Thread safety problem with java.util.zip.Deflator's input array

FULL PRODUCT VERSION :
java version "1.8.0_91"
Java(TM) SE Runtime Environment (build 1.8.0_91-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.91-b14, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Darwin C02NH1CUG3QT.local 15.5.0 Darwin Kernel Version 15.5.0: Tue Apr 19 18:36:36 PDT 2016; root:xnu-3248.50.21~8/RELEASE_X86_64 x86_64


A DESCRIPTION OF THE PROBLEM :
Starting with 8u40, if you turn on -Xcheck:jni it will always make a copy of the array when GetPrimitiveArrayCritical/ReleasePrimitiveArrayCritical is using. The native code for Deflater uses that on the input array. If you are using the array as a ring buffer and compressing one chunk while writing to another, you can "lose" writes when it copies the original array back in.

I think the bug is in the Deflater logic, the change to -Xcheck:jni is per spec as they mentioned when they added it: https://bugs.openjdk.java.net/browse/JDK-6311046 .



REGRESSION. Last worked in version 7u80

ADDITIONAL REGRESSION INFORMATION:
I went by the comment in https://bugs.openjdk.java.net/browse/JDK-6311046, I didn't check against 1.7.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the test case code submitted below.

Run like this:
---
$ java -cp . -Xcheck:jni -Xms64m -Xmx512m DeflateGate
---

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The program should run until manually killed, reporting progress.
ACTUAL -
You get runs like this:

---
$ java -cp . -Xcheck:jni -Xms64m -Xmx512m DeflateGate
WARNING in native method: JNI call made without checking exceptions when required to from CallStaticObjectMethod
WARNING in native method: JNI call made without checking exceptions when required to from CallObjectMethod
DEFLATE:: bytesDeflated: 1048902, fill val: 5
FAIL: filler: -120, backer[x]: -76, x: 0
DEFLATE:: bytesDeflated: 1048902, fill val: -76
$ java -cp . -Xcheck:jni -Xms64m -Xmx512m DeflateGate
WARNING in native method: JNI call made without checking exceptions when required to from CallStaticObjectMethod
WARNING in native method: JNI call made without checking exceptions when required to from CallObjectMethod
FAIL: filler: -1, backer[x]: 50, x: 0
DEFLATE:: bytesDeflated: 1048902, fill val: 50
$ java -cp . -Xcheck:jni -Xms64m -Xmx512m DeflateGate
WARNING in native method: JNI call made without checking exceptions when required to from CallStaticObjectMethod
WARNING in native method: JNI call made without checking exceptions when required to from CallObjectMethod
DEFLATE:: bytesDeflated: 1048902, fill val: -102
DEFLATE:: bytesDeflated: 1048902, fill val: -72
DEFLATE:: bytesDeflated: 1048902, fill val: 117
FAIL: filler: -48, backer[x]: 9, x: 0
DEFLATE:: bytesDeflated: 1048902, fill val: 9
---

REPRODUCIBILITY :
This bug can be reproduced often.

---------- BEGIN SOURCE ----------
import java.util.Arrays;
import java.util.Random;
import java.util.zip.Deflater;

// I get this to fail every time using 1.8.0_51 and 91 from the command like using:
// $ java -cp . -Xcheck:jni -Xms64m -Xmx512m DeflateGate


public class DeflateGate {

public static void main(String[] args) {
int bufSize = 2 * 1024 * 1024;;
byte[] backer = new byte[bufSize];

new Random().nextBytes(backer);

Thread t = new Thread() {
public void run() {
byte[] dumpster;
Deflater deflater = new Deflater();
while (true) {
dumpster = new byte[2 * bufSize];
deflater.reset();
deflater.setInput(backer, bufSize/2, bufSize/2);
deflater.finish();
int bytesDeflated = deflater.deflate(dumpster);
System.out.println("DEFLATE:: bytesDeflated: " + bytesDeflated + ", fill val: " + backer[0]);
}
}
};
t.start();

byte filler = 1;
long count = 1;
while (true) {
//Arrays.fill(backer, filler);
backer[0] = filler;
//System.gc();

// I started out doing the whole array and then wanted to speed it up.
// If you remove this one iteration loop, it won't fail. I don't know why.
for (int x=0; x < 1; x++) {
if (backer[x] != filler) {
System.out.println("FAIL: filler: " + filler + ", backer[x]: " + backer[x] + ", x: " + x);
System.exit(-1);
}
}
if (count % 10000000 == 0) {
System.out.println("MAIN:: Done with count: " + count);
}
filler++;
count++;
}

}

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

CUSTOMER SUBMITTED WORKAROUND :
If you synchronize on the array around the array write and the Deflater.delate() call it won't fail.

If you remove the -Xcheck:jni flag, it won't fail.