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bug#21887: 'monitor' form broken
From: |
Andy Wingo |
Subject: |
bug#21887: 'monitor' form broken |
Date: |
Fri, 24 Jun 2016 18:04:06 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
Hi Taylan,
On Thu 12 Nov 2015 16:29, address@hidden (Taylan Ulrich "Bayırlı/Kammer")
writes:
> 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?
You're totally right on all points. Please do prepare a patch :) I
wish we could do something faster for the "embedded" mutex but
correctness should come first.
Cheers,
Andy
- bug#21887: 'monitor' form broken,
Andy Wingo <=