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   |

<delay/preempted>

yet to increment seq   

                                   |    pos = 1

   |   seq = 0

   | dif = -1

   |    enqueue fails eventhough the queue is not full 

Thank you

[Dmitry Vyukov]

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).