Instrumenting Erlang code

[Michael Truog]

On 1/26/20 4:58 AM, Frank Muller wrote:
> Hi everyone
>
> I would like to implement a custom instrumentation module for my 
> Erlang code.
> Let assume this function:
>
You are describing that you need aspects from aspect oriented 
programming (that should be the best concept for what you want, when 
thinking about the problem).  I implemented this in CloudI 
(https://cloudi.org) as a list of functions that are executed in order 
with separate lists for before and after a callback function.  My 
approach used the following to represent a function [1]:

{Module :: atom(), Function :: atom()}

to represent a function of the expected arity (call it arity N), and:

{{Module :: atom(), Function :: atom()}}

to represent a function of arity 0 that returns a function of arity N, 
or a normal Erlang function.  Representing the function as a tuple with 
atoms allows specifying the function before it is loaded.  Using the 
arity 0 function indirection allows execution of source code before the 
function is created, normally when a function retains variables created 
before the function is created (a closure).  Using this approach made it 
easy to add monitoring to CloudI services and other things like batch 
execution of CloudI services.

Using functions as data (configuration for the source code [2]) avoids 
source code that lacks transparency, like macros or parse transforms.

Best Regards,
Michael

[1] Example type specification 
https://github.com/CloudI/CloudI/blob/7cac9108827ce58008eac7aa24e192c44e2fbfd6/src/lib/cloudi_core/src/cloudi_service_api.erl#L203-L205
[2] Example configuration of aspects 
https://github.com/CloudI/CloudI/blob/7cac9108827ce58008eac7aa24e192c44e2fbfd6/src/lib/cloudi_core/src/cloudi_service_api.erl#L429-L434
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