Not registered error

[Humam-Alhusaini]

This is the repository. I'm stumped as to why I am getting this error.

thread 'main' panicked at src/lib.rs:23:1:
OCaml closure with name 'print_local_def_id' not registered
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Fatal error: no domain lock held
Aborted (core dumped)

My first thought was to check if .exe.o was missing, but that was not the case. I also made sure to check if the Callback.register name is correct, which it is.

The code is really short, about 200 lines, so I'm wondering if you can see any obvious errors? It was working fine in the first commit, but that isn't that much different from the current one.

Thanks

[tizoc]

@Tralalero-Tralalal hmmm I need to investigate it more deeply, something fishy is going on. Sorry, I am making lots of API and internal changes, it is not very well tested yet.

In the meantime you can try the approach used in the tests:

fn ensure_ocaml_runtime_initialized() {
    use ocaml_interop::OCamlRuntimeStartupGuard;

    static INIT: std::sync::Once = std::sync::Once::new();
    static mut OCAML_RUNTIME: Option<OCamlRuntimeStartupGuard> = None;

    INIT.call_once(|| {
        let guard = OCamlRuntime::init().expect("Failed to initialize OCaml runtime");
        unsafe {
            OCAML_RUNTIME = Some(guard);
        }
    });
}


pub fn entry_point(id: LocalDefId) {
    ensure_ocaml_runtime_initialized();
    OCamlRuntime::with_domain_lock(|cr: &mut OCamlRuntime| {
        something(cr, id); // now safe
    });
}

[Humam-Alhusaini]

@tizoc Using that gave me a different error

thread 'main' panicked at src/lib.rs:23:1:
OCaml closure with name 'print_local_def_id' not registered
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[tizoc]

@Tralalero-Tralalal how should I run it, just cargo run ?

I am using this diff:

diff --git a/ocaml/callable.ml b/ocaml/callable.ml
index 59dd8ab..f30c22e 100644
--- a/ocaml/callable.ml
+++ b/ocaml/callable.ml
@@ -7,7 +7,9 @@ type localDefId = {
 }

 let print_local_def_id (id: localDefId ) =
-  print_int id.local_def_index.private_use_as_methods_instead
+  print_int id.local_def_index.private_use_as_methods_instead;
+  print_newline ();
+  flush stdout

 let () =
   print_endline "Registering print_local_def_id...";
diff --git a/src/lib.rs b/src/lib.rs
index 995dab2..a309503 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28,9 +28,24 @@ fn something(cr: &mut OCamlRuntime, record: LocalDefId) {
     let ocaml_variant = record.to_boxroot(cr);
     let _result = print_local_def_id(cr, &ocaml_variant);
 }
+
+fn ensure_ocaml_runtime_initialized() {
+    use ocaml_interop::OCamlRuntimeStartupGuard;
+
+    static INIT: std::sync::Once = std::sync::Once::new();
+    static mut OCAML_RUNTIME: Option<OCamlRuntimeStartupGuard> = None;
+
+    INIT.call_once(|| {
+        let guard = OCamlRuntime::init().expect("Failed to initialize OCaml runtime");
+        unsafe {
+            OCAML_RUNTIME = Some(guard);
+        }
+    });
+}
+
 pub fn entry_point(id: LocalDefId) {
-    let _guard = OCamlRuntime::init().unwrap();
+    ensure_ocaml_runtime_initialized();
     OCamlRuntime::with_domain_lock(|cr| {
         something(cr, id); // now safe
     });

and from cargo run I get:

    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
     Running `target/debug/rust-caller`
Registering print_local_def_id...
3

[tizoc]

@Tralalero-Tralalal just in case, delete _build and target and try again, there could be old leftover OCaml object files with an older version that didn't register the function.

[Humam-Alhusaini]

@tizoc
Deleting the target and _build folders worked! This gave me something like this

Registering print_local_def_id...
3
Fatal error: no domain lock held
Aborted (core dumped)

However, adding your diff fixed the fatal error.

[tizoc]

Great, I will let you know once I have fixed the issue, because there is without doubt a bug there. Also the Rust->OCaml build setup is a bit messy right now, I am working on new docs and trying to improve that.

[tizoc]

@Tralalero-Tralalal just published v0.11.2. It should fix the Fatal error: no domain lock held issue.

The cause was that I forgot to re-acquire the runtime lock when the runtime startup guard is locked, which caused the shutdown call to fail with that error.

[Humam-Alhusaini]

@tizoc Thanks.

If I wanted to contribute, where would I start

[tizoc]

@Tralalero-Tralalal ideally anything you find that you need and is missing. Reporting any issues you find too (I am making some big changes to this crate after now having worked on it for a long while, and I am probably breaking a few things in the process).

The main aspect I am trying to solve right now is the new documentation (see #65), and part of that involves figuring out how to simplify and streamline the building of Rust programs that call OCaml code.

Then I would like to come up with a solution to what in my experience is the biggest pitfall of using ocaml-interop to write FFI code: it is easy to have the function signatures (and complex type declarations) not match between OCaml and Rust, and the result is most of the time a segfault at runtime in the best case, and corrupted data in the worst case.

There is https://github.com/o1-labs/ocaml-gen for ocaml-rs, and a simpler solution (but for a smaller scope) that ocaml-rs itself provides: annotating exported functions with sig declarations.

Btw note that on the main branch ocaml_export! has been removed and replaced with a more featureful proc macro (#64), but it has not been tested a lot yet.