Thanks for tracking this down! In case you mean a channel in the sense of `make-channel', I recommend a semaphore, instead, since a semaphore is the lightest-weight synchronization construct.
At Fri, 03 May 2013 11:45:38 -0400, Vincent St-Amour wrote: > Sam, Asumu and I found and fixed the bug. Here's the problem in a > nutshell. > > This is the implementation of `delay/thread' from racket/promise. > > (define (delay/thread thunk) > (let () > (define (run) > (call-with-exception-handler > (lambda (e) (pset! p (make-reraise e)) (kill-thread > (current-thread))) > (lambda () (pset! p (call-with-values thunk list))))) > (define p > (make-promise/thread > (make-running-thread > (object-name thunk) > (thread run)))) > p)) > > `run' depends on `p', and vice versa. The `run' thread may start > executing *before* `p' is actually defined. This causes `pset!' (which > is just promise mutation) to mutate `#<undefined>', which raises an > exception[1]. The exception handler then calls `pset!' again, which > raises an exception, and kills the thread without setting the promise's > value. > > Our solution is to have `run' block on a channel until `p' is fully > initialized. I'll push the fix. > > Vincent > > > [1] Actually, since `pset!' uses `unsafe-struct-set!', there is no > actual exception. The thread gets killed some other way. > > > At Thu, 2 May 2013 22:27:14 -0400, > Asumu Takikawa wrote: > > > > On 2013-05-02 22:14:44 -0400, Asumu Takikawa wrote: > > > This produces a promise error on every third or fifth run or so for me. > > > Commenting out the #:when line makes it work, very oddly. > > > > Tried it on another machine, the #:when line didn't matter there. Also, > > I can reproduce this more reliably on a machine with fewer cores. > > > > Cheers, > > Asumu > > _________________________ > > Racket Developers list: > > http://lists.racket-lang.org/dev > _________________________ > Racket Developers list: > http://lists.racket-lang.org/dev _________________________ Racket Developers list: http://lists.racket-lang.org/dev
