uk.ac.gla.dcs.renaissance.ir
Class StringBufferReader

java.lang.Object
  java.io.Reader
      uk.ac.gla.dcs.renaissance.ir.StringBufferReader

All Implemented Interfaces:

Closeable, Readable

public class StringBufferReader
extends Reader

A non-blocking Reader for reading the text that appears in a shared StringBuffer.

This class in intended to be thread-safe, and to be used both from inside and outside a vat. When used in conjunction with StringWriter or our own StringBufferWriter, the pair is like a non-blocking variant of PipedReader/PipedWriter. The sharing must be set up at creation time, as a StringBufferReader encapsulates its StringBuffer.

In order to be non-blocking, we make the following change to the Reader contract: If a read(..) is attempted on a non-ready StringBufferReader, it will throw an IOException, rather than blocking or returning zero.

In order to be thread-safe, it uses the StringBuffer as its Reader.lock.

This class does no newline conversion. This should normally be done by the object that writes into the shared StringBuffer.

Author:

Mark S. Miller, Terry Stanley

Field Summary

Fields inherited from class java.io.Reader

lock

Constructor Summary

StringBufferReader(StringBuffer buf)
Makes a Reader for reading from 'buf'

Method Summary

int	available() How many characters are immediately available? If the buffer is empty, then give the filler one chance and try again.
void	close()
boolean	isDone() Are we at end-of-stream?
void	mark(int readAheadLimit) readAheadLimit is ignored
int	read(char[] cbuf, int off, int len) Reads up to len chars, as many as it can without blocking.
Character	readChar() Returns the next available character, or null at end of file.
String	readReady() Returns as much as is available, or null at end-of-stream.
String	readString(int size) Reads no more than 'size' characters from the file, and return them as a String.
String	readText() Reads everything else and returns it.
boolean	ready() True if either at least one character is available, or we're at the end-of-stream.
void	reset()

Methods inherited from class java.io.Reader

markSupported, read, read, read, skip

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

StringBufferReader

public StringBufferReader(StringBuffer buf)

Makes a Reader for reading from 'buf'

Method Detail

close

public void close()
           throws IOException

Specified by:

close in interface Closeable

Specified by:

close in class Reader

Throws:

IOException

available

public int available()
              throws IOException

How many characters are immediately available? If the buffer is empty, then give the filler one chance and try again. If instead you want to know the largest number of characters that are available, and buffer then as a result, then call fill() first.

Currently, this entire operation is performed with 'lock' held. XXX Should we release 'lock' around the call to myOptFiller?

Throws:

IOException

ready

public boolean ready()
              throws IOException

True if either at least one character is available, or we're at the end-of-stream.

Overrides:

ready in class Reader

Throws:

IOException

isDone

public boolean isDone()
               throws IOException

Are we at end-of-stream?

Throws:

IOException

read

public int read(char[] cbuf,
                int off,
                int len)
         throws IOException

Reads up to len chars, as many as it can without blocking.

If it can't read even a single char without blocking, throw an IOException rather than blocking or returning 0.

Specified by:

read in class Reader

Throws:

IOException

mark

public void mark(int readAheadLimit)
          throws IOException

readAheadLimit is ignored

Overrides:

mark in class Reader

Throws:

IOException

reset

public void reset()
           throws IOException

Overrides:

reset in class Reader

Throws:

IOException

readChar

public Character readChar()
                   throws IOException

Returns the next available character, or null at end of file.

If nothing is currently available, throws rather than blocking or returning -1.

Throws:

IOException

readString

public String readString(int size)
                  throws IOException

Reads no more than 'size' characters from the file, and return them as a String. If at end-of-file, return null.

Throws:

IOException

readReady

public String readReady()
                 throws IOException

Returns as much as is available, or null at end-of-stream.

If nothing is currently available, return "" rather than throwing.

Throws:

IOException

readText

public String readText()
                throws IOException

Reads everything else and returns it.

If everything else isn't yet available, then throws rather than blocking or returning something funny, but characters have still been consumed anyway. If this doesn't suit you, use mark() and reset() to protect yourself.

Throws:

IOException