On 23 July 2010 14:08, Tim Blechmann <tim@klingt.org> wrote:
hi christian,
Hi Tim,
Fifo: "The fifo class provides a multi-writer/multi-reader fifo, enqueueing and dequeueing is lockfree, construction/destruction has to be synchronized"
What does it mean that construction/destruction has to be synchronized? Both these functions can only be called once.
one shouldn't try to en/dequeue from one thread, while another thread is running the constructor/destuctor. maybe it should formulated in a better way ...
Operating on a deleted object is always undefined behaviour. I think it's not related to lockfree datastructures.
bool enqueue(T const & t); Shouldn't this function throw an exception if t cannot be enqueued?
i would prefer not to throw an exception! if a constant-size freelist is used, the enqueue operation may fail, although no `error' occurred. i prefer this interface
If memory for the operation cannot be obtained, I believe common practice is to throw an exception. IMO, it does not matter if a fixed size pool is exhausted or the global heap, since the effect is the same -> a no op. With current interface I'd need to always check return value for every enqueue for out of memory conditions, something I don't need to do with any other container.
bool empty(void) //warning Not thread-safe I think this function should be removed from public interface if it cannot be implemented in a thread safe manner.
i would prefer to keep it, but warn about the thread safety. i am also thinking about adding thread-unsafe version of enqueue/dequeue/push/pop, since they can be implemented in a more efficient way than the thread-safe versions. one can think of a use case, that one thread fills a fifo/queue and then notifies consumer threads ...
Would if suffice to add another constructor for that? template<class Iterator> fifo(Iterator first, Iterator last)
Then you can have an optimized way of populating the lockfree container,without adding unsafe member functions. Something like this comes to mind: vector<int> values; shared_ptr<fifo<int>> work(new fifo<int>(values.begin(), values.end())); for(int i = 0; i < N_THREADS; ++i) start_job(work); / Christian