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Use C11 atomics in pthread_once.

This commit is contained in:
Torvald Riegel 2014-10-21 00:34:53 +02:00
parent 1eccfecd40
commit e37c91d419
2 changed files with 14 additions and 14 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
2014-11-20 Torvald Riegel <triegel@redhat.com>
* nptl/pthread_once.c (clear_once_control, __pthread_once_slow,
__pthread_once): Use C11 atomics.
2014-11-20 Torvald Riegel <triegel@redhat.com>
* csu/tst-atomic.c (do_test): Add tests for C11-like atomics.

23
nptl/pthread_once.c
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@ -34,7 +34,7 @@ clear_once_control (void *arg)
other threads that see this value: This function will be called if we
get interrupted (see __pthread_once), so all we need to relay to other
threads is the state being reset again. */
*once_control = 0;
atomic_store_relaxed (once_control, 0);
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
}
@ -68,20 +68,18 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
{
while (1)
{
int oldval, val, newval;
int val, newval;
/* We need acquire memory order for this load because if the value
signals that initialization has finished, we need to see any
data modifications done during initialization. */
val = *once_control;
atomic_read_barrier ();
val = atomic_load_acquire (once_control);
do
{
/* Check if the initialization has already been done. */
if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0))
return 0;
oldval = val;
/* We try to set the state to in-progress and having the current
fork generation. We don't need atomic accesses for the fork
generation because it's immutable in a particular process, and
@ -90,18 +88,17 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
newval = __fork_generation | __PTHREAD_ONCE_INPROGRESS;
/* We need acquire memory order here for the same reason as for the
load from once_control above. */
val = atomic_compare_and_exchange_val_acq (once_control, newval,
oldval);
}
while (__glibc_unlikely (val != oldval));
while (__glibc_unlikely (!atomic_compare_exchange_weak_acquire (
once_control, &val, newval)));
/* Check if another thread already runs the initializer. */
if ((oldval & __PTHREAD_ONCE_INPROGRESS) != 0)
if ((val & __PTHREAD_ONCE_INPROGRESS) != 0)
{
/* Check whether the initializer execution was interrupted by a
fork. We know that for both values, __PTHREAD_ONCE_INPROGRESS
is set and __PTHREAD_ONCE_DONE is not. */
if (oldval == newval)
if (val == newval)
{
/* Same generation, some other thread was faster. Wait. */
lll_futex_wait (once_control, newval, LLL_PRIVATE);
@ -122,8 +119,7 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
/* Mark *once_control as having finished the initialization. We need
release memory order here because we need to synchronize with other
threads that want to use the initialized data. */
atomic_write_barrier ();
*once_control = __PTHREAD_ONCE_DONE;
atomic_store_release (once_control, __PTHREAD_ONCE_DONE);
/* Wake up all other threads. */
lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
@ -138,8 +134,7 @@ __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
{
/* Fast path. See __pthread_once_slow. */
int val;
val = *once_control;
atomic_read_barrier ();
val = atomic_load_acquire (once_control);
if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0))
return 0;
else