[foreign] RFR: 8227125: java/foreign/pthread/Threads.java asserts on debug build

[Nick Gasson]

Hi,

The fix for 8226250 checks the result of JavaThread::current() for NULL 
to see if this thread is attached to the VM or not. But this function 
will assert on a debug build rather than return NULL. This patch uses 
Thread::current_or_null() instead which allows a NULL result.

Made this change in both the universal upcall handler and the direct 
fast-path. The universal handler also has an issue where 
JavaCallArguments will do an allocation if the number of arguments is 
greater than 8. But when the thread has just attached to the VM there is 
no ResourceMark on the stack to associate the allocation with. I changed 
the test to run a second time without the fast-path to catch this.

Bug: https://bugs.openjdk.java.net/browse/JDK-8227125
Webrev: http://cr.openjdk.java.net/~ngasson/foreign/8227125/webrev.0/

Thanks,
Nick