[erlang-questions] how to _cause_ a code_change in a gen_fsm

Daniel Dormont <>
Sat Nov 26 18:01:03 CET 2011


Ok. So what is the "right" way to get my code_change callback to fire?
I see some reference to "appup" and I have looked over that part of
the manual but don't really understand how it applies to my case.
Literally all I have is a .beam file I want to install in a running
system.

dan

On Sat, Nov 26, 2011 at 10:28 AM, Bob Ippolito <> wrote:
> I don't know how ejabberd likes to do things but l() is the lower level
> non-OTP way to do things and will immediately purge the old code and load
> the new code. Nothing else will happen, no magic.
>
> On Friday, November 25, 2011, Daniel Dormont <>
> wrote:
>> This is a follow-up to my earlier question but the topic is a little
>> different. Having put together a nice piece of code for handling the
>> change in my gen_fsm's state record, I discovered to my chagrin that
>> when I loaded the new code (using l() at first and then using the
>> "update" command that comes with ejabberd) it did not call the
>> code_change callback; neither immediately nor before processing the
>> next message sent to that process. I admit that the details of things
>> like proc_lib and sys are a little opaque to me, but I had understood
>> that as long as the module implemented a standard OTP behavior, code
>> upgrades would "just work" in some sense. I suppose I was wrong :)
>> This module is fairly self-contained, so I'm not too worried about
>> having to synchronize other modules, notify supervisors or anything
>> like that. How do I proceed from here?
>>
>> thanks,
>> dan
>>
>>
>> ---------- Forwarded message ----------
>> From: Daniel Dormont <>
>> Date: Mon, Nov 21, 2011 at 10:51 AM
>> Subject: code_change for gen_fsm: how to actually handle a state change
>> To: erlang-questions <>
>>
>>
>> Hello all,
>>
>> I have a gen_fsm module and would like to take advantage of hot code
>> deploy. The module uses a record (called "state") and the new version
>> of the module includes some new fields in the record. What is a nice
>> clean way to code the my_module:code_change function to deal with
>> this? Are there any good examples out there on the web?
>>
>> Note: for my purposes it would be sufficient to detect that the state
>> record is out of date, and terminate cleanly. BUT the correct
>> functionality of the terminate/3 function in my module depends on the
>> state data, and I would need it to complete cleanly and not crash in
>> this instance because there are other processes that depend on this
>> one and need to be notified properly of its exit. The issue is that
>> the state itself contains the data of which processes those are.
>>
>> What's the best approach here?
>>
>> thanks,
>> Dan
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