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    SubjectRe: furwocks: Fast Userspace Read/Write Locks
    Rusty Russell wrote:

    > In message <20020307153228.3A6773FE06@smtp.linux.ibm.com> you write:
    >
    >>On Thursday 07 March 2002 07:50 am, Arjan van de Ven wrote:
    >>
    >>>Rusty Russell wrote:
    >>>
    >>>>This is a userspace implementation of rwlocks on top of futexes.
    >>>>
    >>>question: if rwlocks aren't actually slower in the fast path than
    >>>futexes,
    >>>would it make sense to only do the rw variant and in some userspace
    >>>layer
    >>>map "traditional" semaphores to write locks ?
    >>>Saves half the implementation and testing....
    >>>
    >>I m not in favor of that. The dominant lock will be mutexes.
    >>
    >
    > To clarify: I'd love this, but rwlocks in the kernel aren't even
    > vaguely fair. With a steady stream of overlapping readers, a writer
    > will never get the lock.
    >
    > Hope that clarifies,


    But you talk about the current implementation, don't you?
    Is there something to prevent an implementation of rwlocks in the
    kernel, where a wrlock will lock (postponed) further rdlock requests?

    I mean: the wrlocker prevents newly rdlocks to succeed and waits for the
    current rdlockers to release the lock an then gets the lock..


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