hprof format question

[Simon Roberts]

Ah, my apologies, many thanks for the guidance. I'll try there.

On Wed, Oct 31, 2018 at 10:41 AM Magnus Ihse Bursie <
magnus.ihse.bursie at oracle.com> wrote:

> Hi Simon,
>
> On 2018-10-24 00:26, Simon Roberts wrote:
> > Hi all, I'm hoping this is the correct list for a question on the hprof
> > file format (1.0.2)?
> I don't think it is. You might get better response from
> serviceability-dev at openjdk.java.net.
>
> /Magnus
>
> >
> > I found this information:
> >
> http://hg.openjdk.java.net/jdk6/jdk6/jdk/raw-file/tip/src/share/demo/jvmti/hprof/manual.html
> >
> > and have been working on a small project to read these files. (Yes, I
> know
> > that NetBeans/VisualVM and Eclipse both have such libraries, and a number
> > of other tools have been derived from those, but so far as I can tell,
> they
> > all are fundamentally built on the notion of fully decoding everything,
> and
> > creating memory representations of the entire heap. I want to pull out
> only
> > certain pieces of information--specifically object counts by class--from
> a
> > large, ~20Gb, dump file, and those tools just give up the ghost on my
> > systems.)
> >
> > Anyway, my code reads the file pretty well so far, except that the file I
> > want to analyze seems to contradict the specifications of the document
> > mentioned above. Specifically, after processing about five
> > HEAP_DUMP_SEGMENTS with around 1.5 million sub-records in each, I come
> > across some ROOT_JNI_LOCAL records. The first 15 follow the format
> > specified in the above document (one 8 byte "ID" and two four byte
> values.)
> > But the 16th omits the two four byte records (well, it might simply have
> > more, but visual analysis shows that after the 8 byte ID, I have a new
> > block tag, and a believable structure.
> >
> > My current intention is to write a "smart" parser that investigates
> whether
> > processing will succeed or not if the "normal" format is read, or will
> use
> > the alternate format if it realizes that it would result in the next
> block
> > starting with an illegal tag value. Clearly this is not ideal!
> >
> > Is there any more detailed, newer, better, information? Or anything else
> I
> > should know to pursue this tool (or indeed a simple object frequency by
> > classname result) from an hprof 1.0.2 format file?
> >
> > (And yes, I'm pursuing a putative memory leak :)
> >
> > Thanks for any input (including "dude, this is the wrong list!")
> > Cheers,
> > Simon
> >
> >
> >
>
>

-- 
Simon Roberts
(303) 249 3613