RFR(XS): VM times out in VM_HandshakeAllThreads::doit() with RunThese30M

[Robbin Ehn]

Hi Dan, thanks,

On 2018-08-15 22:02, Daniel D. Daugherty wrote:
> So if HandshakeState::vmthread_can_process_handshake() is only
> called by the VMThread while at a safepoint, then the target
> JavaThread cannot be externally resumed while that function is
> running so this new check:

No we are not at safepoint, this method is never called at safepoint. All
other threads should be considered running. Therefore I need to stop resuming 
targeted suspended thread while VM thread is executing the handshake on behalf 
of the suspended thread.

Does my comment/assert make more sense in the light of that?

/Robbin

> 
>    +  return SafepointSynchronize::safepoint_safe(target, 
> target->thread_state()) ||
>    +         target->is_ext_suspended();
> 
> is okay because that externally suspended thread is also safepoint safe.
> 
> This assert:
> 
> +  assert(Threads_lock->owned_by_self(), "Not holding Threads_lock.");
> 
> doesn't quite match your intent. If 
> HandshakeState::vmthread_can_process_handshake()
> should only be called by the VMThread at a safepoint, then a different
> check would be better:
> 
>    assert(SafepointSynchronize::is_at_safepoint() && 
> Thread::current()->is_VM_thread(),
>           "must be VMThread at a safepoint");
> 
> Perhaps this for your comment:
> 
>    // SafepointSynchronize::safepoint_safe() does not consider an externally
>    // suspended thread to be safe. However, if we are at a safepoint, then
>    // the externally suspended thread cannot be resumed so it is safe.
> 
> Dan
> 
> 
>>
>> Thanks, Robbin
>>
>>>
>>> Thanks,
>>> David
>>>
>