Developer CD Series 2000 November: Tool Chest/Dev.CD Nov 00 TC Disk 1.toast/Sample Code/Java/JavaRadioStation/Source/com/apple/jens/radio/DJ.java

Java Source | 2000-09-28 | 6.4 KB | 191 lines | [TEXT/CWIE]

/*
    File:        DJ.java

    Copyright:     © Copyright 1999-2000 Apple Computer, Inc. All rights reserved.

    Disclaimer:    IMPORTANT:  This Apple software is supplied to you by Apple Computer, Inc.
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    Change History (most recent first):

*/


package com.apple.jens.radio;

import java.io.*;


/** An abstract base class that generates MP3-format Buffers to be streamed by Transmitters.
    A DJ subclass might get the data from local MP3 files (like FileDJ)
    or by relaying a stream from a remote MP3 server.
    @see FileDJ
*/

public abstract class DJ extends Thread {

    /** Creates a DJ thread but doesn't start it yet. */
    public DJ( ) {
        super("DJ");
    }


    /** Sets the DJ's Station -- this is done once, when the DJ is created. */
    public void setStation( Station station ) {
        fStation = station;
        setName(station.getName()+"'s DJ");

        int bufferCount = station.getProperties().getIntProperty(kPropBufferCount,kDefaultBufferCount);
        fBuffers = new Buffer[bufferCount];
        // The array elements start out null since no buffers have been read yet.
    }


    public Station getStation( ) {
        return fStation;
    }


    // BUFFER ACCESS:


    //FIX: A better design for this would be to implement a BufferIterator,
    // to spare clients from having to deal with numeric indices.


    /** Returns the buffer index for a Transmitter to start with */
    int getFirstBufferIndex( ) {
        // Start 'em halfway around the ring to minimize chances of collision:
        return (fCurBuf + fBuffers.length/2) % fBuffers.length;
    }


    /** Returns the nth buffer counting around the buffer ring
        (using modulo arithmetic to index into the ring array.)
        This method is for use by Transmitters (readers), <i>not</i> by
        DJ subclasses. It will block if the nth buffer is currently
        being written to by the DJ, thus preventing Transmitters from
        overtaking the DJ. */
    Buffer getFilledBuffer( int n ) throws InterruptedException {
        if( n < 0 ) throw new IllegalArgumentException(Integer.toString(n));
        n = n % fBuffers.length;

        synchronized(this) {
            // Block until the buffer's been created and is no longer in use by the DJ:
            while( n == fCurBuf || fBuffers[n]==null )
                this.wait();        // Wait for getNextFreeBuffer to notify
        }

        return fBuffers[n];
    }


    /** Returns the next available buffer for the DJ to write to.
        This method should be called only by the subclass's <code>spin</code> method. */
    protected Buffer getNextFreeBuffer( ) {
        synchronized(this) {
            ++fCurBuf;
            if( fCurBuf == fBuffers.length )
                fCurBuf = 0;
            this.notifyAll();    // wake up Transmitters blocked in getBuffer method
        }

        Buffer next = fBuffers[fCurBuf];
        if( next == null )        // Allocate buffers 1st time around
            next = fBuffers[fCurBuf] = new Buffer(fStation.getStationName()+"#"+fCurBuf);
        return next;
    }


    // RUN-LOOP:


    /** Should be overridden by the caller to spin some tunes and generate
        some Buffers via setCurrentBuffer. */
    protected abstract void spin( ) throws IOException, InterruptedException;


    /** The DJ thread's run loop.
        Don't call this directly -- the DJ's owner should call start instead.
        @see Station */
    public void run( ) {
        try{
            while(true) {
                spin();
            }
        }catch( IOException x ) {
            Radio.WARN(1,this,"Caught a fatal IOException, exiting...");
            x.printStackTrace(System.err);
        }catch( InterruptedException ix ) {
            LOG(1,"Interrupted! Exiting...");
        }
        //FIX: When this thread exits, all Transmitters must be shut down
        //        or they will block forever...
    }


    protected void LOG( int level, String msg ) {
        Radio.LOG(level,getName(),msg);
    }


    // INSTANCE DATA:


    private Station fStation;

    /** The circular ring of buffers used by the DJ and Transmitters. */
    private Buffer[] fBuffers;

    /** The index into fBuffers of the buffer the DJ is currently writing to.
        The buffer with this index will never be handed out
        to Transmitters -- they'll block until fCurBuf is incremented. */
    private int fCurBuf = -1;


    // STATIC DATA:


    /** The default number of buffers, if not overridden in Defaults or station prop files. */
    public static final int kDefaultBufferCount = 6;


    // PROPERTIES:


    public static final String kPropBufferCount = "buffer-count";

}