Sounds good, I'll use a semaphore. Vincent
At Fri, 3 May 2013 09:58:25 -0600, Matthew Flatt wrote: > > 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
