Thanks Matthew - very cool idea. I'll try to apply it to my code base and see how it works. Thanks, yc <div class="gmail_quote">On Fri, Apr 17, 2009 at 7:03 PM, Matthew Flatt <<a href="mailto:mflatt@cs.utah.edu">mflatt@cs.utah.edu</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 class="im">At Fri, 17 Apr 2009 18:33:12 -0700, YC wrote: > what are some approaches to determine where in code the thread execution (or > multiple threads) hangs? </div>Here's a function that creates a thread to watch a different thread. Every `delay' seconds, it grabs a stack trace of the thread `t': (define (watch-thread t delay) ;; create a new thread to report snapshots of t: (thread (lambda () (let loop () (sleep delay) (let ([trace (continuation-mark-set->context (continuation-marks t))]) (unless (null? trace) (for-each print-location trace) (newline))) (loop))))) Maybe something like that would help you. Here's a basic print-location function to use with watch-thread: (define (print-location i) (let ([id (car i)] [src (cdr i)]) (cond [src (printf "~a:~a~a\n" (srcloc-source src) (if (srcloc-line src) (format "~a:~a" (srcloc-line src) (srcloc-column src)) (srcloc-position src)) (if id (format ": ~a" id) ""))] [id (printf "~a\n" id)] [else (printf "???\n")]))) For example, the following shows where all the time goes when you load the implementation of the main PLT Scheme reference: (let ([watcher-t (watch-thread (current-thread) 0.1)]) (dynamic-require '(lib "scribblings/reference/reference.scrbl") #f) (kill-thread watcher-t)) This is a noisy way to monitor a thread, though. Instead of dumping each stack trace, you might just save it to check later when the thread seems to be stuck. The gprof-like profiler that Eli mentioned on plt-dev works in a similar way: <a href="http://list.cs.brown.edu/pipermail/plt-dev/2009-April/000543.html" target="_blank">http://list.cs.brown.edu/pipermail/plt-dev/2009-April/000543.html</a> </blockquote></div>