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

[Staffan Larsen]

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.
>