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Re: question about atomics

From: joakim
Subject: Re: question about atomics
Date: Fri, 26 May 2017 13:22:50 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

Chris Vine <address@hidden> writes:

> On Fri, 26 May 2017 12:37:47 +0200
> address@hidden wrote:
>> Hello,
>> I'm making a simple program that processes a lot of mail in separate
>> guile threads.
>> I would like a counter of how many messages have been processed so I
>> made an attempt with atomics.
>> first:
>>     (define *msgcount* (make-atomic-box 0))
>> and later:
>>     (atomic-box-swap! *msgcount* (+ 1 (atomic-box-ref *msgcount*)))
>> This of course doesn't work very well, and I didnt expect it to
>> either. (usually the count is low by a couple of hundred messages)
>> So basically, how do I get something similar to the swap! function in
>> clojure? Did I miss something in the documentation for guiles atomics?
>> I think I expected to be able to do the following:
>>     (atomic-box-swap! *msgcount* (lambda (atom) (+ 1 (atomic-box-ref
>> atom))))
> That won't work.  You have to use atomic-box-compare-and-swap!, in order
> to detect interleaving by other threads.  For more on this, google
> "compare and swap".


Joakim Verona

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