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Viewing changes to src/lock_xt.cc

  • Committer: Paul McCullagh
  • Date: 2010-05-03 12:43:05 UTC
  • mfrom: (831.2.21 1.5-trunk)
  • Revision ID: paul.mccullagh@primebase.org-20100503124305-ifpcfm7234cx4371
Merged with 1.5 trunk

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Lines of Context:
src/lock_xt.cc
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        sxs->sxs_locker = thd_id;
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#endif
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        /* Wait for all the reader to wait! */
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        while (sxs->sxs_wait_count < sxs->sxs_rlock_count)
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                xt_yield();
 
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        /* Wait for all the readers to wait! */
 
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        while (sxs->sxs_wait_count < sxs->sxs_rlock_count) {
 
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                sxs->sxs_xwaiter = 1;
 
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                xt_yield(); //*
 
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                /* This should not be required, because there is only one thread
 
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                 * accessing this value. However, the lock fails if this
 
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                 * is not done with an atomic op.
 
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                 *
 
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                 * This is because threads on other processors have the
 
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                 * value in processor cache. So they do not
 
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                 * notice that the value has been set to zero.
 
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                 * They think it is still 1 and march through
 
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                 * the barrier (sxs->sxs_xwaiter < sxs->sxs_xlocked) below.
 
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                 *
 
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                 * In the meantime, this X locker has gone on thinking
 
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                 * all is OK.
 
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                 */
 
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                xt_atomic_tas2(&sxs->sxs_xwaiter, 0);
 
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        }
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#ifdef XT_THREAD_LOCK_INFO
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        xt_thread_lock_info_add_owner(&sxs->sxs_lock_info);
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{
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        xt_atomic_inc2(&sxs->sxs_rlock_count);
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        /* Check if there could be an X locker: */
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        if (sxs->sxs_xlocked) {
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                /* I am waiting... */
 
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        /* Wait as long as the locker is not waiting: */
 
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        while (sxs->sxs_xwaiter < sxs->sxs_xlocked) {
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                xt_atomic_inc2(&sxs->sxs_wait_count);
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                while (sxs->sxs_xlocked)
 
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                while (sxs->sxs_xwaiter < sxs->sxs_xlocked) {
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                        xt_yield();
 
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                }
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                xt_atomic_dec2(&sxs->sxs_wait_count);
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        }
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