RFR (S) 8059677: Thread.getName() instantiates Strings

[Aleksey Shipilev]

Hi Staffan,

Ow, it seems very like it.
So, what testlist have I missed to catch this?

-Aleksey.

On 11/10/2014 05:51 PM, Staffan Larsen wrote:
> I’m afraid this change requires changes in the Serviceability Agent as well. See OopUtilities.threadOopGetName() for example.
> 
> /Staffan
> 
>> On 10 nov 2014, at 15:19, Aleksey Shipilev <aleksey.shipilev at oracle.com> wrote:
>>
>> Hi David, Chris,
>>
>> On 11/10/2014 04:53 PM, Chris Hegarty wrote:
>>> On 10/11/14 12:56, David Holmes wrote:
>>>> On 10/11/2014 9:52 PM, Chris Hegarty wrote:
>>>>> I have only looked at the libraries changes, and I think they make sense
>>>>> . As in, I can find no reason why the name cannot be changed to be a
>>>>> String.
>>>>
>>>> Very quick response, but IIRC this has been examined in the past and
>>>> there were reasons why it can't/shouldn't be done. Will try to dig out
>>>> more details in the morning.
>>>
>>> If there was previous discussion on this, that revealed some substantial
>>> issue, that would be great, but I can't recall, or find, it now.
>>>
>>> Hotspot express, and the desire for hotspot to run with different
>>> library versions, would certainly cause complication, but I don't
>>> believe that is an issue now.
>>>
>>> Just on that, the library changes are minimal, and if this were to
>>> proceed then they can accompany the hotspot change, as they make their
>>> way into jdk9/dev.
>>>
>>> Anyway, this should await your reply.
>>
>> Alan was having the same concern, there is an issue with JNI/JVMTI and
>> other power users that might break when exposed to under-constructed
>> Thread, e.g:
>> https://bugs.openjdk.java.net/browse/JDK-6412693
>>
>> This is why I ran jvmti and serviceability tests for this change,
>> yielding no failures. This reinforces my belief this patch does not
>> break the important invariant: if there is a problem with "Thread.name =
>> name.toCharArray()" anywhere in Thread code, then "Thread.name = name"
>> does neither regress it further nor fixes it.
>>
>> Then I speculated that having char[] name would help VM initialize the
>> name if we wanted to switch to complete VM-side initialization of
>> Thread, but it seems we can do String oop instantiation in the similar vein.
>>
>> Caching the name feels like a band-aid, that will probably complicate
>> the Thread initialization on VM side even more. Let's wait and see if
>> David can come up with some horror issue we are overlooking. :)
>>
>> Thanks,
>> -Aleksey.
>>
>