need for another mutex type/flag?

Robert Watson rwatson at
Tue Jan 27 07:10:49 PST 2009

On Sun, 25 Jan 2009, Julian Elischer wrote:

> Even purely documentary would be good but given the option, I'd like it to 
> scream when Witness is enabled and you try get another mutex....
> there are certain contexts (e.g. in most netgraph nodes) where we really 
> want the authors to only take such locks and taking more unpredictable 
> mutexes plays havoc with netgraph response times as a system as a whole, 
> since if one node blocks, teh thread doesn't get to go off and service other 
> nodes.

I thought lots of Netgraph nodes liked to do things like call m_pullup() and 
m_prepend()?  Disallowing acquiring mutexes will prevent them from doing that.

Robert N M Watson
Computer Laboratory
University of Cambridge

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