RFR: 8199717: Avoid calculating primordial thread stack bounds on VM startup

[Robbin Ehn]

Hi Claes, looks good.

Personally taste would be to instantiate the bool explicit (to true) like the 
other statics.

/Robbin

On 03/27/2018 12:02 PM, Claes Redestad wrote:
> Hi,
> 
> on linux, we scan /proc/self/maps to be able to tell if the current thread is 
> the "primordial" one.
> 
> However, when initializing the VM, all the java launchers spawn a new thread 
> rather than initializing the VM on the primordial thread, so we can deduce that 
> none of the threads we'll run on will be the primordial thread if started by one 
> of the standard java launchers. This enables us to skip reading the 
> /proc/self/maps entirely.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8199717
> 
> Webrev: http://cr.openjdk.java.net/~redestad/8199717/open.00/
> 
> This patch uses the Arguments::created_by_java_launcher(), which checks is the 
> sun.java.launcher property has been set or not. There is a small risk third 
> party launchers sets the sun.java.launcher property even when not conforming to 
> the behavior of the standard java launchers; if so the existing 
> created_by_java_launcher() method might need to be re-examined in a follow up.
> 
> This shaves ~0.7ms off of startup on my linux machine.
> 
> Thanks!
> 
> /Claes
>