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cheap special-case optimization for normal mutexes

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cycle-level benchmark on atom cpu showed typical pthread_mutex_lock
call dropping from ~120 cycles to ~90 cycles with this change. benefit
may vary with compiler options and version, but this optimization is
very cheap to make and should always help some.
This commit is contained in:
Rich Felker 2011-03-30 08:58:25 -04:00
commit 124b4ebc8a
1 changed files with 4 additions and 0 deletions
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4
src/thread/pthread_mutex_lock.c
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@ -3,6 +3,10 @@
int pthread_mutex_lock(pthread_mutex_t *m)
{
int r;
if (m->_m_type == PTHREAD_MUTEX_NORMAL && !a_swap(&m->_m_lock, 1))
return 0;
while ((r=pthread_mutex_trylock(m)) == EBUSY) {
if (!(r=m->_m_lock) || (r&0x40000000)) continue;
if ((m->_m_type&3) == PTHREAD_MUTEX_ERRORCHECK