Class FifoBuffer

java.lang.Object

com.trilead.ssh2.channel.FifoBuffer

class FifoBuffer
extends Object

FIFO buffer for a reader thread and a writer thread to collaborate. Unlike a ring buffer, which uses a fixed memory regardless of the number of bytes currently in the buffer, this implementation uses a single linked list to reduce the memory footprint when the reader closely follows the writer, regardless of the capacity limit set in the constructor. In trilead, the writer puts the data we receive from the network, and the user code acts as a reader. A user code normally drains the buffer more quickly than what the network delivers, so this implementation saves memory while simultaneously allowing us to advertise a bigger window size for a large latency network.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
(package private) static final class	FifoBuffer.Page	Unit of buffer, singly linked and lazy created as needed.
(package private) class	FifoBuffer.Pointer	Points to a specific byte in a FifoBuffer.Page.

Field Summary

Fields

Modifier and Type	Field	Description
private boolean	closed	Set to true when the writer closes the write end.
private int	limit	Cap to the # of bytes that we can hold.
private final Object	lock
private final int	pageSize
private FifoBuffer.Pointer	r	The position at which the next read/write will happen.
private int	sz	Number of bytes currently in this ring buffer
private FifoBuffer.Pointer	w	The position at which the next read/write will happen.

Constructor Summary

Constructors

Constructor	Description
FifoBuffer(int pageSize, int limit)
FifoBuffer(Object lock, int pageSize, int limit)

Method Summary

Modifier and Type	Method	Description
void	close()
private FifoBuffer.Page	newPage()
int	read(byte[] buf, int start, int len)
(package private) int	readable()	Number of bytes readable
private void	releaseRing()	If the ring is no longer needed, release the buffer.
void	setLimit(int newLimit)
(package private) int	writable()	Number of bytes writable
void	write(byte[] buf, int start, int len)
int	writeTo(OutputStream out)	Write whatever readable to the specified OutputStream, then return.

Methods inherited from class Object

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

Field Details

lock

private final Object lock

sz

private int sz

Number of bytes currently in this ring buffer

limit

private int limit

Cap to the # of bytes that we can hold.

pageSize

private final int pageSize

r

private FifoBuffer.Pointer r

The position at which the next read/write will happen.

w

private FifoBuffer.Pointer w

The position at which the next read/write will happen.

closed

private boolean closed

Set to true when the writer closes the write end.

Constructor Details

FifoBuffer

FifoBuffer(int pageSize,
 int limit)

FifoBuffer

FifoBuffer(Object lock,
 int pageSize,
 int limit)

Method Details

setLimit

public void setLimit(int newLimit)

newPage

private FifoBuffer.Page newPage()

readable

int readable()

Number of bytes readable

writable

int writable()

Number of bytes writable

write

public void write(byte[] buf,
 int start,
 int len)
           throws InterruptedException

Throws:

InterruptedException

close

public void close()

releaseRing

private void releaseRing()

If the ring is no longer needed, release the buffer.

read

public int read(byte[] buf,
 int start,
 int len)
         throws InterruptedException

Throws:

InterruptedException

See Also:

• InputStream.read(byte[],int,int)

writeTo

public int writeTo(OutputStream out)
            throws IOException

Write whatever readable to the specified OutputStream, then return.

Throws:

IOException