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Re: packaging Bootstrap for Cuirass' web interface
From: |
Ludovic Courtès |
Subject: |
Re: packaging Bootstrap for Cuirass' web interface |
Date: |
Fri, 27 Jul 2018 10:50:47 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Hi Clément!
Clément Lassieur <address@hidden> skribis:
> The bug is here:
>
> (define (make-critical-section . args)
> "Return a channel used to implement a critical section. That channel can
> then be passed to 'join-critical-section', which will ensure sequential
> ordering. ARGS are the arguments of the critical section.
>
> Critical sections are implemented by passing the procedure to execute to a
> dedicated fiber."
> (let ((channel (make-channel)))
> (spawn-fiber
> (lambda ()
> (let loop ()
> (match (get-message channel)
> ((? procedure? proc)
> (put-message channel (apply proc args))))
> (loop))))
> channel))
>
> (define (call-with-critical-section channel proc)
> "Call PROC in the critical section corresponding to CHANNEL. Return the
> result of PROC."
> (put-message channel proc)
> (get-message channel))
>
>
> Say I have 2 concurrent fibers (F1 and F2) wanting to serialize
> messages through the critical section.
>
> - F1-PUT-MESSAGE puts F1-MESSAGE to CRITICAL-SECTION
> - CRITICAL-SECTION gets F1-MESSAGE, which unblocks F1-PUT-MESSAGE
> - F1-GET-MESSAGE is called and blocks
>
> - F2-PUT-MESSAGE puts F2-MESSAGE, and the only receiver available
> is... F1-GET-MESSAGE, because CRITICAL-SECTION is busy
> - F2-GET-MESSAGE is called and block
>
> - CRITICAL-SECTION is done handling F1-MESSAGE, and put
> F1-MESSAGE-MODIFIED to... F2-GET-MESSAGE.
>
> F2-MESSAGE is a procedure, whereas F1-MESSAGE-MODIFIED is a list, which
> causes the (map f F2-MESSAGE) error.
D’oh! Good catch!
> A solution could be to use two channels, in and out:
>
> (define (make-critical-section . args)
> "Return a pair of channels used to implement a critical section. It can
> then be passed to 'with-critical-section', which will ensure sequential
> ordering. ARGS are the arguments of the critical section.
>
> Critical sections are implemented by passing the procedure to execute to a
> dedicated fiber."
> (let ((channel-in (make-channel))
> (channel-out (make-channel)))
> (spawn-fiber
> (lambda ()
> (let loop ()
> (match (get-message channel-in)
> ((? procedure? proc)
> (put-message channel-out (apply proc args))))
> (loop))))
> (cons channel-in channel-out)))
>
> (define (call-with-critical-section channel proc)
> "Call PROC in the critical section corresponding to CHANNEL. Return the
> result of PROC."
> (match channel
> ((channel-out . channel-in)
> (begin
> (put-message channel-out proc)
> (get-message channel-in)))))
>
> WDYT?
Or maybe like this:
(define (make-critical-section . args)
"Return a channel used to implement a critical section. That channel can
then be passed to 'join-critical-section', which will ensure sequential
ordering. ARGS are the arguments of the critical section.
Critical sections are implemented by passing the procedure to execute to a
dedicated fiber."
(let ((channel (make-channel)))
(spawn-fiber
(lambda ()
(let loop ()
(match (get-message channel)
(((? channel? reply) . (? procedure? proc))
(put-message reply (apply proc args))))
(loop))))
channel))
(define (call-with-critical-section channel proc)
"Call PROC in the critical section corresponding to CHANNEL. Return the
result of PROC."
(let ((reply (make-channel)))
(put-message channel (cons reply proc))
(get-message reply)))
That makes it clear that the reply channel is used only by the calling
fiber.
WDYT?
Thanks for debugging this!
Ludo’.
- RE: packaging Bootstrap for Cuirass' web interface, (continued)
- RE: packaging Bootstrap for Cuirass' web interface, Tatiana Sholokhova, 2018/07/24
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/24
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/25
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/25
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/25
- Re: packaging Bootstrap for Cuirass' web interface, Gábor Boskovits, 2018/07/25
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/25
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/26
- Re: packaging Bootstrap for Cuirass' web interface, Ludovic Courtès, 2018/07/26
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/26
- Re: packaging Bootstrap for Cuirass' web interface,
Ludovic Courtès <=
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/27
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/27
- Re: packaging Bootstrap for Cuirass' web interface, Ludovic Courtès, 2018/07/29
- Re: packaging Bootstrap for Cuirass' web interface, Ludovic Courtès, 2018/07/26
- Re: packaging Bootstrap for Cuirass' web interface, Clément Lassieur, 2018/07/29
- Re: packaging Bootstrap for Cuirass' web interface, Ludovic Courtès, 2018/07/26
Re: packaging Bootstrap for Cuirass' web interface, Björn Höfling, 2018/07/23