Boost C++ Libraries: Ticket #7767: lockfree queue allocation problem

status changed; resolution set

timblechmann — Wed, 05 Dec 2012 09:54:23 GMT

status new → closed
resolution → invalid

not a bug: you have not configured the queue to have a capacity that is specified at compile time, so you should not use the default constructor. there is a run-time assertion, but unfortunately that fires after the memory pool is constructed with -1, which is a bit confusing. let me see, if i can improve that a bit ...

pn.suzuki.kojiro@… — Wed, 05 Dec 2012 10:36:53 GMT

Why don't you split implementation by have_capacity?

timblechmann — Wed, 05 Dec 2012 10:45:34 GMT

possible, but increases the complexity of the code as one would need an additional abstraction layer.

pn.suzuki.kojiro@… — Wed, 05 Dec 2012 15:03:57 GMT

I don't understand yet, why can't I use the default constructor in this case?
I thought that the default constructor should constructs empty queue with empty pool.

        pool(node_allocator(), has_capacity ? capacity : 0)

Does this code have a problem?

timblechmann — Wed, 05 Dec 2012 15:07:27 GMT

if you don't specify a capacity, internal nodes have to be allocated during push() or pop() ... since memory allocation is not lock-free the data-structure is not lock-free anymore ...

Wed, 05 Dec 2012 15:20:52 GMT

Thank you for your answers, I understand it now.

I have an idea.
If you use the the previous code, and leave the assertion,
it generates assertion without trying to allocate huge elements.

    queue(void):
        head_(tagged_node_handle(0, 0)),
        tail_(tagged_node_handle(0, 0)),
        pool(node_allocator(), has_capacity ? capacity : 0) // add this
    {
        BOOST_ASSERT(has_capacity); // and leave this
        initialize();
    }