Johan Torp <johan.torp@gmail.com> writes:
Nice work! Let's hope we can all agree on a best interface - and get it standardized directly :)
Yes, I hope so.
Anthony Williams-3 wrote:
* Finally, I've added a set_wait_callback() function to both promise and packaged_task. This allows for lazy-futures which don't actually run the operation to generate the value until the value is needed: no threading required. It also allows for a thread pool to do task stealing if a pool thread waits for a task that's not started yet. The callbacks must be thread-safe as they are potentially called from many waiting threads simultaneously. At the moment, I've specified the callbacks as taking a non-const reference to the promise or packaged_task for which they are set, but I'm open to just making them be any callable function, and leaving it up to the user to call bind() to do that.
If you haven't, please read my concerns about direct callbacks in http://www.nabble.com/Review-Request%3A-future-library-%28Gaskill-version%29...
I have read your comments. My primary reason for including this came from thread pools: if you know that the current thread (from the pool) is blocked on a future related to a task in the pool, you can move it up the queue, or maybe even invoke on the blocked thread. Braddock suggested lazy futures, and I think that's also an important use case. For one thing, it shows that futures are useful without thread pools: you can use them in single-threaded code.
Anthony Williams-3 wrote:
I've left the wait operations as wait() and timed_wait(), but I've had a suggestion to use wait()/wait_for()/wait_until(), which I'm actively considering.
I like timed_wait because that's the same name as in condition_variable. wait_until could be confusing - one might think the thread will wait until the specified time regardless of the future is set or not. time_limited_wait or wait_max_time are further alternatives.
This was alongside a suggestion that we change the names for condition_variable waits. The important part was the separation of timed_wait(duration) vs timed_wait(absolute_time) with distinct names, so it was clear which you were calling, and you wouldn't accidentally pass a duration when you meant a fixed time point. We could go for timed_wait_for() and timed_wait_until(), but they strike me as rather long-winded. Maybe that's a good thing ;-) Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL