[erlang-questions] erl_ddll bugfixes

[Bjorn Gustavsson]

Thanks for the bug report.

We read all emails but we are often slow to answer them.

In this case, we are in the progress of totally rewriting
the erl_ddll code for the R11B-2 release. The bugs you
mentioned will be corrected, as well as other issues.

/Bjorn

Jean-Sébastien Pédron <js.pedron@REDACTED> writes:

> * PGP Signed by an unknown key: 10/18/2006 at 05:33:41 PM
> 
> Hello,
> 
> Note: I posted a mail a week ago on erlang-patches@ about a bug in
> erl_ddll but didn't get any feedback so I try again here.
> 
> erl_ddll contains a bug with reference count. You'll find an example of
> it in my first mail:
> http://www.erlang.org/pipermail/erlang-patches/2006-October/000164.html
> 
> To sum up quickly the problem, ddll_server will only keep a reference
> for the first and the last processes who loaded a library. Every
> in-between process references will be dropped with each call to
> erl_ddll:load_driver/2.
> 
> The consequence is that if the first and the last processes unload the
> driver, the library will be effectively unloaded and every still running
> port drivers will become unusable.
> 
> Since then, I found another bug regarding the link established between
> ddll_server and the process who called erl_ddll:load_driver/2. This link
> exists only between ddll_server and the first process. Following
> processes who load the same library won't have a link and if they exit
> without calling erl_ddll:unload_driver/1, their reference in ddll_server
> will remain there until ddll_server terminates.
> 
> These two bugs exist at least from R10B-7 up to R11B-1.
> 
> --
> Jean-Sébastien Pédron
> Meetic Corp.
> 
> * Unknown Key
> * 0xC1583A53 (L)
> 
> --- otp_src_R11B-1-orig/lib/kernel/src/erl_ddll.erl	2006-05-03 09:59:12.000000000 +0200
> +++ otp_src_R11B-1/lib/kernel/src/erl_ddll.erl	2006-10-10 15:08:58.000000000 +0200
> @@ -164,8 +164,8 @@
>  
>  increment_process_count([{From, Count}|Rest], From, Result) ->
>      Result ++ [{From, Count+1}|Rest];
> -increment_process_count([Process|Rest], From, _Result) ->
> -    increment_process_count(Rest, From, [Process|Rest]);
> +increment_process_count([Process|Rest], From, Result) ->
> +    increment_process_count(Rest, From, [Process|Result]);
>  increment_process_count([], From, Result) ->
>      [{From, 1}|Result].
>  
> --- otp_src_R11B-1-orig/lib/kernel/src/erl_ddll.erl	2006-10-11 15:07:22.000000000 +0200
> +++ otp_src_R11B-1/lib/kernel/src/erl_ddll.erl	2006-10-11 15:05:33.000000000 +0200
> @@ -167,6 +167,7 @@
>  increment_process_count([Process|Rest], From, _Result) ->
>      increment_process_count(Rest, From, [Process|Rest]);
>  increment_process_count([], From, Result) ->
> +    link(From),
>      [{From, 1}|Result].
>  
>  %% Decrements the reference count for Driver in process From,
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-- 
Björn Gustavsson, Erlang/OTP, Ericsson AB