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

David Holmes david.holmes at oracle.com
Wed Nov 12 04:48:53 UTC 2014

On 12/11/2014 12:40 AM, Aleksey Shipilev wrote:
> Hi,
> On 11/09/2014 09:45 PM, Aleksey Shipilev wrote:
>> Thread.getName() returns String, and does new String instantiation every
>> time, because the thread name is stored in char[]. Even though we use a
>> private String constructor that shares the char[] array without copying
>> it, this still hurts some use cases (think extra-fast logging). To the
>> extent some people actually maintain Map<Thread, String> to avoid it.
>>   https://bugs.openjdk.java.net/browse/JDK-8059677
>> Here's the attempt to maintain String instead of char[]:
>>   http://cr.openjdk.java.net/~shade/8059677/webrev.01.jdk/
>>   http://cr.openjdk.java.net/~shade/8059677/webrev.01.hs/
> Updated webrevs:
>    http://cr.openjdk.java.net/~shade/8059677/webrev.02.jdk/
>    http://cr.openjdk.java.net/~shade/8059677/webrev.02.hs/
> This version incorporates feedbacks from Chris, Staffan and David. I
> think it is very close to what we would like to push. Opinions?

All looks good to me.

But I also noticed this strange (to me) assertion in javaClasses.cpp

  void java_lang_Thread::set_name(oop java_thread, oop name) {
     assert(java_thread->obj_field(_name_offset) == NULL, "name should 
be NULL");
     java_thread->obj_field_put(_name_offset, name);

and on investigation it seems like this is dead code - I couldn't locate 
a call to java_lang_Thread::set_name ?? It would only be usable on an 
attaching thread (else name can't be null) and we pass the name to the 
Thread constructor in that case.


> Testing: JPRT, jdk/test/java/lang/Thread jtreg, hotspot/test/runtime/
> jtreg, vm.quick.testlist, nsk.jvmti.testlist, svc.quick.testlist,
> vm.tmtools.testlist
> Thanks,
> -Aleksey.

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