Shadowing special variables in threaded handlers

[Duncan Bayne]

Hi,

I'm trying to write some end to end tests for the germinal library,
which uses usockets.

What I'm trying, and failing, to do is to shadow special variables in my
tests so that test-specific configuration is scoped just to the tests in
question.

This (tidied up) REPL session with a simple repro case using just
usocket and usocket-server should give a sense of what I'm trying to
achieve:

CL-USER> (ql:quickload '(:usocket :usocket-server))
(:USOCKET :USOCKET-SERVER)
CL-USER> (defvar *foo* "original value")
*FOO*
CL-USER> (defun create-server ()
           (usocket:socket-server "0.0.0.0" 1965
                                  (lambda (stream) (write *foo* :stream stream))
                                  ()
                                  :multi-threading t
                                  :element-type 'character
                                  :in-new-thread t))
CREATE-SERVER
CL-USER> (let ((*foo* "shadowed value")) (create-server))
#<SB-THREAD:THREAD "USOCKET Server" RUNNING {10043A6933}>
#<USOCKET:STREAM-SERVER-USOCKET {10043A67D3}>

So what I'm hoping for here is for the socket server to return "shadowed
value" when a connection is opened; of course that doesn't happen,
because the handler runs in a new thread which is bereft of the let
context:

$ telnet localhost 1965
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
"original value"

I'd appreciate any assistance here ... I'm somewhat new to Common Lisp
with only a little commercial experience in it beyond hobbyist work.

I don't know whether there's a "Lisp trick" I should be using to ensure
the right context for the handler thread, or whether I need to refactor
the library in question to not rely on special variables in the handler
...

--
Duncan Bayne
+61 420 817 082 | https://duncan.bayne.id.au/

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