Consecutive Lwt_react.E.next calls on an event return the same occurrence.

[ocsigen]

Consecutive Lwt_react.E.next calls on an event return the same occurrence.

Well Lwt.wakeup_later is the same as Lwt.wakeup if not called inside another Lwt.wakeup or Lwt.wakeup_later.

Note that calling Lwt_react.E.next in a loop is a very bad idea. I didn't realized it at first when I wrote it but it can destroy performances.

[mfp]

On Fri, May 02, 2014 at 01:19:48AM -0700, Jérémie Dimino wrote:

Well Lwt.wakeup_later is the same as Lwt.wakeup if not called inside another Lwt.wakeup or Lwt.wakeup_later.

Note that calling Lwt_react.E.next in a loop is a very bad idea. I didn't realized it at first when I wrote it but it can destroy performances.

Could you expand a bit on that? Is it because of the use of React.E.once?

On top of that and on second thought, Lwt_react.E.next is also treacherous
because it looks like Lwt_stream.next and thus invites to use it in a loop to
get all the occurrences, but you'll lose some if there are context switches in
the middle.

So it is probably better to leave it as is and instead add some words of
warning in the docs along with a suggestion to use Lwt_react.E.to_stream +
Lwt_stream.next instead.

Mauricio Fernández

Could you expand a bit on that? Is it because of the use of React.E.once?

Yes. Some weak array in react might grow quite a lot. I observed this a long time ago in a gtk program using it. The interface was getting slower and slower because of it.

On top of that and on second thought, Lwt_react.E.next is also treacherous
because it looks like Lwt_stream.next and thus invites to use it in a loop to
get all the occurrences, but you'll lose some if there are context switches in
the middle.

Definitely

So it is probably better to leave it as is and instead add some words of
warning in the docs along with a suggestion to use Lwt_react.E.to_stream +
Lwt_stream.next instead.

fine by me

[rneswold]

So it is probably better to leave it as is and instead add some words of warning in the docs along with a suggestion to use Lwt_react.E.to_stream + Lwt_stream.next instead.

Does Lwt_react.E.to_stream guarantee it won't drop events if there are context switches? If so, the docs should reflect that, too.