# \#async **URL:** https://discuss.ocaml.org/tag/async/29.md [Latest](https://discuss.ocaml.org/latest.md) · [Categories](https://discuss.ocaml.org/categories.md) · [Tags](https://discuss.ocaml.org/tags.md) --- ## [Jane Street Libraries (base/core/async/etc) with 5.5](https://discuss.ocaml.org/t/jane-street-libraries-base-core-async-etc-with-5-5/18469)
**Author:** [@smuenzel](https://discuss.ocaml.org/u/smuenzel)\ **Replies:** 3\ **Last updated:** [October 20, 2026, 8:20am UTC](https://discuss.ocaml.org/t/jane-street-libraries-base-core-async-etc-with-5-5/18469 "2026-10-20T08:20:56Z")
(Note: much of the linked repos are modified with the the help of LLMs, so please do check the diff to the upstream version before installing. Most diffs are very small. Also, this release is not affiliated with Jane Str… --- ## [Where are the docs for core, async?](https://discuss.ocaml.org/t/where-are-the-docs-for-core-async/17783)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 5\ **Last updated:** [February 7, 2026, 10:55pm UTC](https://discuss.ocaml.org/t/where-are-the-docs-for-core-async/17783 "2026-02-07T22:55:27Z")
There are no docs on the web page any more. E.g. core v0.17.1 (latest) · OCaml Package --- ## [SSL certificates error with websockets client connecting to localhost](https://discuss.ocaml.org/t/ssl-certificates-error-with-websockets-client-connecting-to-localhost/17787)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 3\ **Last updated:** [February 7, 2026, 10:27pm UTC](https://discuss.ocaml.org/t/ssl-certificates-error-with-websockets-client-connecting-to-localhost/17787 "2026-02-07T22:27:50Z")
Hey, I am getting an error when using the cohttp\_async\_websocket package. I am connecting to localhost (monitor.ml.Error (Ssl\_error ("error:0A000086:SSL routines::certificate verify failed") src/ssl.ml:201:20) ("Cal… --- ## [Help debug ocaml async websocket echo client](https://discuss.ocaml.org/t/help-debug-ocaml-async-websocket-echo-client/17782)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 2\ **Last updated:** [February 7, 2026, 3:52am UTC](https://discuss.ocaml.org/t/help-debug-ocaml-async-websocket-echo-client/17782 "2026-02-07T03:52:08Z")
Hey, I am connecting a client to the web sockets org echo server. This is my code open Core open Async let send\_and\_receive () = let uri = Uri.of\_string "wss://echo.websocket.org" in print\_endline "connecting"; … --- ## [Sample client and server with Async websockets](https://discuss.ocaml.org/t/sample-client-and-server-with-async-websockets/17629)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 0\ **Last updated:** [December 23, 2025, 3:52pm UTC](https://discuss.ocaml.org/t/sample-client-and-server-with-async-websockets/17629 "2025-12-23T15:52:06Z")
Hey, is there a tutorial on using Async websockets? I am looking for something similar to: Quick examples - websockets 15.0.1 documentation ocaml-grpc/examples/helloworld-tutorial.md at main · dialohq/ocaml-grpc · GitH… --- ## [Can't install async 0.17.0 on macOS 15.4](https://discuss.ocaml.org/t/cant-install-async-0-17-0-on-macos-15-4/16468)
**Author:** [@anta40](https://discuss.ocaml.org/u/anta40)\ **Replies:** 9\ **Last updated:** [April 15, 2025, 3:49pm UTC](https://discuss.ocaml.org/t/cant-install-async-0-17-0-on-macos-15-4/16468 "2025-04-15T15:49:12Z")
I experienced this confusing errors when installing async === install 5 packages ∗ async v0.17.0 ∗ async\_log v0.17.0 \[required by async\] ∗ async\_unix v0.17.0 \[required by async\] ∗ core\_unix v0.17.0 \[requi… --- ## [Best practices and design patterns for supporting concurrent IO in libraries](https://discuss.ocaml.org/t/best-practices-and-design-patterns-for-supporting-concurrent-io-in-libraries/15001)
**Author:** [@zoj613](https://discuss.ocaml.org/u/zoj613)\ **Replies:** 6\ **Last updated:** [September 9, 2024, 3:34am UTC](https://discuss.ocaml.org/t/best-practices-and-design-patterns-for-supporting-concurrent-io-in-libraries/15001 "2024-09-09T03:34:39Z")
I am interested in learning about the best practices and recommended design patterns in 2024 for supporting concurrent IO in libraries. I noticed that several libraries release two packages, one using synchorious IO and … --- ## [Any benefit in using Async when reading a file?](https://discuss.ocaml.org/t/any-benefit-in-using-async-when-reading-a-file/15220)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 1\ **Last updated:** [August 31, 2024, 1:56am UTC](https://discuss.ocaml.org/t/any-benefit-in-using-async-when-reading-a-file/15220 "2024-08-31T01:56:08Z")
Hi. I read a file line by line and do some processing for each line. If I were to use Async to read line by line instead of ordinary reading a file via an Inchannel.input\_line, will there be any difference in performance… --- ## [Async and recursive loop](https://discuss.ocaml.org/t/async-and-recursive-loop/14562)
**Author:** [@kaludis](https://discuss.ocaml.org/u/kaludis)\ **Replies:** 8\ **Last updated:** [May 1, 2024, 6:44pm UTC](https://discuss.ocaml.org/t/async-and-recursive-loop/14562 "2024-05-01T18:44:28Z")
Hello everyone! In the code below I am trying to use async in a recursive loop by creating an async task that should start with a delay of 1 second after the 3rd iteration of the loop. It is obvious that such a solutio… --- ## [Abstracting over monads (Lwt and async and ...)](https://discuss.ocaml.org/t/abstracting-over-monads-lwt-and-async-and/965)
**Author:** [@thomas\_ridge](https://discuss.ocaml.org/u/thomas_ridge)\ **Replies:** 8\ **Last updated:** [October 16, 2017, 6:34pm UTC](https://discuss.ocaml.org/t/abstracting-over-monads-lwt-and-async-and/965 "2017-10-16T18:34:54Z")
Rudi wrote a post which mentioned cohttp and abstracting over Lwt and async monads. http://rgrinberg.com/posts/abandoning-async/ He notes that the standard approach (modules and functors) has some downsides (syntactica… --- ## [Set configuration via command line arguments](https://discuss.ocaml.org/t/set-configuration-via-command-line-arguments/13668)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 1\ **Last updated:** [December 18, 2023, 4:34pm UTC](https://discuss.ocaml.org/t/set-configuration-via-command-line-arguments/13668 "2023-12-18T16:34:02Z")
Hey, I am looking to set some parameters in my program via the command line arguments. I can’t think of a way to do this. I have the following structure of my modules: ModuleA: buffer\_size = 16 depth = 10 ModuleB:… --- ## [Multicore, Async, and Lwt](https://discuss.ocaml.org/t/multicore-async-and-lwt/2687)
**Author:** [@XVilka](https://discuss.ocaml.org/u/XVilka)\ **Replies:** 17\ **Last updated:** [September 15, 2023, 9:08am UTC](https://discuss.ocaml.org/t/multicore-async-and-lwt/2687 "2023-09-15T09:08:50Z")
I am curious, when OCaml multicore is finished and merged mainstream, will programs written with Async and Lwt (or similar) libraries become multithreaded automatically? Will it require major changes in Lwt and Async lib… --- ## [Websocket\_async server, broadcasting messages isn't working as expected](https://discuss.ocaml.org/t/websocket-async-server-broadcasting-messages-isnt-working-as-expected/12630)
**Author:** [@SeedyROM](https://discuss.ocaml.org/u/SeedyROM)\ **Replies:** 2\ **Last updated:** [July 18, 2023, 1:19am UTC](https://discuss.ocaml.org/t/websocket-async-server-broadcasting-messages-isnt-working-as-expected/12630 "2023-07-18T01:19:06Z")
Basically I’m working on a simple websocket server that broadcasts messages to each client listening. I have some code working, I can connect. But something weird happens. When I send the message, the first client gets … --- ## [Async long\_cycles, attribution to code?](https://discuss.ocaml.org/t/async-long-cycles-attribution-to-code/12306)
**Author:** [@Paul\_A\_Steckler](https://discuss.ocaml.org/u/Paul_A_Steckler)\ **Replies:** 1\ **Last updated:** [June 13, 2023, 11:52am UTC](https://discuss.ocaml.org/t/async-long-cycles-attribution-to-code/12306 "2023-06-13T11:52:43Z")
When Async long\_cycles indicates there’s been a long cycle, is there a way to attribute that to a particular piece of code? --- ## [Update on Eio (effects-based direct-style IO for OCaml 5)](https://discuss.ocaml.org/t/update-on-eio-effects-based-direct-style-io-for-ocaml-5/10395)
**Author:** [@talex5](https://discuss.ocaml.org/u/talex5)\ **Replies:** 2\ **Last updated:** [June 5, 2023, 3:49pm UTC](https://discuss.ocaml.org/t/update-on-eio-effects-based-direct-style-io-for-ocaml-5/10395 "2023-06-05T15:49:47Z")
Eio provides an effects-based direct-style IO stack for OCaml 5.0. It aims to be easy to use, secure, well documented, and fast. It consists of a generic cross-platform API, plus optimised backends for different platform… --- ## [Async or Lwt. Multiple source, single reader](https://discuss.ocaml.org/t/async-or-lwt-multiple-source-single-reader/12218)
**Author:** [@vivanov](https://discuss.ocaml.org/u/vivanov)\ **Replies:** 11\ **Last updated:** [May 26, 2023, 6:35pm UTC](https://discuss.ocaml.org/t/async-or-lwt-multiple-source-single-reader/12218 "2023-05-26T18:35:57Z")
Hey, I am trying to figure out how I can use Async or Lwt instead of threads in the scenario with multiple writers and a single reader. Basically, if it were threads I would do the following: open \_and\_connect socket1 … --- ## [Advice for combining multiple monads](https://discuss.ocaml.org/t/advice-for-combining-multiple-monads/10409)
**Author:** [@mooreryan](https://discuss.ocaml.org/u/mooreryan)\ **Replies:** 12\ **Last updated:** [September 5, 2022, 7:43am UTC](https://discuss.ocaml.org/t/advice-for-combining-multiple-monads/10409 "2022-09-05T07:43:27Z")
In a recent project, I was needing to “mix” a couple of different monads: concurrency monad (Async.Deferred), error monad (Core.Or\_error.t), and option monad. I’m using ppx\_let for monadic let bindings, so it isn’t too … --- ## [Working with both Lwt and Async in the same project?](https://discuss.ocaml.org/t/working-with-both-lwt-and-async-in-the-same-project/8423)
**Author:** [@Jon\_Harrop](https://discuss.ocaml.org/u/Jon_Harrop)\ **Replies:** 11\ **Last updated:** [September 21, 2021, 7:24pm UTC](https://discuss.ocaml.org/t/working-with-both-lwt-and-async-in-the-same-project/8423 "2021-09-21T19:24:23Z")
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 lowe… --- ## [Async rpc parallel worker how to report errors](https://discuss.ocaml.org/t/async-rpc-parallel-worker-how-to-report-errors/7433)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 0\ **Last updated:** [March 9, 2021, 8:02pm UTC](https://discuss.ocaml.org/t/async-rpc-parallel-worker-how-to-report-errors/7433 "2021-03-09T20:02:22Z")
I’m currently trying to understand some of the internals of the rpc\_parallel library. The issue I’m having is that a connection to a local worker is dying randomly. I think that that worker may be raising an exception … --- ## [Async.Writer.stderr stuck after process fork](https://discuss.ocaml.org/t/async-writer-stderr-stuck-after-process-fork/7344)
**Author:** [@pmahoney](https://discuss.ocaml.org/u/pmahoney)\ **Replies:** 5\ **Last updated:** [March 5, 2021, 5:31am UTC](https://discuss.ocaml.org/t/async-writer-stderr-stuck-after-process-fork/7344 "2021-03-05T05:31:15Z")
I’m experimenting with async, core, and a pre-forking tcp server. I noticed that Log.Global.info was not logging anything in my child processes, but only if the parent process logged something before forking. I narrowed… --- ## [Lwt alternative to async.pipe](https://discuss.ocaml.org/t/lwt-alternative-to-async-pipe/7265)
**Author:** [@mattpallissard](https://discuss.ocaml.org/u/mattpallissard)\ **Replies:** 3\ **Last updated:** [February 13, 2021, 1:53am UTC](https://discuss.ocaml.org/t/lwt-alternative-to-async-pipe/7265 "2021-02-13T01:53:12Z")
Hey all, I’m new to the ocaml ecosystem and I’m trying to get my bearings on libraries and conventions around common operations. I have some code that downloads a lot of large files. Currently I’m doing this with Cohtt… --- ## [How can I set the priorities of tasks in async or lwt](https://discuss.ocaml.org/t/how-can-i-set-the-priorities-of-tasks-in-async-or-lwt/7058)
**Author:** [@arbipher](https://discuss.ocaml.org/u/arbipher)\ **Replies:** 12\ **Last updated:** [January 28, 2021, 3:45pm UTC](https://discuss.ocaml.org/t/how-can-i-set-the-priorities-of-tasks-in-async-or-lwt/7058 "2021-01-28T15:45:04Z")
Hi all, I am porting my handwritten coroutine to async or lwt. I read their manuals, RWO chapter and lwt tutorial, but I don’t figure out how to assign a priority of a Deferred.t or Lwt.t so that the scheduler can pick … --- ## [Causes of long futex calls using Async](https://discuss.ocaml.org/t/causes-of-long-futex-calls-using-async/6956)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 4\ **Last updated:** [December 15, 2020, 3:10pm UTC](https://discuss.ocaml.org/t/causes-of-long-futex-calls-using-async/6956 "2020-12-15T15:10:19Z")
I’m trying to debug a performance problem currently. The issue is that I have several nodes talking to each other via Async Rpcs and a single node which acts as a gateway to clients. When the gateway doesn’t communiate … --- ## [Factors affecting async cycle length](https://discuss.ocaml.org/t/factors-affecting-async-cycle-length/6782)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 0\ **Last updated:** [November 16, 2020, 7:38pm UTC](https://discuss.ocaml.org/t/factors-affecting-async-cycle-length/6782 "2020-11-16T19:38:02Z")
I’m trying to improve the behavior of a system while it is under load. The specific issue is that I can’t exert backpressure to the externally facing async rpc handler, so when that is overloaded, the async cycle time in… --- ## [Async\_rpc backpressure](https://discuss.ocaml.org/t/async-rpc-backpressure/6758)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 0\ **Last updated:** [November 13, 2020, 10:01am UTC](https://discuss.ocaml.org/t/async-rpc-backpressure/6758 "2020-11-13T10:01:50Z")
Is it possible to apply tcp backpressure onto a Async\_rpc server? The usage case I’m having is where requests are piling up on a externally facing server, while waiting for a response on the internal server. --- ## [How to prevent incomming async\_rpc's from delaying/starving high priority jobs](https://discuss.ocaml.org/t/how-to-prevent-incomming-async-rpcs-from-delaying-starving-high-priority-jobs/6686)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 16\ **Last updated:** [November 2, 2020, 6:59pm UTC](https://discuss.ocaml.org/t/how-to-prevent-incomming-async-rpcs-from-delaying-starving-high-priority-jobs/6686 "2020-11-02T18:59:01Z")
I’m working on a paxos implementation and am currently using the Async\_rpc library for my communcation layer. The issue I’m having is that when the system is under load, the client requests coming in mean that the data g… --- ## [\[mystery solved\] Compiling with continuations: flambda and performance](https://discuss.ocaml.org/t/mystery-solved-compiling-with-continuations-flambda-and-performance/6621)
**Author:** [@Chet\_Murthy](https://discuss.ocaml.org/u/Chet_Murthy)\ **Replies:** 7\ **Last updated:** [October 16, 2020, 10:22pm UTC](https://discuss.ocaml.org/t/mystery-solved-compiling-with-continuations-flambda-and-performance/6621 "2020-10-16T22:22:02Z")
Aha. Needed a little more care with the placing of abstractions for continuations. Erasing post, b/c now it all works as desired. Restoring the deleted post: I was recently chewing over monadic concurrency, and got … --- ## [Async writer, how do writes and fsync interleve](https://discuss.ocaml.org/t/async-writer-how-do-writes-and-fsync-interleve/6541)
**Author:** [@Cjen1](https://discuss.ocaml.org/u/Cjen1)\ **Replies:** 2\ **Last updated:** [October 4, 2020, 7:11am UTC](https://discuss.ocaml.org/t/async-writer-how-do-writes-and-fsync-interleve/6541 "2020-10-04T07:11:38Z")
Yet another how to async question :slight\_smile: I’m trying to write a relatively low latency write ahead log. I had it running in Lwt but after seeing how high performance the rpc library was I am porting it over to As… --- ## [Migrating an Async project to Lwt, a short primer](https://discuss.ocaml.org/t/migrating-an-async-project-to-lwt-a-short-primer/5908)
**Author:** [@mbacarella](https://discuss.ocaml.org/u/mbacarella)\ **Replies:** 1\ **Last updated:** [June 3, 2020, 6:30pm UTC](https://discuss.ocaml.org/t/migrating-an-async-project-to-lwt-a-short-primer/5908 "2020-06-03T18:30:00Z")
Consider this a post where I think aloud about my experience migrating an Async project to Lwt. I’ve spent about a weekend doing such a thing, and if, in the process of talking about it here I can save a few people an h… --- ## [Can't run example code from the chapter on concurrent programming from RWO](https://discuss.ocaml.org/t/cant-run-example-code-from-the-chapter-on-concurrent-programming-from-rwo/5678)
**Author:** [@ppargc1a](https://discuss.ocaml.org/u/ppargc1a)\ **Replies:** 4\ **Last updated:** [May 1, 2020, 12:23pm UTC](https://discuss.ocaml.org/t/cant-run-example-code-from-the-chapter-on-concurrent-programming-from-rwo/5678 "2020-05-01T12:23:17Z")
I’m reading the chapter on concurrent programming in RWO but I can’t seem to run the example code. I copy pasted it but whenever I try to build with dune build main.exe it always gives this error: Error: Unbound value C… [Next page](https://discuss.ocaml.org/tag/async/29.md?match_all_tags=true&page=1&tags%5B%5D=async)