org.barracudamvc.plankton.io
Class BetterPipedReader

java.lang.Object
  extended by java.io.Reader
      extended by org.barracudamvc.plankton.io.BetterPipedReader
All Implemented Interfaces:
Closeable, Readable

public class BetterPipedReader
extends Reader

This class is based on Sun's PipedReader. It attempts to address 2 deficiencies in the Sun implementation: the PIPE_SIZE is configurable, and if we get a dewadlock on the writer (because the pipe size has been reached) then the writer will timeout after a certain amount of time. This is important in a servlet environment, where one request may start a writer pumping data into the sink, but you have no guarantee that anyone is going to actually read the data from the sink. Using the Sun implementation, the writer deadlocks and that thread is completely out of action for the duration...not very robust behavior for a servlet environment. This implementation will gracefully timeout, allowing the thread to complete and be returned to the servlet container for further use. It should also be noted that this implementation supports the notion of a Pausable controller, which if present will block the writer (up to but not exceeding the timeout period) while the parent controller isPaused(). Note that we completely reimplement these classes because the Sun classes weren't really designed to be extended (grrr).

Since:
csc_031204_1
Author:
Christian Cryder [christianc@granitepeaks.com]

Field Summary
protected  boolean closedByReader
           
protected  boolean closedByWriter
           
protected  boolean connected
           
static int DEFAULT_PIPE_SIZE
          The default (global) size of the pipe's circular input buffer.
static int DEFAULT_TIMEOUT
          The default (global) timeout (in millis)
protected  int in
          The index of the position in the circular buffer at which the next character of data will be stored when received from the connected piped writer.
protected static org.apache.log4j.Logger logger
           
protected  boolean notifiedFirst
           
protected  int out
          The index of the position in the circular buffer at which the next character of data will be read by this piped reader.
protected  Pausable pausable
           
protected  int pipeSize
          The pipe size for this particular circular input buffer (defaults to DEFAULT_PIPE_SIZE)
protected  Thread readSide
           
protected  StringBuffer sbuffer
          The circular buffer into which incoming data is placed.
protected  int timeout
          The timeout for this particular pipe reader (defaults to DEFAULT_TIMEOUT)
protected  Thread writeSide
           
 
Fields inherited from class java.io.Reader
lock
 
Constructor Summary
BetterPipedReader()
          Creates a BetterPipedReader that is not yet connected.
BetterPipedReader(BetterPipedWriter src)
          Creates a BetterPipedReader and automatically connect it to the piped writer src.
BetterPipedReader(Pausable ipausable, int ipipeSize)
          Creates a BetterPipedReader that is not yet connected, specifying a custom pipe size.
 
Method Summary
 void close()
          Closes this piped stream and releases any system resources associated with the stream.
 void connect(BetterPipedWriter src)
          Causes this piped reader to be connected to the piped writer src.
 Pausable getPausable()
          get the Pausable controller
 int getPipeSize()
          get the pipe size
 int getPipeTimeout()
          get the timeout setting.
 int read()
          Reads the next character of data from this piped stream.
 int read(char[] cbuf, int off, int len)
          Reads up to len characters of data from this piped stream into an array of characters.
 boolean ready()
          Tell whether this stream is ready to be read.
protected  void receive(char[] c, int off, int len)
          Receives data into an array of characters.
protected  void receive(int c)
          Receives a char of data.
protected  void receivedFirst()
          Notifies all waiting threads that we have started to receive data
protected  void receivedLast()
          Notifies all waiting threads that the last character of data has been received.
 void setPausable(Pausable ipausable)
          set the Pausable controller (null indicates the pipe can't be paused).
 void setPipeSize(int ipipeSize)
          set the pipe size.
 void setPipeTimeout(int itimeout)
          set the timeout (you may call this at any time).
 
Methods inherited from class java.io.Reader
mark, markSupported, read, read, reset, skip
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

logger

protected static final org.apache.log4j.Logger logger

closedByWriter

protected boolean closedByWriter

closedByReader

protected boolean closedByReader

connected

protected boolean connected

notifiedFirst

protected boolean notifiedFirst

pausable

protected Pausable pausable

readSide

protected Thread readSide

writeSide

protected Thread writeSide

DEFAULT_PIPE_SIZE

public static int DEFAULT_PIPE_SIZE
The default (global) size of the pipe's circular input buffer.


pipeSize

protected int pipeSize
The pipe size for this particular circular input buffer (defaults to DEFAULT_PIPE_SIZE)


DEFAULT_TIMEOUT

public static int DEFAULT_TIMEOUT
The default (global) timeout (in millis)


timeout

protected int timeout
The timeout for this particular pipe reader (defaults to DEFAULT_TIMEOUT)


sbuffer

protected StringBuffer sbuffer
The circular buffer into which incoming data is placed. This buffer is not actually initialized until you connect, to take advantage of any configuration changes to the pipe size


in

protected int in
The index of the position in the circular buffer at which the next character of data will be stored when received from the connected piped writer. in<0 implies the buffer is empty, in==out implies the buffer is full


out

protected int out
The index of the position in the circular buffer at which the next character of data will be read by this piped reader.

Constructor Detail

BetterPipedReader

public BetterPipedReader()
Creates a BetterPipedReader that is not yet connected. It must be manually connected to a BetterPipedWriter before being used.

See Also:
connect(org.barracudamvc.plankton.io.BetterPipedWriter), BetterPipedWriter.connect(org.barracudamvc.plankton.io.BetterPipedReader)

BetterPipedReader

public BetterPipedReader(Pausable ipausable,
                         int ipipeSize)
Creates a BetterPipedReader that is not yet connected, specifying a custom pipe size. It must be manually connected to a BetterPipedWriter before being used.

Parameters:
pipeSize - the specific pipe size of the circular buffer
See Also:
connect(org.barracudamvc.plankton.io.BetterPipedWriter), BetterPipedWriter.connect(org.barracudamvc.plankton.io.BetterPipedReader)

BetterPipedReader

public BetterPipedReader(BetterPipedWriter src)
                  throws IOException
Creates a BetterPipedReader and automatically connect it to the piped writer src. Data written to src will then be available as input from this stream. Note that if you use this method, calls to setPipeSize will have no effect (because the circular buffer has already been initialized when the connection was made).

Parameters:
src - the stream to connect to.
Throws:
IOException - if an I/O error occurs.
Method Detail

setPipeSize

public void setPipeSize(int ipipeSize)
set the pipe size. You want to do this before calling connect (otherwise the default pipe size will be used).


getPipeSize

public int getPipeSize()
get the pipe size


setPipeTimeout

public void setPipeTimeout(int itimeout)
set the timeout (you may call this at any time). A value less < 0 indicates no timeout.


getPipeTimeout

public int getPipeTimeout()
get the timeout setting. A value less < 0 indicates no timeout.


setPausable

public void setPausable(Pausable ipausable)
set the Pausable controller (null indicates the pipe can't be paused). Pausing a pipe effectively blocks the write process for the pipe timeout duration - thus preventing the pipe from filling up before you want it to


getPausable

public Pausable getPausable()
get the Pausable controller


connect

public void connect(BetterPipedWriter src)
             throws IOException
Causes this piped reader to be connected to the piped writer src. If this object is already connected to some other piped writer, an IOException is thrown.

If src is an unconnected piped writer and snk is an unconnected piped reader, they may be connected by either the call:

snk.connect(src) 

or the call:

src.connect(snk) 

The two calls have the same effect.

Parameters:
src - The piped writer to connect to.
Throws:
IOException - if an I/O error occurs.

receive

protected void receive(int c)
                throws IOException
Receives a char of data. This method will block if no input is available, and then timeout if the PIPE_TIMEOUT is exceeded.

Throws:
IOException

receive

protected void receive(char[] c,
                       int off,
                       int len)
                throws IOException
Receives data into an array of characters. This method will block until some input is available.

Throws:
IOException

receivedFirst

protected void receivedFirst()
Notifies all waiting threads that we have started to receive data


receivedLast

protected void receivedLast()
Notifies all waiting threads that the last character of data has been received.


read

public int read()
         throws IOException
Reads the next character of data from this piped stream. If no character is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown. If a thread was providing data characters to the connected piped writer, but the thread is no longer alive, then an IOException is thrown.

Overrides:
read in class Reader
Returns:
the next character of data, or -1 if the end of the stream is reached.
Throws:
IOException - if the pipe is broken.

read

public int read(char[] cbuf,
                int off,
                int len)
         throws IOException
Reads up to len characters of data from this piped stream into an array of characters. Less than len characters will be read if the end of the data stream is reached. This method blocks until at least one character of input is available. If a thread was providing data characters to the connected piped output, but the thread is no longer alive, then an IOException is thrown.

Specified by:
read in class Reader
Parameters:
cbuf - the buffer into which the data is read.
off - the start offset of the data.
len - the maximum number of characters read.
Returns:
the total number of characters read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
Throws:
IOException - if an I/O error occurs.

ready

public boolean ready()
              throws IOException
Tell whether this stream is ready to be read. A piped character stream is ready if the circular buffer is not empty.

Overrides:
ready in class Reader
Throws:
IOException - If an I/O error occurs

close

public void close()
           throws IOException
Closes this piped stream and releases any system resources associated with the stream.

Specified by:
close in interface Closeable
Specified by:
close in class Reader
Throws:
IOException - if an I/O error occurs.


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