[slime-devel] What does swank do with streams?

[Helmut Eller]

* mikel evins [2009-06-02 17:31+0200] writes:

> Doubtless this is because we don't properly understand what swank is  
> doing with the streams. I frankly don't know how to frame an  
> intelligent question on this subject, because I don't know enough  
> about what swank is trying to accomplish and how it's going about it.  

Basically SWANK installs a custom stream in *STANDARD-OUTPUT*
and that stream forwards any output to the slime-repl Emacs buffer.
We usually do this with dynamic bindings like

      (let ((*standard-output* <custom-stream>)
            (*standard-input* <custom-stream>)
            (*debug-io* <custom-stream>)
            (*query-io* <custom-stream>)
            (*terminal-io* <custom-stream>))
           ...)

before evaluating code that (potentially) generates output.  We actually
use PROGV but that's a minor detail.

A more problematic feature is "global IO redirection".  This installs
our stream as the truly global value for *STANDARD-OUTPUT* etc.  and
also as the default value for new threads.  The reason to do such a
global thing at all is the desire to redirect the output of threads
created by a HTTP server, or generally threads that are not created by
us.  Global IO redirection is not enabled by default.

> So, what questions should I ask? My goal is to ensure that CCL  
> controls the standard streams in a way it can rely on, while still  
> allowing a swank server to be created and run.

With *globally-redirect-io* enabled you're probably out of luck because
we take over control.  As often in CL, this could be solved by some
convention but there is no established convention.

> If you guys would help me zero in on the right questions to ask you  
> about swank's operation, I'd appreciate it.

Maybe you could think about the HTTP server example and where debug
output of worker threads should go and how to control that.

Helmut.