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    SubjectRe: recursive spinlocks. Shoot.
    On Mon, 19 May 2003, Peter T. Breuer wrote:

    > No. This is not true. Imagine two threads, timed as follows ...
    >
    > .
    > .
    > .
    > .
    > if ((snl)->uniq == current) {
    > atomic_inc(&(snl)->count); .
    > } else { .
    > spin_lock(&(snl)->lock); .
    > atomic_inc(&(snl)->count); .
    > (snl)->uniq = current; <-> if ((snl)->uniq == current) {
    > atomic_inc(&(snl)->count);
    > } else {
    > spin_lock(&(snl)->lock);
    > atomic_inc(&(snl)->count);
    > (snl)->uniq = current;
    >
    >
    > There you are. One hits the read exactly at the time the other does a
    > write. Bang.

    So, what's bang for you ? The second task (the one that reads "uniq")
    will either see "uniq" as NULL or as (task1)->current. And it'll go
    acquiring the lock, as expected. Check it again ...




    - Davide

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