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From "Leo Li" <liyilei1...@gmail.com>
Subject Re: [launcher] Uncaught exceptions not printed on J9 VME
Date Mon, 15 Oct 2007 06:59:51 GMT
On 10/15/07, Alexey Varlamov <alexey.v.varlamov@gmail.com> wrote:
> 2007/10/15, Alexey Varlamov <alexey.v.varlamov@gmail.com>:
> > 2007/10/14, Gregory Shimansky <gshimansky@apache.org>:
> > > Oliver Deakin wrote:
> > > > Hi all,
> > > >
> > > > A little while back there was a thread called "[drlvm] Should the
> > > > launcher print uncaught exceptions?" [1] where we discussed the fact
> > > > that running a test case like [2] did not print a stack trace with the
> > > > Harmony launcher. As part of this discussion, HARMONY-1819 was raised
> > > > and the line "(*jvm)->DetachCurrentThread(jvm)" was added to the
> > > > launcher main.c in repo revision r464443.
> > > >
> > > > HARMONY-3713 was later raised pointing out that calling
> > > > DetachCurrentThread() to detach the main thread was contrary to the spec
> > > > [3], and the line was removed from main.c. However, I have just noticed
> > > > that if you run [2] on the current J9 VME (and, in fact, on the RI with
> > > > a simple launcher) you do not get any stack trace printed, and I imagine
> > > > this has been the case since the commit of HARMONY-3713.
> > > >
> > > > The RI has a bug [4], contrary to the spec [3], which requires
> > > > DetachCurrentThread() to be called by the invoking launcher if you wish
> > > > to see the stack trace of an uncaught exception. It appears that J9 has
> > > > matched this bug, probably so no unexpected trace is printed in
> > > > launchers programmed against the RI.
> > > >
> > > > So currently running Harmony classlib with the J9 VME will not result
in
> > > > any stack trace being printed for uncaught exceptions, which makes
> > > > debugging issues where that occurs more troublesome. Id like to propose
> > > > that the DetachCurrentThread() line be readded to main.c (i.e. the
> > > > opposite of the patch for HARMONY-3713), perhaps with a comment to show
> > > > that this is to match the behaviour of the RI rather than the spec.
> > > >
> > > > Any objections?
> > >
> > > I wonder if simply adding
> > >
> > > if ((*env)->ExceptionCheck(env))
> > >     (*env)->ExceptionDescribe(env);
> > >
> > > is enough to print out stack trace in the main thread without violating
> > > the spec.
> > >
> >
> > The bug of RI [4] (fixed in 1.5) being referred by Oliver is a bit
> > wider than just printing out the stack trace. Synopsis reads:
> > "(thread) setUncaughtExceptionHandler() doesn't work on main thread ".
> > I believe this is really strong argument to use DetachCurrentThread
> > and be compatible with RI rather than spec (which should be fixed and
> > will be someday ;)
>
> FYI, spec is indeed fixed in 1.6 :
> http://java.sun.com/javase/6/docs/technotes/guides/jni/spec/invocation.html#wp16553

The clue from the change in spec is enough to show that it is
appropriate to call  DetachCurrentThread() in the main thread when
shutdowning VM.

>
> > Moreover, I suggest to add a regression test for this issue (like the
> > one in [4]) so the decision would stay locked in.
> >
> > [4] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4992454
> > --
> > Alexey
> >
> > >
> > > --
> > > Gregory
> > >
> > >
> >
>


-- 
Leo Li
China Software Development Lab, IBM

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