RFR: 8319589: Attach from root to a user java process not supported in Mac [v2]

[Laurence Cable]

I believe that somewhere in the bowels of MacOS libc there is a 
(hopefully public) function that will map a UID to the UUID used to 
construct
the per-user directory path from a base 36(?) encoded string thereof, 
the leading 2 characters of which form the "buckets" in /var/folders
and the remainder of the encoded string forms the per user directory 
with the appropriate bucket...

if might make sense to perform a serious investigation to locate this 
function and then simply make a native call to map the target JVM euid
to the uuid and encode it, from which the actual /var/folders/... path 
can be constructed avoiding a costly traversal of the /var/folders
structure in the search for hsperfdata_user files?

Rgds

- Larry

On 6/18/25 9:40 AM, Sergey Chernyshev wrote:
> On Tue, 17 Jun 2025 04:51:58 GMT, David Holmes <dholmes at openjdk.org> wrote:
>
>>> Sergey Chernyshev has updated the pull request incrementally with two additional commits since the last revision:
>>>
>>>   - Update src/jdk.attach/macosx/classes/sun/tools/attach/VirtualMachineImpl.java
>>>     
>>>     Co-authored-by: Andrey Turbanov <turbanoff at gmail.com>
>>>   - addressed review comments
>> src/hotspot/os/posix/perfMemory_posix.cpp line 133:
>>
>>> 131: //
>>> 132:
>>> 133: #ifdef __APPLE__
>> This is a bit too much non-posix code in the posix file IMO. I'd rather see a `MACOS_ONLY` call later on to something defined in `os_bsd.cpp` for macOS.
> Thanks @dholmes-ora , I moved the function to `os_bsd.cpp`
>
> -------------
>
> PR Review Comment: https://git.openjdk.org/jdk/pull/25824#discussion_r2155061182