Hello,
I am currently trying to write a multi-format (JSON and msgpack)
multi-transport (TCP, Unix ports, file ports) RPC server and client egg for
Chicken. I have a decent architecture for my program (I think) but I
currently face an inexplicable bug that randomly appear and that I cannot
explain.
I used a simple actor model to handle concurrency in a clean way: actors
communicate through message passing and handle their internal states in a
single thread so that race conditions are impossible. To implement this
model I used srfi-18 threads, mailbox and COOPS classes. An actor is an
instance of a class inheriting from the <actor> base class I defined. It
loops over its mailbox and run actions for each message it received.
The software isn't complete yet but I am working on the test suite to
validate the features before going any further. Here is my problem:
When I am running the test suite I run the server on a separate thread (for
now each actor of the server is on another thread too) and I try to send
messages. however, I got the following error:
Warning (#<thread: sch>): in thread: (mailbox-send!) bad argument type -
not a mailbox: #f
Call history:
src/main/actor.scm:37: mailbox#mailbox-send! <--
However, the given line is perfectly fine:
36 (define-method (send (self <actor>) msg data)
37 (mailbox-send! (slot-value self 'private-mailbox) (cons msg data)))
And I see no way that the (slot-value self 'private-mailbox) is different
from its original value:
(define-class <actor> () ((private-mailbox (make-mailbox))
(private-continue #t)))
Indeed, this is a "virtual" class (never instantiated directly but supposed
to be inherited) and the child classes never access or overwrite private-*
attributes (that why they got this prefix).
Here it appears to be the one-shot slot from the scheduler class that
correspond to this #f but I got the same bug with different actors and
different slots from the corresponding classes.
I was then wondering if I got something wrong or if there is a deeper bug
in the combo srfi-18/coops/mailbox.
If you want to have a look at the complete code you can find it at
https://github.com/Lattay/chicken-meta-rpc. You may want to look at
src/main/actor.scm (definition of the actor base class) or to
src/main/server.scm (definitions of the actual actors).
If you want to try it you may run `make test`. Dependencies are matchable,
mailbox, srfi 18 and 69 and coops.
Hoping someone could help, thank you for reading so far.
PS: I don't ask for a code review (do it if you feels like it though) since
it is not a fun thing to do but I want to check if this bug ring a bell for
some of you.
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