Request for review:8020309:Remove InstanceKlass::_cached_class_file_len and record the length together with the cached class file bytes

[Ioi Lam]

Hi Jiangli,

I think it's better to move the logic of deciding the length into JVMTI. 
E.g., have something like

struct JvmtiCachedClassFileData {
    int _length;
    unsigned char data[1];
};

void 
instanceKlass::set_jvmti_cached_class_file_data(JvmtiCachedClassFileData 
*data);

- Ioi

On 07/10/2013 04:58 PM, Jiangli Zhou wrote:
> Hi,
>
> Please review the webrev for JDK-8020309 
> <https://jbs.oracle.com/bugs/browse/JDK-8020309>:
>
> http://cr.openjdk.java.net/~jiangli/8020309/webrev.00/
>
> The _cached_class_file_bytes and _cached_class_file_len are not 
> set/used if no jvmti agent is attached. The _cached_class_file_len 
> field can be eliminated and the file length can be recorded as part of 
> the cached class data in _cached_class_file_bytes for redefined class. 
> The above change allocates extra 4bytes when allocating memory for 
> cached class file and stores the length as the first 4bytes and the 
> file data as the rest. It saves 4 bytes per class. For classes 
> redefined, the memory usage is the same.
>
> Tested with following tests and JPRT:
>
>     jdk/test/java/lang/instrument
>     jdk/test/com/sun/jdi
>     nsk.jvmti
>     nsk.jdi
>     nsk.hprof
>
> Thanks,
> Jiangli

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