<div class="gmail_quote">On Sat, Oct 24, 2009 at 8:06 AM, Nadeem Abdul Hamid <<a href="mailto:nadeem@acm.org" target="_blank">nadeem@acm.org</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div>On Fri, Oct 23, 2009 at 9:35 PM, Nadeem Abdul Hamid <<a href="mailto:nadeem@acm.org" target="_blank">nadeem@acm.org</a>> wrote: > > The delay causes the code to "hang" for about 5 to 10 seconds before > it the read comes through. An interval of 5 causes a much longer > "hang". And as YC suggested, the CPU usage is max-ed out during that > period... > </div>Sorry, this was dumb. It delays exactly as expected. I've been working on this too long... </blockquote></div> Nadeem - to reduce the CPU usage you can use sync or the blocking variety of the read-* functions, so that you are not melting your computer waiting for the bytes to come through. Looking at your function's logic it doesn't appear you need the non-blocking methods, and the logic appears very similar to read-bytes, but it returns a list of bytes instead of a byte-string. So something like the below should work: (define (read-bytes/list num in) (bytes->list (read-bytes num in))) read-bytes will hang unless it has captured enough bytes or encounter an EOF. If you need the function to return before encountering EOF but doesn't hang forever - you can use other mechanisms, such as installing a max timeout: (define (read-bytes/list/timeout num in timeout) (define (helper alarm acc count) (let ((evt (sync alarm in))) (if (eq? alarm evt) (reverse acc) (let ((b (read-byte in))) (cond ((eof-object? b) (if (null? acc) b (reverse acc))) ((= (add1 count) num) (reverse (cons b acc))) (else (helper alarm (cons b acc) (add1 count)))))))) (helper (alarm-evt (+ (current-inexact-milliseconds) (* 1000 timeout))) '() 0)) In any event, it's likely that the issue lies at the port level if your simulation that provides a deterministic flow of bytes works correctly even when the cpu is maxed out. You might have better luck to investigate the port to make sure the data is flowing through. HTH, yc