Need help to understand TLS behavior

[cheleswer sahu]

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

/jdk8u-cpu <https://java.se.oracle.com/source/xref/jdk8u-cpu/>/jdk 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/>/src 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/>/solaris 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/>/classes 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/>/java 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/>/lang 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/>/UNIXProcess.java 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java>

227 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java#227>             ThreadFactory 
<https://java.se.oracle.com/source/s?defs=ThreadFactory&project=jdk8u-cpu>  threadFactory 
<https://java.se.oracle.com/source/s?defs=threadFactory&project=jdk8u-cpu>  =grimReaper 
<https://java.se.oracle.com/source/s?defs=grimReaper&project=jdk8u-cpu>  -> {
228 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java#228>                 // Our thread stack requirement is quite modest.
229 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java#229>                 Thread <https://java.se.oracle.com/source/s?defs=Thread&project=jdk8u-cpu>  t =*new*  Thread <https://java.se.oracle.com/source/s?defs=Thread&project=jdk8u-cpu>(systemThreadGroup 
<https://java.se.oracle.com/source/s?defs=systemThreadGroup&project=jdk8u-cpu>,grimReaper 
<https://java.se.oracle.com/source/s?defs=grimReaper&project=jdk8u-cpu>,
230 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java#230>                                       "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 <https://java.se.oracle.com/source/s?defs=Thread&project=jdk8u-cpu>  t =*new*  Thread <https://java.se.oracle.com/source/s?defs=Thread&project=jdk8u-cpu>(systemThreadGroup 
<https://java.se.oracle.com/source/s?defs=systemThreadGroup&project=jdk8u-cpu>,grimReaper 
<https://java.se.oracle.com/source/s?defs=grimReaper&project=jdk8u-cpu>,
230 
<https://java.se.oracle.com/source/xref/jdk8u-cpu/jdk/src/solaris/classes/java/lang/UNIXProcess.java#230>                                       "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