Re: [lock-free] regarding mpmc bounded queue

[Dmitry Vyukov]

On Sun, Oct 15, 2017 at 11:40 AM, user1990 k  wrote:
> Dear All,
>
> I was trying to understand this.
> http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
>
> Let me consider enqueue scenario [ both threads ]
>
> Thread 1 in core 0  | Thread 2 in core 0
>
> pos = 0|
> seq = 0|
> dif = 0|
> cas succeed, pos =1   |
> 
> yet to increment seq
>|pos = 1
>|   seq = 0
>| dif = -1
>|enqueue fails eventhough the queue is not full

Hi,

The seq are initialized to their indexes initially, see ctor:

for (size_t i = 0; i != buffer_size; i += 1)
  buffer_[i].sequence_.store(i, std::memory_order_relaxed);

So for pos=1 seq will be 1 (diff=0).

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[lock-free] regarding mpmc bounded queue

[user1990 k]

Dear All,

I was trying to understand this.
http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue

Let me consider enqueue scenario [ both threads ]

Thread 1 in core 0  | Thread 2 in core 0

pos = 0|
seq = 0|
dif = 0|
cas succeed, pos =1   |

yet to increment seq
   |pos = 1
   |   seq = 0
   | dif = -1
   |enqueue fails eventhough the queue is not full


Thank you

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