The following program demonstrates that accessing elements of a byte buffer is
significantly slower with C1 than accessing elements of an array:

    % /usr/local/java/jdk1.4/linux-i386/bin/java -client -showversion BBSpeed
    java version "1.4.0-beta"
    Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta-b50)
    Java HotSpot(TM) Client VM (build 1.4beta-B50, mixed mode)

    array 225
    array rev 286
    heap 1147
    heap rev 1148
    direct 3301
    direct rev 3304
    % 

I get similar numbers on Solaris (times are in ms).

(The numbers for direct byte buffers are even worse than those for
 heap-allocated byte buffers due to the fact that C1 does not yet inline
 sun.misc.Unsafe operations (4411596).)

Making both heap and direct buffers perform as well as arrays (or nearly so) is
critical to the performance of the java.nio subsystem.

-- mr@eng 2001/2/4


---- BBSpeed.java

import java.nio.*;


public class BBSpeed {

    static final int SIZE = 4096;
    static final int TRIALS = 4096;

    static int sum(ByteBuffer bb) {
	int n = bb.capacity();
	int a = 0;
	bb.rewind();
	for (int j = 0; j < n; j++)
	    a += bb.get(j);
	return a;
    }

    static int sumReverse(ByteBuffer bb) {
	int n = bb.capacity();
	int a = 0;
	bb.rewind();
	for (int j = n - 1; j >= 0; j--)
	    a += bb.get(j);
	return a;
    }

    static int time(String name, ByteBuffer bb) {
	int n = bb.capacity();
	bb.limit(bb.capacity());
	int a = 0;

	for (int i = 0; i < TRIALS; i++) sum(bb);
	long start = System.currentTimeMillis();
	for (int i = 0; i < TRIALS; i++) sum(bb);
	System.out.println(name + " " + (System.currentTimeMillis() - start));

	for (int i = 0; i < TRIALS; i++) sumReverse(bb);
	start = System.currentTimeMillis();
	for (int i = 0; i < TRIALS; i++) sumReverse(bb);
	System.out.println(name + " rev " + (System.currentTimeMillis() - start));

	return a;
    }

    static int sum(byte[] ba) {
	int n = ba.length;
	int a = 0;
	for (int j = 0; j < n; j++)
	    a += ba[j];
	return a;
    }

    static int sumReverse(byte[] ba) {
	int n = ba.length;
	int a = 0;
	for (int j = n - 1; j >= 0; j--)
	    a += ba[j];
	return a;
    }

    static int timeArray() {
	byte[] ba = new byte[SIZE];
	int a = 0;
	
	for (int i = 0; i < TRIALS; i++) a += sum(ba);
	long start = System.currentTimeMillis();
	for (int i = 0; i < TRIALS; i++) a += sum(ba);
	System.out.println("array " + (System.currentTimeMillis() - start));

	for (int i = 0; i < TRIALS; i++) a += sumReverse(ba);
	start = System.currentTimeMillis();
	for (int i = 0; i < TRIALS; i++) a += sumReverse(ba);
	System.out.println("array rev " + (System.currentTimeMillis() - start));

	return a;
    }

    public static void main(String[] args) {
	String key = "hda";
	if (args.length == 1)
	    key = args[0];
	int a = 0;
	if (key.indexOf('a') >= 0)
	    a += timeArray();
	if (key.indexOf('h') >= 0)
	    a += time("heap", ByteBuffer.allocate(SIZE));
	if (key.indexOf('d') >= 0)
	    a += time("direct", ByteBuffer.allocateDirect(SIZE));
	System.exit(a);
    }

}