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Luna
Posted: Fri Dec 01, 2006 1:29 pm Reply with quote
User Joined: 27 Feb 2005 Posts: 23
I'm wasting a really good obfuscated Erlang contribution here...

See code below.

qlc "A" works if you remove ", true".

Both work if you remove disc_only_copies.

This error occurs in R11B-2, but not in R11B-1.

/Daniel Luna

%% -*- erlang-indent-level: 2 -*-
-module(qlc_bug).
-compile(export_all).

-include_lib("stdlib/include/qlc.hrl").

provoke_error()->
application:set_env(mnesia,dir,"/tmp/"),
mnesia:create_schema([node()]),
ok = mnesia:start(),
case mnesia:create_table(blah,
[{disc_only_copies,[node()]},
{type,set}]) of
{atomic,ok} -> ok; {aborted,{already_exists,blah}} -> ok
end,

A= qlc:q([F || F <-mnesia:table(blah), (F band ((1 bsl 0)) =/= 0), true]),
{atomic,Result} = mnesia:transaction(fun() -> qlc:eval(A)end),
case is_list(Result) of
true -> io:format("List~n",[]);
false -> io:format("This should not happen!~nResult = ~p~n",[Result])
end,

B = qlc:q(["" || I <- mnesia:table(blah), any:function_call(I)]),
{atomic,BR} = mnesia:transaction(fun()->qlc:eval(B)end),
case is_list(BR) of
true -> io:format("List~n",[]);
false -> io:format("This should not happen!~nResult = ~p~n",[BR])
end.

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Guest
Posted: Fri Dec 08, 2006 7:48 am Reply with quote
Guest
[Daniel Luna:]
> See code below.
>
> qlc "A" works if you remove ", true".
>
> Both work if you remove disc_only_copies.
>
> This error occurs in R11B-2, but not in R11B-1.

Thanks for the bug report.

It seems that a modification in R11B-2 exposed a bug that has been
present for quite some time. The bug was triggered by the empty Dets
table, but could also show up when no object matches a given match
specification.

The following patch ensures that dets:match{_object}() and
dets:select() never return {[],Cont} which should solve the problem at
hand.

*** /usr/local/otp/releases/otp_beam_solaris8_r11b_patched/lib/stdlib-1.14.2/src/dets.erl Thu Nov 16 17:40:35 2006
--- dets.erl Wed Dec 6 12:43:19 2006
***************
*** 718,723 ****
--- 718,725 ----
false ->
badarg
end;
+ [] ->
+ chunk_match(NewState);
Terms ->
{Terms, NewState}
end;

The patch erl_898_otp_beam is available at the Licencees' Area
(http://www.erlang.se/lic_area/index.shtml).

Best regards,

Hans Bolinder, Erlang/OTP
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