Need help to understand TLS behavior

[David Holmes]

On 15/12/2015 6:53 AM, Martin Buchholz wrote:
> Thread local storage is trouble.
>
> java stack sizes should be in _addition_ to any OS overhead, which includes TLS.

TLS shouldn't be coming out the stack of the thread AFAIK - I see 
nothing about that in "ELF Handling for Thread Local Storage". That is 
why I want to know more about the test, the compilation environment and 
the execution environment.

> IOW, the java thread stack size should actually be available for stack frames.
> Hotspot should be fixed, but it's not easy.

Do you mean that the value specified at the Java level should be rounded 
up to accommodate guard pages etc at the native level?

David
-----

> On Mon, Dec 14, 2015 at 12:47 PM, David Holmes <david.holmes at oracle.com> wrote:
>> On 14/12/2015 11:06 PM, cheleswer sahu wrote:
>>>
>>> Hi David,
>>> TLS is thread local storage. In test program it is defined using
>>>
>>> #define TLS_SIZE 32
>>> int __thread  XYZ[TLS_SIZE * 1024];
>>
>>
>> Thanks for clarifying. What test is that? I'm guessing this may be a linux
>> only test? Which platform do you see the problem on?
>>
>> We don't unconditionally use compiler-based TLS as some platforms may not
>> support it.
>>
>> That aside that declaration should really be static I think.
>>
>> David
>> -----
>>
>>
>>> Regards,
>>> Cheleswer
>>> On 12/14/2015 6:29 PM, David Holmes wrote:
>>>>
>>>> What is TLS in this context?
>>>>
>>>> Thanks,
>>>> David
>>>>
>>>> On 14/12/2015 10:34 PM, cheleswer sahu wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> I am investigating an issue, in which test with TLS size set to 32K is
>>>>> failing with StackOverFlowError. During investigation I found the below
>>>>> code
>>>>>
>>>>> http://hg.openjdk.java.net/jdk8u/jdk8u/jdk/file/tip/src/solaris/classes/java/lang/UNIXProcess.java
>>>>>
>>>>>
>>>>>
>>>>>    ThreadFactory threadFactory = grimReaper -> {
>>>>>                   // Our thread stack requirement is quite modest.
>>>>>                   Thread t = new Thread(systemThreadGroup, grimReaper,
>>>>>                                         "process reaper", 32768);
>>>>>
>>>>> Here reaper thread is created with fixed stack size "32768 ", which
>>>>> causes StackOverFlowError  when TLS is set to 32k around.
>>>>> If I remove this fixed size and make it default, test works fine.
>>>>>
>>>>> Thread t = new Thread(systemThreadGroup, grimReaper,
>>>>>                                         "process reaper");
>>>>>
>>>>> I have run several test with TLS size 32k , 64k ,128k and more .
>>>>> The interesting part, it works well with 64k and 128k TLS size but not
>>>>> with 32k.
>>>>> So my questions are as follows:
>>>>>>
>>>>>> What is the motivation behind the fixed thread stack size ?
>>>>>> will it be ok to replace the fixed stack size with default or stack
>>>>>
>>>>> size setting is platform sensitive?
>>>>>>
>>>>>> How TLS sizes are interpreted internally, which allows 64k and 128k
>>>>>
>>>>> to work but not to 32k ?
>>>>>
>>>>> I would really appreciate, if anyone have any opinion on this.
>>>>>
>>>>> Regards,
>>>>> Cheleswer
>>>>>
>>>>>
>>>>>
>>>
>>