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From: "Alex R. Mosteo" <devnull@mailinator.com>
Newsgroups: comp.lang.ada
Subject: Re: Problem with -gnatt
Date: Wed, 20 Oct 2004 09:59:43 +0200
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Date: 2004-10-20T09:59:43+02:00
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Simon Wright wrote:
> "Alex R. Mosteo" <devnull@mailinator.com> writes:
> 
> 
>>It isn't that contradictory? If locking is costly in a protected
>>object, using it for very frequent, very short actions seems
>>pointless. It indeed will suggest to use it for rare, longer
>>occurrences.
> 
> 
> I suppose you need to time it. There's an (x86) hi-res Time package
> inthe Booch Components (BC.Support.High_Resolution_Time, see
> http://www.pushface.org/components/bc).
> 
> For what it's worth, a mutex implemented using a protected type took
> about 20 us on a 400 MHz PowerPC under VxWorks ...
> 
> 
>>What's a spinlock?
> 
> 
> I think it means to loop until a bit becomes clear, then set it (using
> an indivisible test-and-set instruction). Doesn't work if you only
> have one CPU of course; but if it does work, and the protected regions
> are short (a few tens of instructions, depending), will be quicker
> than calling some OS sleep() operation.

Didn't know that english term for this. Thanks for the explanation. This 
is indeed a compelling argument, at least for multiprocessor machines.