I want to use one library that works with Lwt (multipart_form_lwt) and another library that works with Async (mssql) in a project that is currently written using Lwt. I can envisage a variety of solutions: Use the lower-level API of multipart_form to get it working with Async and port the whole pr…

I’ve never used Async, but Lwt has Lwt_preemptive.run_in_main, which you could call from the Async thread presumably (with Lwt main running in a separate thread).

Another option: use the lower-level API of mssql, which is ocaml-freetds. E.g.: https://github.com/kennknowles/ocaml-freetds/blob/master/examples/dbi_example.ml

I would also consider functorizing mssql to support Async/blocking IO. From a brief look at the code I think this would be non-trivial but doable.

Functorizing is an interesting idea but I just the advice here (from Cohttp experience) was against doing so: http://rgrinberg.com/posts/abandoning-async/ However, I found an old post here that mentions the idea of forking a child process that uses the other async library. That sounds like a great…

Functorizing works well sometimes, but it will not be very appealing in this case. The library in question (ocaml-mssql?) is split into many modules and relies on a few modules from async that might not have immediate Lwt analogues. Why don’t you just the parent library ocaml-mssql is based on? Fre…

Definitely a possibility. Only problem is that I’m new to these async libraries and have no idea what is going on yet. :slight_smile:

Hint: use the Lwt_pool module to set up a connection pool. It’s pretty nicely documented.

[image] Jon_Harrop: I’m guessing I am not the first person to have faced this challenge so I’m wondering if there is a preferred solution? You might find some of the discussion here useful. [image] Best practice on mixing Async and Lwt? Ecosystem Sorry if this is a…

Yeah, you could probably make something similar to Mssql using Lwt_pool + however you spawn background threads in Lwt. I think we’d be open to making mssql work on Lwt, but it’s probably non-trivial since the library uses Sequencers and threads.

(Disclaimer: I’m not offering any solution (nor advice), just sharing some folklore.) A long time ago, @jeremiedimino and I wrote GitHub - janestreet/lwt-async: Lwt with async backend , which defines 'a Lwt.t as 'a Or_exn.t Async.Deferred.t (see here ).

Working with both Lwt and Async in the same project?

Learning

mbacarella September 15, 2021, 1:19am 9

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Working with both Lwt and Async in the same project?

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