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From: Alexander Terekhov <terekhov@web.de>
Newsgroups: comp.programming.threads
Subject: Re: usage of vyukov's mpsc queue
Date: Wed, 21 Sep 2011 19:33:42 +0200
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Dmitriy Vyukov wrote:
> 
> Since you are doing signaling (SetEvent) after each push, I think you
> don't need anything special for it to work.
> However of course you need correct memory fences in the queue
> algorithm itself, that is I think as follows:
> 
> void mpscq_push(mpscq_t* self, mpscq_node_t* n)
> {
>     n->next = 0;
>     mpscq_node_t* prev = XCHG(&self->head, n); // ACQUIRE_RELEASE

"// ACQUIRE" (without _RELEASE) is sufficient here.

But XCHG(...) can be totally relaxed with respect to memory barriers if
implemented as load-reserve/store-conditional or CAS loop (making
subsequent stores control-dependent).

X86 aside, try to unfold XCHG() using load-reserve/store-conditional or
CAS loop.

>     prev->next = n; // RELEASE

Yes.

> }
> 
> mpscq_node_t* mpscq_pop(mpscq_t* self)
> {
>     mpscq_node_t* tail = self->tail;
>     mpscq_node_t* next = tail->next; // ACQUIRE

Yes.

regards,
alexander.