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Date:      Sun, 14 Feb 1999 16:31:27 -0800
From:      David Greenman <dg@root.com>
To:        "Masahiro Ariga" <mariga@cd.mbn.or.jp>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Please untangle my brain. 
Message-ID:  <199902150031.QAA14048@implode.root.com>
In-Reply-To: Your message of "Mon, 15 Feb 1999 03:12:27 +0900." <000301be5845$ba8022e0$064ca8c0@gateway> 

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>And made it run,expecting the output should be as follows,
>This is child! num=0
>This is parent! num=0
>This is child! num=1
>This is parent! num=1
>and so on,but instead the actual output was as follows.
>
>This is child! num=0
>This is child! num=1
>This is child! num=2
>This is child! num=3
>This is child! num=4
>This is parent! num=0
>This is parent! num=1
>This is parent! num=2
>This is parent! num=3
>This is parent! num=4
>
>I am puzzeled.Why in the world this could happen,what was going in
>UNIX?Please someone untangle my mystified brain.

   As in most multi-tasking systems, FreeBSD processes usually run for a
quantum (or "time slice") before switching to another process. The length
of the quantum in FreeBSD is 100ms. How long a process runs when there
are other running processes is more complicated than just the quantum,
however, since there is also a sophisticated priority queueing mechanism
that biases the running of 'interactive' processes over compute bound
processes. It's not my intention to get deeply into the details here of
how it all works - just to explain why the output was as you've observed
it above.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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