[erlang-questions] Process heap inspector
Björn-Egil Dahlberg
egil@REDACTED
Mon Nov 28 14:05:58 CET 2011
On 2011-11-28 12:11, Ahmed Omar wrote:
> I like the idea but i'm HORRIFIED about people misusing that and
> actually try to read internal states within their programs :D
I would put such a function in erts_debug:inspect_heap/1 instead.
// Björn-Egil
>
> On Mon, Nov 28, 2011 at 12:02 PM, Michal Ptaszek
> <michal.ptaszek@REDACTED
> <mailto:michal.ptaszek@REDACTED>> wrote:
>
> Hey,
>
> good point, I knew I forgot about something - will add support for
> that
> really soon.
>
> Kind regards,
> Michal Ptaszek
>
> On Nov 28, 2011, at 11:02 AM, Attila Rajmund Nohl wrote:
>
> > Hello!
> >
> > I really like the idea. But shouldn't this list include the
> message queue too?
> >
> > 2011/11/28 Michal Ptaszek <michal.ptaszek@REDACTED
> <mailto:michal.ptaszek@REDACTED>>:
> >> Hi everyone,
> >>
> >> This idea was born in my mind when debugging some complex, live
> system
> >> and trying to figure out where did all my memory go.
> >>
> >> So, when debugging live system/investigating suspicious memory
> consumption patterns
> >> or simply trying to understand better what's going on with our
> processes, it might be useful
> >> to take a peep at the data given process operates on.
> >>
> >> Right now it is possible to fetch internal gen_* processes
> state via sys:get_status, we can do
> >> some tracing (even using DTrace), we can also check
> erlang:process_info output and analyze
> >> it to become more or less familiar with what is the heap size
> of our suspect. Still, not all processes
> >> are OTP-compatible, and even if: we are going to get only
> "alive" data coming from process' state
> >> (not counting the outdated, not yet garbage collected terms).
> Also, process_info informs us only
> >> about allocated size of the heap, not about the actual usage
> (although the pre-allocated chunks
> >> are not available to the system, yet we might see how far we
> are from growing/shrinking it).
> >>
> >> Enough with introduction, let's focus on the actual meat: my
> idea was to create a new BIF,
> >> namely erlang:inspect_heap(Pid) that allows us to take a look
> at any process' heap, fetch the
> >> terms residing there and check their actual size. So, for instance:
> >>
> >>> (ejabberd@REDACTED)12> S = erlang:inspect_heap(pid(0, 358, 0)).
> >>> [{[[<<"5">>]|
> >>>
> 284735200226724471091958640173737944785062822211005333957298336375301959844499896296764925551414319236776784],
> >>> 20},
> >>> {{'$internal_queue_len',0},3},
> >>> {{random_seed,{8236,26623,17360}},7},
> >>> {{'$ancestors',[ejabberd_c2s_sup,ejabberd_sup,<0.40.0>]},9},
> >>> {{'$initial_call',{gen,init_it,6}},7},
> >>> {{state,{socket_state,tls,
> >>> {tlssock,#Port<0.3936>,#Port<0.3938>},
> >>> <0.357.0>},
> >>> ejabberd_socket,#Ref<0.0.0.10120>,false,<<"2855118401">>,
> >>> {sasl_state,"jabber",<<"pvp.net <http://pvp.net>">>,[],
> >>>
> #Fun<ejabberd_c2s.0.67315917>,#Fun<ejabberd_c2s.1.67315917>,
> >>> #Fun<ejabberd_c2s.2.67315917>,cyrsasl_digest,
> >>> {state,5,<<"3598825873">>,
> >>> {<<"dupa">>,<<...>>},
> >>> <<>>,#Fun<ejabberd_c2s.0.67315917>,...}},
> >>> true,
> >>> {jid,<<"dupa">>,<<"pvp.net
> <http://pvp.net>">>,<<"hubbard">>,<<"dupa">>,
> >>> <<"pvp.net <http://pvp.net>">>,<<"hubbard">>},
> >>> <<"Nicknamedupa">>,
> >>> {{1322,217197,749816},<0.358.0>},
> >>> {1,{<<"dupa">>,nil,nil}},
> >>> {1,{<<"dupa">>,nil,nil}},
> >>> {1,{<<"dupa">>,nil,nil}},
> >>> {xmlelement,<<"presence">>,[],
> >>>
> [{xmlcdata,<<...>>},{xmlelement,...},{...}|...]},
> >>> {userlist,none,[],false}},
> >>> 564},
> >>> {{limits,undefined},3},
> >>> {{[],[]},3}]
> >>
> >> gives us a pretty good knowledge on <0.358.0>:
> >> . '$_' - OTP + gen_fsm2 process dictionary stuff, 3, 9, 7 words
> each
> >> . random_seed - obvious
> >> . {{limits,undefined},3} - internal limits for gen_fsm2 message
> queue, 3 words
> >> . {[], []} - most probably leftovers after fetching user's
> presence lists
> >> . {state, _} - gen_fsm2 state record - 564 words
> >> . {[[<<"5">>]|, ...} - sequential tracing tokens? (I'm not very
> familiar with that, I would
> >> say that's something from our rootset
> >>
> >> The implementation is rather simple: if the process we probe is
> not the caller one (we are not doing
> >> erlang:inspect_heap(self()), the data is copied from the callee
> heap to caller heap (to prevent from having
> >> cross-process references in variables), then we compute flat
> size of the each term we moved. Also, rootset
> >> is also included in the summary (i.e. process dict, seq tokens,
> etc.).
> >>
> >> Code is included in my inspect_heap OTP branch on:
> >> github: https://github.com/paulgray/otp/tree/inspect_heap
> >>
> >> I am still a little bit hesitant about suspending process we
> probe: can anyone tell
> >> me if acquiring main process lock would be enough to keep its
> heap untouched during
> >> the call?
> >>
> >> Please, do point any bugs and tell me what do you think about
> the idea.
> >>
> >> Best regards,
> >> Michal Ptaszek
> >> _______________________________________________
> >> erlang-questions mailing list
> >> erlang-questions@REDACTED <mailto:erlang-questions@REDACTED>
> >> http://erlang.org/mailman/listinfo/erlang-questions
> >>
>
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>
>
> --
> Best Regards,
> - Ahmed Omar
> http://nl.linkedin.com/in/adiaa
> Follow me on twitter
> @spawn_think <http://twitter.com/#%21/spawn_think>
>
>
>
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