Re: Null Stack Traces
On 1/29/2010 10:22 AM, Mark Smith wrote:
I just spend ages tracking down a null pointer exception that was
being thrown and not caught until somewhere near the top of the
application.
These types of errors do not have stack traces unfortunately.
That seems odd. Uncaught exceptions in finalizers are
discarded, and maybe there are one or two other such corner
cases, but in the ordinary course of events an uncaught
exception eventually makes its way back to the ultimate
catcher, which dumps whatever stack information is available.
This doesn't depend (as far as I know) on the nature of the
Throwable -- in particular, NullPointerException's stack
trace is not suppressed.
It sounds like there was a catch-and-ignore somewhere
along the line, in your application or in some framework it
was built around. That's one reason catch-and-ignore is a
Very Bad Idea.
To find it I had to hack my code to manually print out messages as it
entered and exited methods.
Are there any development tools for java that I can attach to my
process to get this kind of tracing without having to manually write
debugging info from code?
You might take a look at the java.lang.instrument package.
I haven't, not seriously, but it seems capable of this sort of
thing. (It also seems, at a cursory glance, to be considerably
more difficult than inserting println() calls.) Also, see if
your platform has a DTrace that can see inside Java code -- I
know the Solaris version does, but I'm not sure whether the
other DTrace platforms are as far along.
--
Eric Sosman
esosman@ieee-dot-org.invalid