[erlang-questions] Feedback wanted: Remove compilation times from BEAM files in OTP 19?

Richard Carlsson carlsson.richard@REDACTED
Fri Apr 8 22:42:07 CEST 2016

Hi Serge (and everyone else)! I've actually got an improved version of that
module change detection (i.e., based on md5) that I was going to clean up
and submit to OTP as a standard part of the shell. I think the original
snippets have been drifting around on the interwebs for aeons, and I'm not
sure who wrote them originally. We've been using them at Klarna forever.
But we needed something more reliable (that works even if you have made a
completely new build of every module, but not actually changing more than a
few), so I started by pushing some patches to OTP that made the md5 of
loaded modules easily available in module_info. Then based on that I wrote
an improved shell function like you just did - we've now tried it out for a
while and found it stable, so it's a good time to push this as well.

I think my only hesitation is where to put the core "module changed"
functionality if I'm to submit it as part of OTP: the code module?
beam_lib? somewhere else? Any opinions out there?


2016-04-08 15:37 GMT+02:00 Serge Aleynikov <serge@REDACTED>:

> ​Thank you!
> I updated the
> https://github.com/saleyn/util/blob/master/src/user_default.erl per your
> suggestion.
> On Fri, Apr 8, 2016 at 8:54 AM, Björn Gustavsson <bjorn@REDACTED> wrote:
>> On Fri, Apr 8, 2016 at 2:28 PM, Serge Aleynikov <serge@REDACTED>
>> wrote:
>> > I've been relying on module's compilation time for figuring out the
>> changed
>> > modules (see below).
>> >
>> > In the absence of {time, CompileTime}, would there be a way to
>> determine the
>> > modification time stamp of the file at the time it was loaded by code
>> > loader?
>> Yes. Use Mod:module_info(md5) to calculate MD5 for
>> the loaded module and compare it to beam_lib:md5(Mod).
>> Example:
>> 13> c:module_info(md5).
>> <<79,26,188,243,168,60,58,45,34,69,19,222,138,190,214,118>>
>> 14> beam_lib:md5(code:which(c)).
>> {ok,{c,<<79,26,188,243,168,60,58,45,34,69,19,222,138,
>>          190,214,118>>}}
>> /Bjorn
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