-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Wednesday 14 May 2008 08:28 am, Anthony Williams wrote:
"vicente.botet" <vicente.botet@wanadoo.fr> writes:
Why you don't want to provide completion callbacks? Have you another proposal for completion callbacks?
I don't like them because you're chaining work onto the thread that sets the future value, and that strikes me as dangerous.
Maybe you could open the interface and return the last callback setting. This will result in a chain of responsabilities and the client must be aware of that with thow potential problems: growing stack and clients forgetting its responsabilities.
I really don't see the need for multiple wait callbacks.
To add my 2 cents: in libpoet, I allow multiple completion callbacks by providing poet::future::connect_update() which takes a slot (from thread_safe_signals). A completion callback allowed me to solve the "wait for multiple futures" problem which arose in my scheduler classes (which contain a queue of method requests, each of which must wait for a set of input futures before in can be executed). The completion callback notifies a condition variable which the scheduler thread is waiting on so it can wake up and see if any method requests have become ready. I chose signals/slots over a simple callback because I find simple callbacks unbearably primitive (no multiple callbacks, no automatic connection management). I may be more enthusiastic about using signal/slots than most however. As was mentioned earlier, It is possible to tack on a signal to a simple callback. You could bundle each future with a signal and make the callback just invoke the signal. However, that requires every future to have its own signal. By integrating the signals/slots into the future library, the future and all its copies can accept slots and forward them to a single signal which is invoked when their promise is fulfilled or reneged. If there are no completion callbacks, I regard at least the ability to wait on an arbitrary number of futures simultaneously as essential. Something that provides functionality analagous to POSIX select() on a set of file descriptors. - -- Frank -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFIKu915vihyNWuA4URAiCjAKDUNsClBfsktvFC+cShsEWe3rA62wCdEICb qkv7JM8XovbY+bn/cvpaUEw= =2KGe -----END PGP SIGNATURE-----