Question about MarkOop

[Andrew Haley]

On 26/12/14 17:36, Viacheslav Kovalevskyi wrote:

> 
> In first case (before synchronization), real life:
>  OFFSET  SIZE  TYPE DESCRIPTION                    VALUE
>       0     4       (object header)                0d 00 00 00 (0000 1101 0000 0000 0000 0000 0000 0000)
>       4     4       (object header)                00 00 00 00 (0000 0000 0000 0000 0000 0000 0000 0000)
> …
> according to dict this is: 
>         //  unused:25 hash:31 -->| unused:1   age:4    biased_lock:1 lock:2 (normal object)
> 
> question: why we have this strange first byte (0000 1101)? According to layout doc it should be unused

No it shouldn't: it says "age:4    biased_lock:1 lock:2" for the least-
significant bits.

> Second case is even funnier, real life:
>  OFFSET  SIZE  TYPE DESCRIPTION                    VALUE
>       0     4       (object header)                0d 70 00 1a (0000 1101 0111 0000 0000 0000 0001 1010)
>       4     4       (object header)                9b 7f 00 00 (1001 1011 0111 1111 0000 0000 0000 0000)
> …
> according to dict this is: 
>         //  JavaThread*:54 epoch:2 unused:1   age:4    biased_lock:1 lock:2 (biased object)
> 
> question: why first byte remains the same, looks like Thread pointer was written to the different offset then it should (according to the doc).
> Also the first byte remains the same.

The status bits are the same.

Andrew.