Array accesses using sun.misc.Unsafe cause data corruption or SIGSEGV

[Mehmet Dogan]

Btw, (thanks to one my colleagues), when address calculation in the loop is
converted to

long address = baseAddress + (i * 8)

test passes. Only difference is next long pointer is calculated using
integer 8 instead of long 8.

```
for (int i = 0; i < count; i++) {
    long address = baseAddress + (i * 8); // <--- here, integer 8 instead
of long 8

    long expected = i;
    unsafe.putLong(address, expected);

    long actual = unsafe.getLong(address);

    if (expected != actual) {
        throw new AssertionError("Expected: " + expected + ", Actual: " +
actual);
    }
}
```

On Tue, Jun 9, 2015 at 1:07 PM Mehmet Dogan <mehmet at hazelcast.com> wrote:

> Hi all,
>
> While I was testing my app using java 8, I encountered the previously
> reported sun.misc.Unsafe issue.
>
> https://bugs.openjdk.java.net/browse/JDK-8076445
>
> http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2015-April/017685.html
>
> Issue status says it's resolved with resolution "Cannot Reproduce".  But
> unfortunately it's still reproducible using "1.8.0_60-ea-b18" and
> "1.9.0-ea-b67".
>
> Test is very simple:
>
> ```
> public static void main(String[] args) throws Exception {
>         Unsafe unsafe = findUnsafe();
>         // 10000 pass
>         // 100000 jvm crash
>         // 1000000 fail
>         int count = 100000;
>         long size = count * 8L;
>         long baseAddress = unsafe.allocateMemory(size);
>
>         try {
>             for (int i = 0; i < count; i++) {
>                 long address = baseAddress + (i * 8L);
>
>                 long expected = i;
>                 unsafe.putLong(address, expected);
>
>                 long actual = unsafe.getLong(address);
>
>                 if (expected != actual) {
>                     throw new AssertionError("Expected: " + expected + ",
> Actual: " + actual);
>                 }
>             }
>         } finally {
>             unsafe.freeMemory(baseAddress);
>         }
>     }
> ```
> It's not failing up to version 1.8.0.31, by starting 1.8.0.40 test is
> failing constantly.
>
> - With iteration count 10000, test is passing.
> - With iteration count 100000, jvm is crashing with SIGSEGV.
> - With iteration count 1000000, test is failing with AssertionError.
>
> When one of compilation (-Xint) or inlining (-XX:-Inline) or
> on-stack-replacement (-XX:-UseOnStackReplacement) is disabled, test is not
> failing at all.
>
> I tested on platforms:
> - Centos-7/openjdk-1.8.0.45
> - OSX/oraclejdk-1.8.0.40
> - OSX/oraclejdk-1.8.0.45
> - OSX/oraclejdk-1.8.0_60-ea-b18
> - OSX/oraclejdk-1.9.0-ea-b67
>
> Previous issue comment (
> https://bugs.openjdk.java.net/browse/JDK-8076445?focusedCommentId=13633043#comment-13633043)
> says "Cannot reproduce based on the latest version". I hope that latest
> version is not mentioning to '1.8.0_60-ea-b18' or '1.9.0-ea-b67'. Because
> both are failing.
>
> I'm looking forward to hearing from you.
>
> Thanks,
> -Mehmet Dogan-
> --
>
> @mmdogan
>
-- 

@mmdogan
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