DragonFly kernel List (threaded) for 2004-04
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re: serializing token
Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx> wrote in
news:200404240602.i3O620uD010997@xxxxxxxxxxxxxxxxxxxx:
> 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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