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DragonFly kernel List (threaded) for 2010-05
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Re: Soft token staleness question

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 27 May 2010 12:40:43 -0700 (PDT)

:Why is lwkt_token_is_stale if 0-ed out?
:If I understand the motivation behind tokens, higher level code can take it
:an call lower level code which can block. But without the ability to check
:staleness, how you know if lower level code blocked and allowed your
:assumptions made under the token earlier to be invalidated?
:-- vs

    It's hard to say how useful a staleness indicator is because using
    such an indicator means having more complex, harder-to-debug code,
    verses simply coding things to assume the lock was temporarily
    broken whenever something might block.

    I think there are a few cases where it would be useful, particularly
    in the VM subsystem when it eventually gets converted over to MPSAFE
    code.  It would not be useful for most of the existing use cases.

					Matthew Dillon 

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