HotSpot Serviceability Agent for BSD

[Greg Lewis]

G'day Swamy,

On Wed, Feb 04, 2009 at 04:22:26PM -0600, Swamy Venkataramanappa wrote:
> Hi Greg and Brain,
> 
> Thanks for porting the Serviceability Agent for BSD.  I briefly looked 
> at the patch code and it looks
> good.   Regarding issue #1. I suspect the problem is in the detach code:
> 
> +// detach all pids of a ps_prochandle
> +static void detach_all_pids(struct ps_prochandle* ph) {
> +  thread_info* thr = ph->threads;
> +  while (thr) {
> +     ptrace_detach(thr->lwp_id);
> +     thr = thr->next;
> +  }
> +}
> 
> On linux we need to call ptrace(DETACH) for all the threads. This not 
> required for other unix
> OS. It depends on how threads are implemented in the OS. I guess for BSD 
> you just need to
> call ptrace(DETACH)  for process id once. 
> I am currently maintaining the Serviceability agent code at Sun. If you 
> need any help let me
> know.

Thanks!  This is definitely part of the puzzle.  I tried replacing the
loop with a ptrace_detach(ph->pid), but now the process segfaults rather
than dying.  I think a review of the ptrace calls is in order :).

> Brian Gardner wrote:
> > Great Greg,
> > I'll check out #1 for you later in the week after I release another 
> > version of my openjdk6 patch.  :)
> >
> > Brian
> >
> > Greg Lewis wrote:
> >   
> >> I've been toying with the idea of porting the HotSpot Serviceability Agent
> >> (http://openjdk.java.net/groups/hotspot/docs/Serviceability.html) to BSD
> >> for a while now.
> >>
> >> Brian Gardner's work on getting jmap -dump and jmap -histo to work for
> >> FreeBSD's jdk16 port catalysed this.  A work in progress patch is
> >> available at http://www.eyesbeyond.com/freebsddom/java/saproc.diff
> >> This allows me to use the other jmap options (-finalizerinfo, -heap,
> >> -permstat) and allows jinfo to work.  It should also get jsadebugd
> >> to work, but I haven't tried that yet.
> >>
> >> The patch is for OpenJDK7 and includes changes based in part on
> >> Brian's work (so jmap -dump and jmap -histo work as well).
> >>
> >> There are some serious caveats so far though.
> >>
> >> 1. The Java process being attached to appears to be killed after the
> >>    attachment completes.  So I can, for example, run 'jmap -permstat <pid>'
> >>    and get the expected output, but then <pid> dies.  I haven't looked
> >>    into this yet, but its obviously a big problem :).
> >>
> >> 2. It works on FreeBSD 7.x only since it uses the undocumented
> >>    kinfo_getvmmap function to look up information about the shared
> >>    libraries that the process has open.  I suspect we can do something
> >>    with libkvm for OpenBSD and NetBSD.  Anyone know how to do this on
> >>    Mac OS X?  On Linux (which is what I ported against) this is done
> >>    by looking at /proc/<pid>/maps.  Better suggestions?
> >>
> >> 3. It includes the hsearch_r source from GNU libc since BSD doesn't have
> >>    this.  I don't think this is a problem license wise, but in case it is
> >>    I think we can come up with something similar that is available on
> >>    BSD.  I just grabbed it 'cos it was simpler at the time to keep things
> >>    as close to the Linux version as was reasonable.
> >>
> >> For me this moves us towards closing one of our only feature gaps (as I
> >> see it).  But it definitely needs some more review and fixing, so all
> >> comments, patches, etc. appreciated.
> >>
> >>   
> >>     
> >
> >   

-- 
Greg Lewis                          Email   : glewis at eyesbeyond.com
Eyes Beyond                         Web     : http://www.eyesbeyond.com
Information Technology              FreeBSD : glewis at FreeBSD.org