182:             {
 183:               throw new InterruptedIOException ();
 184:             }
 185: 
 186:           if (in < 0) // The pipe is empty.
 187:             in = 0;
 188: 
 189:           // Figure out how many chars from buf can be copied without
 190:           // overrunning out or going past the length of the buffer.
 191:           if (in < out)
 192:             copylen = Math.min (len, out - in);
 193:           else
 194:             copylen = Math.min (len, buffer.length - in);
 195: 
 196:           // Copy chars until the pipe is filled, wrapping if necessary.
 197:           System.arraycopy(buf, bufpos, buffer, in, copylen);
 198:           len -= copylen;
 199:           bufpos += copylen;
 200:           in += copylen;
 201:           if (in == buffer.length)
 202:             in = 0;
 203:         }
 204:       // Notify readers that new data is in the pipe.
 205:       lock.notifyAll();
 206:     }
 207:   }
 208: 
 209:   /**
 210:     * This method reads chars from the stream into a caller supplied buffer.
 211:     * It starts storing chars at position <code>offset</code> into the
 212:     * buffer and
 213:     * reads a maximum of <code>len</code> chars.  Note that this method
 214:     * can actually
 215:     * read fewer than <code>len</code> chars.  The actual number of chars
 216:     * read is
 217:     * returned.  A -1 is returned to indicated that no chars can be read
 218:     * because the end of the stream was reached.  If the stream is already
 219:     * closed, a -1 will again be returned to indicate the end of the stream.
 220:     * <p>
 221:     * This method will block if no char is available to be read.
 222:     */
 223:   public int read() throws IOException
 224:   {
 225:     // Method operates by calling the multichar overloaded read method
 226:     // Note that read_buf is an internal instance variable.  I allocate it
 227:     // there to avoid constant reallocation overhead for applications that
 228:     // call this method in a loop at the cost of some unneeded overhead
 229:     // if this method is never called.
 230: 
 231:     int r = read(read_buf, 0, 1);
 232:     return r != -1 ? read_buf[0] : -1;
 233:   }
 234: 
 235:   /**
 236:     * This method reads characters from the stream into a caller supplied
 237:     * buffer. It starts storing chars at position <code>offset</code> into
 238:     * the buffer and reads a maximum of <code>len</code> chars.  Note that
 239:     * this method can actually read fewer than <code>len</code> chars.
 240:     * The actual number of chars read is
 241:     * returned.  A -1 is returned to indicated that no chars can be read
 242:     * because the end of the stream was reached - ie close() was called on the
 243:     * connected PipedWriter.
 244:     * <p>
 245:     * This method will block if no chars are available to be read.
 246:     *
 247:     * @param buf The buffer into which chars will be stored
 248:     * @param offset The index into the buffer at which to start writing.
 249:     * @param len The maximum number of chars to read.
 250:     *
 251:     * @exception IOException If <code>close()</code> was called on this Piped
 252:     *                        Reader.
 253:     */
 254:   public int read(char[] buf, int offset, int len)
 255:     throws IOException
 256:   {
 257:     synchronized (lock)
 258:     {
 259:       if (source == null)
 260:         throw new IOException ("Not connected");
 261:       if (closed)
 262:         throw new IOException ("Pipe closed");
 263: 
 264:       // Don't block if nothing was requested.
 265:       if (len == 0)
 266:         return 0;
 267: 
 268:       // If the buffer is empty, wait until there is something in the pipe
 269:       // to read.
 270:       try
 271:         {
 272:           while (in < 0)
 273:             {
 274:               if (source.closed)
 275:                 return -1;
 276:               lock.wait();
 277:             }
 278:         }
 279:       catch (InterruptedException ix)
 280:         {
 281:           throw new InterruptedIOException();
 282:         }
 283: 
 284:       int total = 0;
 285:       int copylen;
 286: 
 287:       while (true)
 288:         {
 289:           // Figure out how many chars from the pipe can be copied without
 290:           // overrunning in or going past the length of buf.
 291:           if (out < in)
 292:             copylen = Math.min (len, in - out);
 293:           else
 294:             copylen = Math.min (len, buffer.length - out);
 295: 
 296:           System.arraycopy (buffer, out, buf, offset, copylen);
 297:           offset += copylen;
 298:           len -= copylen;
 299:           out += copylen;
 300:           total += copylen;
 301: 
 302:           if (out == buffer.length)
 303:             out = 0;
 304: 
 305:           if (out == in)
 306:             {
 307:               // Pipe is now empty.
 308:               in = -1;
 309:               out = 0;
 310:             }
 311: 
 312:           // If output buffer is filled or the pipe is empty, we're done.
 313:           if (len == 0 || in == -1)
 314:             {
 315:               // Notify any waiting Writer that there is now space
 316:               // to write.
 317:               lock.notifyAll();
 318:               return total;
 319:             }
 320:         }
 321:     }
 322:   }
 323: 
 324:   public boolean ready() throws IOException
 325:   {
 326:     // The JDK 1.3 implementation does not appear to check for the closed or
 327:     // unconnected stream conditions here.  However, checking for a
 328:     // closed stream is explicitly required by the JDK 1.2 and 1.3
 329:     // documentation (for Reader.close()), so we do it.
 330: 
 331:     synchronized (lock)
 332:     {
 333:       if (closed)
 334:         throw new IOException("Pipe closed");
 335: 
 336:       if (in < 0)
 337:         return false;
 338: 
 339:       int count;
 340:       if (out < in)
 341:         count = in - out;
 342:       else
 343:         count = (buffer.length - out) - in;
 344: 
 345:       return (count > 0);
 346:     }
 347:   }
 348: 
 349:   /**
 350:   * This methods closes the stream so that no more data can be read
 351:   * from it.
 352:   *
 353:   * @exception IOException If an error occurs
 354:   */
 355:   public void close() throws IOException
 356:   {
 357:     synchronized (lock)
 358:     {
 359:       closed = true;
 360:       // Wake any thread which may be in receive() waiting to write data.
 361:       lock.notifyAll();
 362:     }
 363:   }
 364: }