2015-08-25 21:22 GMT+08:00 Niall Douglas <s_sourceforge@nedprod.com>:
2. The reason why it's shared_ptr<handle> not handle * is precisely because of how to manage lifetime over unknown continuations. If the user writes:
future<> oh=async_file("niall.txt"); future<> reads[100]; for(size_t n=0; n<100; n++) reads[n]=async_read(oh, buffers[n], 10, n*4096);
So this schedules niall.txt to be opened, and then adds 100 continuations onto that file open each of which schedules the read of 10 bytes from a 4Kb multiple. All those 100 continuations occur in *parallel*, and could complete in *any* order.
So how do you keep the handle to the niall.txt file around until the last continuation using that file has completed which is at some, unknown point in the future? The natural fit is shared_ptr. It's exactly what it was designed for.
Does this make sense?
I think it's an design issue, I wonder if it's possible to design the API around the ASIO model, e.g. ``` afio::file file(io); // move-only await file.async_open("niall.txt"); future<size_t> reads[100]; for(size_t n=0; n<100; n++) reads[n] = file.async_read(buffers[n], 10, n*4096); ``` Drop the dependency based API, since the forthcoming coroutine should solve it for you elegantly. This way, you don't need shared semantic for future<>, just like how we used to do with ASIO.