RFR(S) 8206183: Possible construct EMPTY_STACK and allocation stack, etc. on first use

[Zhengyu Gu]

Hi David,

On 07/09/2018 12:37 AM, David Holmes wrote:
> Hi Zhengyu,
> 
> On 7/07/2018 9:36 PM, Zhengyu Gu wrote:
>> Hi,
>>
>> NMT has to workaround static initialization order issues: some of 
>> static objects, who allocate memory inside their constructors, may be 
>> initialized ahead of NMT, so NMT is forced to initialize itself early 
>> and risks its static objects may be reinitialized by C runtime.
>>
>> The workaround was to declare storage for the static objects as 
>> primitive arrays, then use placement new operator to initialize them, 
>> or just initialize them eagerly, if the results are constants.
>>
>> But the solution is not elegant, could break with some compilers.
>> A better solution is to use "construct on First Use Idiom" pattern 
>> (https://isocpp.org/wiki/faq/ctors#static-init-order), cause we only 
>> have initialization order problems, those static objects do not have 
>> dependencies on other static objects, so we don't suffer from static 
>> deinitialization problems.
> 
> Okay but this relies on C+11 thread-safe static initialization. That's 
> only available in VS2015 and above (which should be okay for JDK 12+). 
> What about other compilers? Does it have to be enabled via any 
> compilation flags?

Thanks for pointing out.

NMT is always initialized while JVM is still in single-thread mode, so I 
think it is safe even without language support, or I miss something here?

-Zhengyu


> 
> I'm currently running this through some additional internal build/tests.
> 
> Thanks,
> David
> -----
> 
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8206183
>> Webrev: http://cr.openjdk.java.net/~zgu/8206183/webrev.00/
>>
>> Test:
>>
>>    hotspot_nmt on Linux 64 (fastdebug and release)
>>    Submit-test.
>>
>>
>> Thanks,
>>
>> -Zhengyu