--- Begin Message ---
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Subject: |
'monitor' form broken |
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Date: |
Thu, 12 Nov 2015 16:29:30 +0100 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
It seems that the 'monitor' form is currently a no-op. The form
(par-for-each (lambda (x)
(monitor
(foo)))
xs)
should be functionally equivalent to
(let ((mutex (make-mutex)))
(par-for-each (lambda (x)
(with-mutex mutex
(foo)))
xs))
but currently becomes
(par-for-each (lambda (x)
(let ((mutex (make-mutex)))
(with-mutex mutex
(foo))))
xs)
which is ineffective.
I don't know what's the best way to fix this. The simplest thing that
comes to my mind is something along the lines of:
(define-syntax monitor
(lambda (stx)
(syntax-case stx ()
((_ body body* ...)
(let ((uuid (generate-uuid)))
#`(with-mutex (mutex-with-uuid #,uuid)
body body* ...))))))
where mutex-with-uuid looks it up from a hash table at run-time and
instantiates it when it doesn't exist, this operation also being
synchronized across threads, like:
(define mutex-table (make-hash-table))
(define mutex-table-mutex (make-mutex))
(define (mutex-with-uuid uuid)
(with-mutex mutex-table-mutex
(or (hash-ref mutex-table uuid)
(let ((mutex (make-mutex)))
(hash-set! mutex-table uuid mutex)
mutex))))
If that looks OK, I can try to make a proper patch from it. I'm not
sure what I'd use in place of `generate-uuid' though. Would `gensym' be
good enough?
Shameless advertisement: with SRFI-126, the (or (hash-ref ...) ...) bit
would have been just:
(hashtable-intern! mutex-table uuid make-mutex)
It's borrowed from MIT/GNU Scheme. Seems pretty useful.
Taylan
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