fix(rpc): remove threads

replace them with evented io based on Unix.select

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: 2d55627f-c73c-41a0-8e41-e57482f0edbe -->

CHANGES.md

@@ -29,6 +29,9 @@ Unreleased
 - Revert #7415 and #7450 (Resolve `ppx_runtime_libraries` in the target context when
   cross compiling) (#7887, fixes #7875, @emillon)
 
+- Fix RPC buffer corruption issues due to multi threading. This issue was only
+  reproducible with large RPC payloads (#7418)
+
 3.8.0 (2023-05-23)
 ------------------
 

boot/libs.ml

@@ -33,6 +33,7 @@ let local_libraries =
   ; ("otherlibs/dune-private-libs/section", Some "Dune_section", false, None)
   ; ("src/dune_lang", Some "Dune_lang", false, None)
   ; ("vendor/opam-file-format", None, false, None)
+  ; ("src/dune_async_io", Some "Dune_async_io", false, None)
   ; ("src/fiber_util", Some "Fiber_util", false, None)
   ; ("src/dune_cache_storage", Some "Dune_cache_storage", false, None)
   ; ("src/dune_cache", Some "Dune_cache", false, None)