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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 12:19:49 +0200
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Ephi Sinowitz wrote:
> 
> Hi,
> I implemented the queue http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-m...
> with a signaling mechanism for the consumer.
> Do I need to ensure visibility somehow before setting the event since
> I'm not spinning in the consumer? How?
> Producers:
> ----------------
>     vyukov_queue.push(item);
>     SetEvent(m_queueEvent);
> Consumer:
> ---------------
>     for(;;)
>     {
>         WaitForSingleObject(m_queueEvent, INFINITE);
>         while (void* item = vyukov_queue.pop())
>         {
>             // do work
>         }
>     }
> For reference here is the push()
> void MPSC_Queue::push(void* item)
> {
>     item->next = NULL;
>     void* old_head = InterlockedExchangePointer((void *volatile
> *)&m_head, item);
>     // BLOCK POINT
>     old_head->next = item;  // Do I need to ensure this is visible to
> the consumer thread?
> }

Yes, you need to make old_head->next = item store atomic-release store.

Consumer's m_tail->next load must be atomic-acquire load.

Producer's RMW can be totally relaxed with respect to memory barriers.

regards,
alexander.