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DragonFly kernel List (threaded) for 2004-04
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re: serializing token

From: "Justin C. Sherrill" <justin@xxxxxxxxxxxxxxxxxx>
Date: 25 Apr 2004 02:48:15 GMT

Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx> wrote in

>     If you look at FreeBSD-5, you will notice that
>     FreeBSD-5 passes held mutexes down the subroutine stack quite
>     often, in order to allow some very deep procedural level to
>     temporarily release a mutex in order to switch or block or deal
>     with a deadlock.  
[trimmed for brevity] 
>     You don't have any of that mess with the token abstration but
>     there is a cost and that cost is that you lose atomicy across
>     blocking ops. 

Is this a proper analogy?  Mutexes are like additive door locks, where
having any door locked in a series of doors makes them all impassable
during the lock period.  Tokens are like a passcard, which opens a
single door out of a series, but you have to have the passcard for each
door to open them all.  Or am I getting too symbolic? 

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