Is it possible to stop a specific application thread?

[Keith Chapman]

On Tue, Nov 12, 2013 at 3:24 AM, Lindenmaier, Goetz <
goetz.lindenmaier at sap.com> wrote:

> Hi,
>
> our VM is running with what we call PerThreadSafepoints for a long time.
>
> We implement this by loading the page from the thread as you propose.
> But we don't have a page per thread, as poisoning them seems to costly
> if there are many threads and all threads must be stopped.
>
> Instead, we adapt the field in the thread: usually it points to some
> valid address.  If a safepoint is required, the polling page is written
> into that field.
>
> We implemented this when we tried to improve BiasedLocking,
> but as we could not gain anything, we don't really use it any more.
>
> If you really have interest in this feature, I can prepare a webrev
> for it.
>

That would be awesome.


>
> Best regards,
>   Goetz.
>
> -----Original Message-----
> From: hotspot-dev-bounces at openjdk.java.net [mailto:
> hotspot-dev-bounces at openjdk.java.net] On Behalf Of Keith McGuigan
> Sent: Dienstag, 12. November 2013 06:46
> To: David Holmes
> Cc: hotspot-dev at openjdk.java.net
> Subject: Re: Is it possible to stop a specific application thread?
>
> I had a prototype at one point that did #2, but I don't have the source for
> it anymore. If Karen or Coleen kept a copy of my workspace, perhaps they
> can reply with the diffs to give someone a leg up in doing this again.
>
> --
> - Keith (McGuigan)
>
> On Monday, November 11, 2013, David Holmes wrote:
>
> > On 12/11/2013 11:16 AM, Keith Chapman wrote:
> >
> >> Hi David,
> >>
> >> On Mon, Nov 11, 2013 at 7:26 PM, David Holmes <david.holmes at oracle.com
> >> <mailto:david.holmes at oracle.com>> wrote:
> >>
> >>     Hi Keith,
> >>
> >>
> >>     On 12/11/2013 6:29 AM, Keith Chapman wrote:
> >>
> >>         Hi,
> >>
> >>         I'm playing around with some research ideas on hotspot.
> >>
> >>         One of my runtime services of the VM needs to stop a specific
> >>         application
> >>         thread (I have a handle to the pthread of the application
> >>         thread). How can
> >>         the VM stop such a thread? Is there any mechanism in place to do
> >>         this?
> >>
> >>
> >>     There is no general purpose mechanism currently in place.
> >>
> >>
> >> Thats a bummer, having such a mechanism would have been useful for
> >> numerous VM services like biased locking revocation, concurrent GC.
> >>
> >
> > For which safepoints are generally used so a per-thread safepoint
> > mechanism is what you are looking for.
> >
> >
> >>     You could use the deprecated and inherently dangerous Thread.suspend
> >>     mechanism (either directly or via the JVMTI suspension interface).
> >>
> >>     Or if you are more adventurous with your VM hacking you could
> >>     introduce a per-thread safepoint operation to cause it to stop.
> >>
> >>
> >> I actually thought about that and explored the way safepoints are
> >> implemented. The place that I had most trouble was getting threads
> >> running compiled code to stop. The way it currently works is by
> >> allocating a polling page (at startup) and drilling in that address into
> >> the compiled code. Hence i I am to do it per thread I would have to make
> >> a call to the runtime to get the address of the polling page for that
> >> particular thread. I presume this would be too expensive (Making a VM
> >> call at the end of each method and through some loop iterations).
> >>
> >> Is there any insight you could offer on how this could be done?
> >>
> >
> > Two basic options I can think of:
> >
> > 1. Use a single shared page and have other threads simply ignore the
> > safepoint request. This might incur some overhead as not-wanted threads
> > could hit this multiple times.
> >
> > 2. Use a per-thread page accessed via the current thread. There would be
> a
> > little overhead for the indirection but the compiler knows how to access
> > the current JavaThread object. No need for runtime calls that I can see.
> >
> > Good luck.
> >
> > David
> >
> >  Thanks,
> >> Keith.
> >>
> >>     Or you could hack in a special "magic exception" type the processing
> >>     of which simply blocks the thread until "resumed" somehow (not sure
> >>     how ??). Or ...
> >>
> >>     Cheers,
> >>     David
> >>
> >>         Thanks,
> >>         Keith.
> >>
> >>
> >>
> >>
> >> --
> >>
> >> Keith Chapman
> >> blog: http://www.keith-chapman.org
> >>
> >
>



-- 

Keith Chapman
blog: http://www.keith-chapman.org