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To: Andre Oppermann <andre@freebsd.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 03 Jan 2008 01:21:30 +0100."
	<477C2A8A.8090604@freebsd.org> 
Date: Thu, 03 Jan 2008 00:26:06 +0000
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Cc: Attilio Rao <attilio@freebsd.org>, arch@freebsd.org,
	Robert Watson <rwatson@freebsd.org>, freebsd-arch@freebsd.org
Subject: Re: New "timeout" api, to replace callout 
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In message <477C2A8A.8090604@freebsd.org>, Andre Oppermann writes:

>>>>> I fear we have to go for the latter.  Getting a non-sleeping callout
>>>>> drain seems to be non-trivial.
>>>> There is a crucial difference between "non-sleeping" and "not sleeping
>>>> on my lock" that you should be very careful about in this context.
>>>>
>>>> Which is your requirement ?
>>> Calling timeout_drain() must not sleep and not drop the lock in this
>>> context (while making any pending timeout go away forever).
>> 
>> Ok, so if the timeouts callback function is running you propose to
>> do what ?  spin until it returns ?
>
>As long as the spinning is bounded [...] I don't have a perfect solution
>handy.  That's why I try to state the requirement and hope the timeout
>gurus can work out how to do it.  ;-)

It's all Alan Turings fault :-)

You can't have that, it's that simple.

What I'm proposing is that your thread will sleep on a plain, but
unrelated mutex (internal to the timeout code) until the function
comes back.

Based on your description above, you won't be able to tell the
any difference between this and what you wish for.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.