Re: [boost] [lockfree] Faulty (?) static assert

Subject: Re: [boost] [lockfree] Faulty (?) static assert
From: Tim Blechmann (tim_at_[hidden])
Date: 2012-09-03 04:24:40

>>>>> which implies that 'has_capacity' is allowed to be false. From what
>>>>> I can see 'has_capacity' could be false, indeed, in particular if
>>>>> the queue is not bounded in size.
>>>>
>>>> the idea is that the default constructor is only allowed, when the
>>>> capacity is set at compile-time. otherwise the data structure won't
>>>> be completely lockfree, as creating new nodes will hit the memory
>> allocator.
>>>> so the assertion is correct, but the initialization of the pool can
>>>> be changed.
>>>
>>> Hmmm, I do not understand. If the queue is constructed with
>>> fixed_size<false> (which is the default), this assertion will _always_
>>> fire as you're not required to specify a capacity in this case.
>>
>> that's the purpose of this assertion. if the data structure is not fixed-
>> sized, you should use the explicit queue(int capacity) constructor in
>> order to populate the free-list.
> 
> I still don't understand why I shouldn't be allowed to default construct a
> queue with fixed_size<false> and without specifying a capacity. Why do I
> need to pass an initial number of nodes to the constructor in this case?

while it is technically ok to allocate a queue with an empty freelist,
this queue won't be lockfree, as the first enqueue operations will hit
the memory allocator. with this API, i'm trying to encourage users to
reserve enough space for their use cases.

tim