[erlang-bugs] Allow code upgrade for the code_server itself

[Siri Hansen]

Hi Stavros!

2014-06-23 11:48 GMT+02:00 Stavros Aronis <aronisstav@REDACTED>:

a lot of time has passed indeed, and I have put in place a different kind
> of instrumentation, which works for what I want to do. Unfortunately I
> currently don't have the time to test again, but I suspect that the issue
> remains, for the reasons I explained.
>

Yes, I assume nothing has changed - my point was that when receiving a
change_code system message, code_server does a qualified call to
system_code_change. This is where the actual code change is expected to
happen - not in the call to system_continue at line 184.

I would think that the reason that sys uses a qualified call is that the
module in question is not ?MODULE, but rather a callback.


>
> Here is another bug, admittedly unrelated (since I am not trying to update
> the code of the code_server *process*):
>
> 1) Copied code_server.erl to my home directory and added an
> "erlang:display(foo)" call before the single erlang:load_module/1 call in
> the module.
> 2) Run the following:
> $ erlc code_server.erl
> $ erl -nostick
> Erlang/OTP 17 [erts-6.0] [source-07b8f44] [64-bit] [smp:8:8]
> [async-threads:10] [hipe] [kernel-poll:false]
>
> Eshell V6.0  (abort with ^G)
> 1> l(code_server).
> {module,code_server}
> 2> code:which(code_server).
> "/home/stavros/code_server.beam"
> 3> erlang:check_old_code(code_server).
> true
> 4> code:soft_purge(code_server).
> true
> 5> l(te *TAB*
> Crash dump was written to: erl_crash.dump
> Internal error: Invalid reference count found on #Fun<code_server.0.416>:
>  About to erase fun still referred by code.
> Aborted
>
> I would expect the soft_purge to fail and the system not to crash.
>

Yes, I would also expect that. And I can not reproduce the problem :(

$ erlc code_server.erl
$ erl -nostick
Erlang/OTP 17 [erts-6.0] [source-07b8f44] [smp:4:4] [async-threads:10]
[hipe] [kernel-poll:false]

Eshell V6.0  (abort with ^G)
1> l(code_server).
{module,code_server}
2> code:which(code_server).
"/home/siri/code_server.beam"
3> erlang:check_old_code(code_server).
true
4> code:soft_purge(code_server).
false

I also have
5> erlang:check_process_code(whereis(code_server),code_server).
true

Do you have any other patches, or is it a plain 17.0? (Sorry - I don't have
any other ideas right now :( )

/siri


>
> On Thu, Jun 19, 2014 at 11:26 AM, Siri Hansen <erlangsiri@REDACTED>
> wrote:
>
>> Hi Stavros, I'm sorry for the very long delay! Are you still struggling
>> with this problem or did you find a way around it? Would a code_change
>> system message while the process is suspended possibly solve the problem?
>> Regards
>> /siri
>>
>>
>> 2014-03-10 23:02 GMT+01:00 Stavros Aronis <aronisstav@REDACTED>:
>>
>>> Hello!
>>>
>>> I am playing around with code instrumentation and trying to hack the
>>> code server so that it applies some transformation whenever it loads *any*
>>> module. The hack itself is relatively simple:
>>>
>>> 1) Instrument and reload any already loaded modules (come to think about
>>> it, during this process more modules may be loaded, but let's assume a
>>> fixpoint). This is to avoid the case where in order to load A, you have to
>>> instrument A, and the instrumenter itself needs a call to X, which is not
>>> yet loaded so you have to load X, so you have to instrument X, etc...
>>> 2) Get the Core Erlang code of the codeserver and wrap the second
>>> argument of erlang:load_module (Line 1264) with a call to my instrumenter
>>> (which is a function from binary() -> binary())
>>> 3) Load the patched code_server code
>>> 4) Move the code_server process from the old code to the new one.
>>>
>>> I am having trouble with the last step. As far as I understand it, the
>>> reason is that the call to system_continue (Line 184) is not qualified, as
>>> is the similar call in sys.erl (Line 324).
>>>
>>> Is there a reason why this is so? Is there any possibility for this to
>>> be patched?
>>>
>>> Cheers,
>>>
>>> Stavros
>>>
>>>
>>> _______________________________________________
>>> erlang-bugs mailing list
>>> erlang-bugs@REDACTED
>>> http://erlang.org/mailman/listinfo/erlang-bugs
>>>
>>>
>>
>
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