[usocket-devel] Problem with :ready-only

[Chun Tian (binghe)]

Hi, Daniel

I'm very sorry for the late response for your multiple posts on the :READY-ONLY keyword argument of WAIT-FOR-INPUT.

The short answer for you will be: always use (:READY-ONLY T), and ...

here is an formal answer from the original designer of WAIT-FOR-INPUT, Erik Huelsmann:

"""
Without the READ-ONLY arg, WAIT-FOR-INPUT will return all sockets in
the original list you passed it. This prevents a new list from being
consed up. Some users of USOCKET were reluctant to use it if it
wouldn't behave that way, expecting it to cost significant performance
to do the associated garbage collection.

Without the READ-ONLY arg, you need to check the socket STATE slot for
the values documented in usocket.lisp in the usocket class:

(state
   :initform nil
   :accessor state
   :documentation "Per-socket return value for the `wait-for-input' function.

The value stored in this slot can be any of
NIL          - not ready
:READ        - ready to read
:READ-WRITE  - ready to read and write
:WRITE       - ready to write

The last two remain unused in the current version.
")
"""

In my opinion, this design is reasonable: for performance critical USOCKET applications, programmers should use (:READY-ONLY NIL), the default option, and check the status of each usocket in the waiting list, this prevents unnecessary runtime consing. For simple use, (:READY-ONLY T) is very convenient, you can just found which usocket is readable just from the return value (as a list) of WAIT-FOT-INPUT.

I hope this mail could solve your confusion.

Regards,

Chun Tian (binghe)

在 2010-5-4，06:05， Daniel Weinreb 写道：

> Hi. I just tried out the latest usocket.  It's not working
> properly for me, because wait-for-input returns true
> even when there isn't any input.
> 
> If I change the default value of the :ready-only argument to
> wait-for-input to t instead of nil, that fixes the problem.
> 
> I don't even understand why this argument
> exists; no caller seems to pass it at all!  What's going
> on here?
> 
> Thanks.
> 
> -- Dan
> 
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