FULL PRODUCT VERSION :
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Server VM (build 1.6.0_01-b06, mixed mode)

FULL OS VERSION :
WindowsXP (SP2+patches)
Linux 2.6.9-22.ELsmp x86_64
Linux 2.6.9-22.ELsmp i686 i386

A DESCRIPTION OF THE PROBLEM :
When using a java.nio.FloatBuffer in a loop, the values placed into the FloatBuffer via the put( float[], int, int) method are not always equal to the values of the source float[] data when the program is executed using the Hotspot Server VM (-server option).

Note that the problem appears to only be present when the jvm is executed with the -server option. If -client is used, the FloatBuffer values are correct.

Note that sometimes the data in the FloatBuffer is correct. It's the use of a FloatBuffer in a loop that appears to be part of the problem (at least as discovered and tested).

This problem appears to be new to Java 6 and is not present in the Java 1.4 or Java 5 vms that I tested.

THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: Did not try

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Yes

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a loop that executes more than 1 time
2. Copy an array for floats into a java.nio.FloatBuffer using the put(float[], int, int) method. Ref http://java.sun.com/javase/6/docs/api/java/nio/FloatBuffer.html#put(float[],%20int,%20int)
3. Compare values of the source float array to those values in the FloatBuffer
4. Execute with the '-server' jvm option (e.g. java -server FloatBufferTest)

EXPECTED VERSUS ACTUAL BEHAVIOR :
When tested in prior jvms and in the Java 6 jvm using the '-client' option, the source float array and the values copied into the FloatBuffer are the same (as they should be). When tested in the Java 6 jvm using the '-server' option, the source float array and the values copied into the FloatBuffer are not always the same when the FloatBuffer is being used inside of a loop.

ACTUAL -

java FloatBufferTest
0 loops experienced errors. Total FloatBuffer loops executed 1000
0 loops experienced errors. Total DoubleBuffer loops executed 1000
0 IntBuffer loops experienced errors. Total IntBuffer loops executed 1000
Java version 1.6.0_02-ea-b02
Java name Java HotSpot(TM) Client VM

java -server FloatBufferTest
Error count for the current loop in comparing FloatBuffer to float src array 17618
Error count for the current loop in comparing FloatBuffer to float src array 24386
2 loops experienced errors. Total FloatBuffer loops executed 1000
First FloatBuffer loop to error: 0
0 loops experienced errors. Total DoubleBuffer loops executed 1000
0 IntBuffer loops experienced errors. Total IntBuffer loops executed 1000
Java version 1.6.0_02-ea-b02
Java name Java HotSpot(TM) Server VM

REPRODUCIBILITY :
This bug can be reproduced always.



---------- BEGIN SOURCE ----------
import java.nio.ByteBuffer;
import java.nio.DoubleBuffer;
import java.nio.FloatBuffer;
import java.nio.IntBuffer;
import java.util.Random;

/**
 * The FloatBufferTest demonstrates an error in the FloatBuffer when executed
 * with the Java 6 jvm with the jvm arg '-server'. If the Java 6 jvm is executed
 * in client mode, then there is no error.
 *
 * Also worth noting is that the Java 1.4 and Java 5 jvms execute the code
 * without any errors for both jvm args '-server' and '-client'.
 *
 * To see the errors execute the code below using the Java 6 jvm with '-server'
 * specified.
 *
 * example: java -server FloatBufferTest
 *
 * Execute the same code using the same Java 6 jvm without the '-server' option
 * and no errors are produced.
 *
 * example: java FloatBufferTest or java -client FloatBufferTest
 *
 * Java version: Java version 1.6.0_01-b06
 *
 * Misc: The IntBuffer and DoubleBuffer are also tested in the same manner that
 * the FloatBuffer is tested and no errors have been seen using the same scenario.
 * Perhaps execution order of the methods may affect the outcome (not tested).
 */
public class FloatBufferTest {


private static int NUM_LOOPS = 1000;

//change to true to dump error values to console
//note that doing so may affect results
private static boolean DUMP_ERROR_VALUES = false;

public static void main(String[] args) {
long seed = 8675309;
int dlength = 50000; // 50000 entries

FloatBufferTest.testFloatBuffer(seed, dlength);
//test DoubleBuffer in the same manner
FloatBufferTest.testDoubleBuffer(seed, dlength);
//test IntBuffer in the same manner
FloatBufferTest.testIntBuffer(seed, dlength);

//dump some jvm info
String jvmversion = System.getProperty("java.vm.version");
String jvmname = System.getProperty("java.vm.name");
System.err.println("Java version " + jvmversion);
System.err.println("Java name " + jvmname);

}

/**
* Test the FloatBuffer
* @param pSeed the seed value
* @param pLength the number of data values
*/
protected static void testFloatBuffer(long pSeed, int pLength) {

int blength = 4; // 4 btyes
float[] floats = new float[pLength];

Random r = new Random(pSeed);
//populate src float array
for (int i = 0; i < pLength; i++) {
floats[i] = r.nextFloat();
}


int loopErrorCount = 0;
int firstLoopToErr = -1;





for (int ii = 0; ii <= NUM_LOOPS; ii++) {

ByteBuffer destbb = ByteBuffer.allocate(pLength * blength);
FloatBuffer fb = destbb.asFloatBuffer();
fb.put(floats, 0, pLength);

int errorCount = 0;
//compare source float values to those copied into the FloatBuffer
for (int i = 0; i < floats.length; i++) {
float fbfvalue = fb.get(i);
float srcvalue = floats[i];
//check for mismatching values
if (fbfvalue != srcvalue) {
errorCount++;

if (DUMP_ERROR_VALUES) {
System.err.println("*** Data values not equal error");
System.err.println(i + " (array index) Expected " + srcvalue
+ ", got " + fbfvalue);
}

}
} //end i

//check if there where any errors in loop execution
if (errorCount > 0) {
//track the first loop to error
if (firstLoopToErr == -1) {
firstLoopToErr = ii;
}
loopErrorCount++;
System.err
.println("Error count for the current loop in comparing FloatBuffer to float src array "
+ errorCount);
}


}// end ii

System.err.println(loopErrorCount + " loops experienced errors. Total FloatBuffer loops executed " + NUM_LOOPS);
if (loopErrorCount > 0) {
System.err.println("First FloatBuffer loop to error: " + firstLoopToErr);
}

}

/**
* Test the DoubleBuffer
* @param pSeed the seed value
* @param pLength the number of data values
*/
protected static void testDoubleBuffer(long pSeed, int pLength) {

int blength = 8; // 8 btyes
double[] src = new double[pLength];

Random r = new Random(pSeed);
//populate src array
for (int i = 0; i < pLength; i++) {
src[i] = r.nextDouble();
}


int loopErrorCount = 0;
int firstLoopToErr = -1;





for (int ii = 0; ii <= NUM_LOOPS; ii++) {

ByteBuffer destbb = ByteBuffer.allocate(pLength * blength);
DoubleBuffer fb = destbb.asDoubleBuffer();
fb.put(src, 0, pLength);

int errorCount = 0;
//compare source float values to those copied into the DoubleBuffer
for (int i = 0; i < src.length; i++) {
double fbfvalue = fb.get(i);
double srcvalue = src[i];
//check for mismatching values
if (fbfvalue != srcvalue) {
errorCount++;

if (DUMP_ERROR_VALUES) {
System.err.println("*** Data values not equal error");
System.err.println(i + " (array index) Expected " + srcvalue
+ ", got " + fbfvalue);
}

}
} //end i

//check if there where any errors in loop execution
if (errorCount > 0) {
//track the first loop to error
if (firstLoopToErr == -1) {
firstLoopToErr = ii;
}
loopErrorCount++;
System.err
.println("Error count for the current loop in comparing DoubleBuffer to double src array "
+ errorCount);
}


}// end ii

System.err.println(loopErrorCount + " loops experienced errors. Total DoubleBuffer loops executed " + NUM_LOOPS);
if (loopErrorCount > 0) {
System.err.println("First DoubleBuffer loop to error: " + firstLoopToErr);
}

}

/**
* Test the IntBuffer
* @param pSeed the seed value
* @param pLength the number of data values
*/
protected static void testIntBuffer(long pSeed, int pLength) {

int blength = 4; // 4 btyes
int[] src = new int[pLength];

Random r = new Random(pSeed);
//populate src array
for (int i = 0; i < pLength; i++) {
src[i] = r.nextInt();
}


int loopErrorCount = 0;
int firstLoopToErr = -1;





for (int ii = 0; ii <= NUM_LOOPS; ii++) {

ByteBuffer destbb = ByteBuffer.allocate(pLength * blength);
IntBuffer fb = destbb.asIntBuffer();
fb.put(src, 0, pLength);

int errorCount = 0;
//compare source float values to those copied into the IntBuffer
for (int i = 0; i < src.length; i++) {
int fbfvalue = fb.get(i);
int srcvalue = src[i];
//check for mismatching values
if (fbfvalue != srcvalue) {
errorCount++;

if (DUMP_ERROR_VALUES) {
System.err.println("*** Data values not equal error");
System.err.println(i + " (array index) Expected " + srcvalue
+ ", got " + fbfvalue);
}

}
} //end i

//check if there where any errors in loop execution
if (errorCount > 0) {
//track the first loop to error
if (firstLoopToErr == -1) {
firstLoopToErr = ii;
}
loopErrorCount++;
System.err
.println("Error count for the current loop in comparing IntBuffer to double src array "
+ errorCount);
}


}// end ii

System.err.println(loopErrorCount + " IntBuffer loops experienced errors. Total IntBuffer loops executed " + NUM_LOOPS);
if (loopErrorCount > 0) {
System.err.println("First IntBuffer loop to error: " + firstLoopToErr);
}

}


}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Preliminary testing shows the usage of put (int index, float value) (Ref http://java.sun.com/javase/6/docs/api/java/nio/FloatBuffer.html#put(int,%20float) )
to be a possible workaround, although it has not been tested on all platforms