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    SubjectRe: "upping" a semaphore from interrupt context?
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    On Saturday 23 June 2007, Robert P. J. Day wrote:
    > On Fri, 22 Jun 2007, Arnd Bergmann wrote:
    > >
    > > yes, but you should not. The use of semaphores is not recommended
    > > for new code, it should be replaced with either a mutex or a
    > > completion.
    >
    > can you clarify this?  it sounds like you're saying that the current
    > implementation of semaphores is entirely superfluous.  but surely it
    > isn't possible to replace all semaphores with either mutexes or
    > completions, is it?

    No, not all of them, but the vast majority. There are multiple
    differences, the most important one being the 'counting' in
    semaphores. You can e.g. define a semaphore that can be held
    by N users at the same time, but not more. In a mutex, N is
    by definition 1, so only one thread can hold a mutex.

    There are other subtle differences in the implementation, e.g.
    you cannot mutex_trylock at interrupt time.

    Arnd <><
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