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    SubjectRe: [take25 1/6] kevent: Description.
    On Wed, Nov 22, 2006 at 03:46:42PM -0800, Ulrich Drepper ( wrote:
    > Evgeniy Polyakov wrote:
    > >+ int kevent_wait(int ctl_fd, unsigned int num, __u64 timeout);
    > >+
    > >+ctl_fd - file descriptor referring to the kevent queue
    > >+num - number of processed kevents
    > >+timeout - this timeout specifies number of nanoseconds to wait until
    > >there is + free space in kevent queue
    > >+
    > >+Return value:
    > >+ number of events copied into ring buffer or negative error value.
    > This is not quite sufficient. What we also need is a parameter which
    > specifies which ring buffer the code assumes is currently active. This
    > is just like the EWOULDBLOCK error in the futex. I.e., the kernel
    > doesn't move the thread on the wait list if the index has changed.
    > Otherwise asynchronous ring buffer filling is impossible. Assume this
    > thread kernel
    > get current ring buffer idx
    > front and tail pointer the same
    > add new entry to ring buffer
    > bump front pointer
    > call kevent_wait()
    > With the interface above this leads to a deadlock. The kernel delivered
    > the event and is done with it.

    Kernel does not put there a new entry, it is only done inside
    kevent_wait(). Entries are put into queue (in any context), where they can be obtained
    from only kevent_wait() or kevent_get_events().

    Evgeniy Polyakov
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      Last update: 2006-11-23 12:57    [W:0.035 / U:6.176 seconds]
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