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streamline mutex unlock to remove a useless branch, use a_store to unlock

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this roughly halves the cost of pthread_mutex_unlock, at least for
non-robust, normal-type mutexes.

the a_store change is in preparation for future support of archs which
require a memory barrier or special atomic store operation, and also
should prevent the possibility of the compiler misordering writes.
This commit is contained in:
Rich Felker
2011-03-30 09:06:00 -04:00
parent 124b4ebc8a
commit 02084109f0
1 changed files with 6 additions and 2 deletions
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src/thread/pthread_mutex_unlock.c
+6 -2
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@@ -14,11 +14,15 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
self->robust_list.pending = &m->_m_next; self->robust_list.pending = &m->_m_next;
*(void **)m->_m_prev = m->_m_next; *(void **)m->_m_prev = m->_m_next;
if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev; if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev;
a_store(&m->_m_lock, 0);
self->robust_list.pending = 0;
} else {
a_store(&m->_m_lock, 0);
} }
} else {
a_store(&m->_m_lock, 0);
} }
m->_m_lock = 0;
if (m->_m_waiters) __wake(&m->_m_lock, 1, 0); if (m->_m_waiters) __wake(&m->_m_lock, 1, 0);
if (m->_m_type >= 4) self->robust_list.pending = 0;
return 0; return 0;
} }