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Load the initial tail non-atomically in ponyint_mpmcq_pop #1624

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Mar 3, 2017
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Load the initial tail non-atomically in ponyint_mpmcq_pop #1624

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8 changes: 6 additions & 2 deletions src/libponyrt/sched/mpmcq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -93,10 +93,14 @@ void ponyint_mpmcq_push_single(mpmcq_t* q, void* data)
void* ponyint_mpmcq_pop(mpmcq_t* q)
{
#ifdef PLATFORM_IS_X86
PONY_ABA_PROTECTED(mpmcq_node_t*) cmp = bigatomic_load_explicit(&q->tail,
memory_order_relaxed);
PONY_ABA_PROTECTED(mpmcq_node_t*) cmp;
PONY_ABA_PROTECTED(mpmcq_node_t*) xchg;
mpmcq_node_t* tail;
// Load the tail non-atomically. If object and counter are out of sync, we'll
// do an additional CAS iteration which isn't less efficient than doing an
// atomic initial load.
cmp.object = q->tail.object;
cmp.counter = q->tail.counter;
#else
mpmcq_node_t* tail = atomic_load_explicit(&q->tail, memory_order_relaxed);
#endif
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