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Use C11 atomics in pthread_once.
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@ -1,3 +1,8 @@
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2014-11-20 Torvald Riegel <triegel@redhat.com>
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* nptl/pthread_once.c (clear_once_control, __pthread_once_slow,
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__pthread_once): Use C11 atomics.
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2014-11-20 Torvald Riegel <triegel@redhat.com>
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* csu/tst-atomic.c (do_test): Add tests for C11-like atomics.
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@ -34,7 +34,7 @@ clear_once_control (void *arg)
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other threads that see this value: This function will be called if we
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get interrupted (see __pthread_once), so all we need to relay to other
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threads is the state being reset again. */
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*once_control = 0;
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atomic_store_relaxed (once_control, 0);
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lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
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}
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@ -68,20 +68,18 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
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{
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while (1)
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{
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int oldval, val, newval;
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int val, newval;
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/* We need acquire memory order for this load because if the value
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signals that initialization has finished, we need to see any
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data modifications done during initialization. */
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val = *once_control;
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atomic_read_barrier ();
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val = atomic_load_acquire (once_control);
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do
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{
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/* Check if the initialization has already been done. */
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if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0))
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return 0;
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oldval = val;
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/* We try to set the state to in-progress and having the current
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fork generation. We don't need atomic accesses for the fork
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generation because it's immutable in a particular process, and
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@ -90,18 +88,17 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
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newval = __fork_generation | __PTHREAD_ONCE_INPROGRESS;
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/* We need acquire memory order here for the same reason as for the
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load from once_control above. */
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val = atomic_compare_and_exchange_val_acq (once_control, newval,
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oldval);
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}
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while (__glibc_unlikely (val != oldval));
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while (__glibc_unlikely (!atomic_compare_exchange_weak_acquire (
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once_control, &val, newval)));
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/* Check if another thread already runs the initializer. */
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if ((oldval & __PTHREAD_ONCE_INPROGRESS) != 0)
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if ((val & __PTHREAD_ONCE_INPROGRESS) != 0)
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{
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/* Check whether the initializer execution was interrupted by a
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fork. We know that for both values, __PTHREAD_ONCE_INPROGRESS
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is set and __PTHREAD_ONCE_DONE is not. */
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if (oldval == newval)
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if (val == newval)
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{
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/* Same generation, some other thread was faster. Wait. */
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lll_futex_wait (once_control, newval, LLL_PRIVATE);
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@ -122,8 +119,7 @@ __pthread_once_slow (pthread_once_t *once_control, void (*init_routine) (void))
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/* Mark *once_control as having finished the initialization. We need
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release memory order here because we need to synchronize with other
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threads that want to use the initialized data. */
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atomic_write_barrier ();
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*once_control = __PTHREAD_ONCE_DONE;
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atomic_store_release (once_control, __PTHREAD_ONCE_DONE);
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/* Wake up all other threads. */
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lll_futex_wake (once_control, INT_MAX, LLL_PRIVATE);
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@ -138,8 +134,7 @@ __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
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{
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/* Fast path. See __pthread_once_slow. */
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int val;
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val = *once_control;
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atomic_read_barrier ();
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val = atomic_load_acquire (once_control);
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if (__glibc_likely ((val & __PTHREAD_ONCE_DONE) != 0))
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return 0;
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else
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