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    SubjectRe: Linux Driver - Select Implementation!
    Jeff Epler <> wrote:
    > What would the consequences be of a select-like call which had the semantic
    > that only one of the tasks sleeping for that resource was woken (the
    > longest-sleeping, perhaps)? (And, probably, all tasks sleeping because
    > of regular select()) To my naive mind it sounds like a way to avoid
    > the thundering herd problem. Are there unforseen pitfalls in this, or is
    > it more a matter of doing something nonstandard, or of the change requiring
    > widespread kernel changes?

    This thundering herd problem can be solved in userland, if I am not mistaken.
    From what I've read, Apache solves this problem by having a single task do the
    select(), and setting an appropriate semaphore on return. The rest of the
    tasks which would normally do a select() instead wait on this semaphore -- when
    the semaphore is available, a single task is unblocked from waiting on it.

    Charles Cazabon <>
    Any opinions expressed are just that -- my opinions.

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