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package sun.rmi.transport.tcp;

import java.io.*;

MultiplexInputStream manages receiving data over a connection managed
by a ConnectionMultiplexer object.  This object is responsible for
requesting more bytes of data as space in its internal buffer becomes
available.
Author:
Peter Jones/**
 * MultiplexInputStream manages receiving data over a connection managed
 * by a ConnectionMultiplexer object.  This object is responsible for
 * requesting more bytes of data as space in its internal buffer becomes
 * available.
 *
 * @author Peter Jones
 */
final class MultiplexInputStream extends InputStream {

    
object managing multiplexed connection /** object managing multiplexed connection */
    private ConnectionMultiplexer manager;

    
information about the connection this is the input stream for /** information about the connection this is the input stream for */
    private MultiplexConnectionInfo info;

    
input buffer /** input buffer */
    private byte buffer[];

    
number of real data bytes present in buffer /** number of real data bytes present in buffer */
    private int present = 0;

    
current position to read from in input buffer /** current position to read from in input buffer */
    private int pos = 0;

    
pending number of bytes this stream has requested /** pending number of bytes this stream has requested */
    private int requested = 0;

    
true if this connection has been disconnected /** true if this connection has been disconnected */
    private boolean disconnected = false;

    
lock acquired to access shared variables:
buffer, present, pos, requested, & disconnected
WARNING:  Any of the methods manager.send*() should not be
invoked while this lock is held, since they could potentially
block if the underlying connection's transport buffers are
full, and the manager may need to acquire this lock to process
and consume data coming over the underlying connection.
/**
     * lock acquired to access shared variables:
     * buffer, present, pos, requested, & disconnected
     * WARNING:  Any of the methods manager.send*() should not be
     * invoked while this lock is held, since they could potentially
     * block if the underlying connection's transport buffers are
     * full, and the manager may need to acquire this lock to process
     * and consume data coming over the underlying connection.
     */
    private Object lock = new Object();

    
level at which more data is requested when read past /** level at which more data is requested when read past */
    private int waterMark;

    
data structure for holding reads of one byte /** data structure for holding reads of one byte */
    private byte temp[] = new byte[1];

    
Create a new MultiplexInputStream for the given manager.
Params:
manager – object that manages this connection
info – structure for connection this stream reads from
bufferLength – length of input buffer/**
     * Create a new MultiplexInputStream for the given manager.
     * @param manager object that manages this connection
     * @param info structure for connection this stream reads from
     * @param bufferLength length of input buffer
     */
    MultiplexInputStream(
        ConnectionMultiplexer    manager,
        MultiplexConnectionInfo  info,
        int                      bufferLength)
    {
        this.manager = manager;
        this.info    = info;

        buffer = new byte[bufferLength];
        waterMark = bufferLength / 2;
    }

    
Read a byte from the connection.
/**
     * Read a byte from the connection.
     */
    public synchronized int read() throws IOException
    {
        int n = read(temp, 0, 1);
        if (n != 1)
            return -1;
        return temp[0] & 0xFF;
    }

    
Read a subarray of bytes from connection.  This method blocks for
at least one byte, and it returns the number of bytes actually read,
or -1 if the end of the stream was detected.
Params:
b – array to read bytes into
off – offset of beginning of bytes to read into
len – number of bytes to read/**
     * Read a subarray of bytes from connection.  This method blocks for
     * at least one byte, and it returns the number of bytes actually read,
     * or -1 if the end of the stream was detected.
     * @param b array to read bytes into
     * @param off offset of beginning of bytes to read into
     * @param len number of bytes to read
     */
    public synchronized int read(byte b[], int off, int len) throws IOException
    {
        if (len <= 0)
            return 0;

        int moreSpace;
        synchronized (lock) {
            if (pos >= present)
                pos = present = 0;
            else if (pos >= waterMark) {
                System.arraycopy(buffer, pos, buffer, 0, present - pos);
                present -= pos;
                pos = 0;
            }
            int freeSpace = buffer.length - present;
            moreSpace = Math.max(freeSpace - requested, 0);
        }
        if (moreSpace > 0)
            manager.sendRequest(info, moreSpace);
        synchronized (lock) {
            requested += moreSpace;
            while ((pos >= present) && !disconnected) {
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                }
            }
            if (disconnected && pos >= present)
                return -1;

            int available = present - pos;
            if (len < available) {
                System.arraycopy(buffer, pos, b, off, len);
                pos += len;
                return len;
            }
            else {
                System.arraycopy(buffer, pos, b, off, available);
                pos = present = 0;
                // could send another request here, if len > available??
                return available;
            }
        }
    }

    
Return the number of bytes immediately available for reading.
/**
     * Return the number of bytes immediately available for reading.
     */
    public int available() throws IOException
    {
        synchronized (lock) {
            return present - pos;
        }
    }

    
Close this connection.
/**
     * Close this connection.
     */
    public void close() throws IOException
    {
        manager.sendClose(info);
    }

    
Receive bytes transmitted from connection at remote endpoint.
Params:
length – number of bytes transmitted
in – input stream with those bytes ready to be read/**
     * Receive bytes transmitted from connection at remote endpoint.
     * @param length number of bytes transmitted
     * @param in input stream with those bytes ready to be read
     */
    void receive(int length, DataInputStream in)
        throws IOException
    {
        /* TO DO: Optimize so that data received from stream can be loaded
         * directly into user's buffer if there is a pending read().
         */
        synchronized (lock) {
            if ((pos > 0) && ((buffer.length - present) < length)) {
                System.arraycopy(buffer, pos, buffer, 0, present - pos);
                present -= pos;
                pos = 0;
            }
            if ((buffer.length - present) < length)
                throw new IOException("Receive buffer overflow");
            in.readFully(buffer, present, length);
            present += length;
            requested -= length;
            lock.notifyAll();
        }
    }

    
Disconnect this stream from all connection activity.
/**
     * Disconnect this stream from all connection activity.
     */
    void disconnect()
    {
        synchronized (lock) {
            disconnected = true;
            lock.notifyAll();
        }
    }
}