bug: Cannot use allo-isolate in two libraries with static linking because of symbol name duplication

[fzyzcjy]

When a user is using two packages having allo-isolate, and doing static linking, the symbol store_dart_post_cobject is used in two Rust crates, and thus it seems that the linker will throw away one symbol completely. Then, when calling store_dart_post_cobject, only one of the two Rust crates will actually store that pointer. The other crate will never store it, and thus allo-isolate cannot work at all.

/cc @AlexV525

[shekohex]

How is it possible to have two allo-isolate in a single binary? It should only be one! Unless we have two different versions and cargo decided to link both? Which in this case is bad! I would recommend dedup Cargo.lock and find out which crate that uses the older version of allo-isolate and update it, should be only one if they both have same version.

[fzyzcjy]

How is it possible to have two allo-isolate in a single binary?

• The app uses Dart lib A and lib B
• lib A uses a rust crate C. Thus crate C (and its dependency allo-isolate) are compiled into library_c.a and statically links to the final app
• lib B similarly use crate D, and library_d.a

In this case we have trouble...

That said, Flutter's official template provide dynamic linking now (IIRC years ago it was static linking), so may not be a problem, unless users choose to do static linking.

[shekohex]

That said, Flutter's official template provide dynamic linking now (IIRC years ago it was static linking), so may not be a problem, unless users choose to do static linking.

iOS is always static linked, no?

But I hear you, I'm open to other ideas to set up the bridge through FFI, maybe each library author would choose their own exposed function? Through a macro, for example?

Like the following:

// in allo-isolate code lib.rs
#[macro_export]
macro_rules! mk_store_dart_post_cobject {
	($name:ident) => {
		#[no_mangle]
		pub unsafe extern "C" fn $name(ptr: ::allo_isolate::ffi::DartPostCObjectFnType) {
			::allo_isolate::POST_COBJECT.store(Some($ptr), Ordering::Relaxed);
		}
	},
}

// in my-awesome-crate lib.rs
allo_isolate::mk_store_dart_post_cobject!(my_awesome_crate_store_dart_post_cobject);

This way, we will not have a duplicated symbols.

[fzyzcjy]

iOS is always static linked, no?

I also did that, but seems no today, which is surprising. -> https://github.com/flutter/flutter/blob/8b6277e63868c2029f1e2327879b7899be44fbe2/packages/flutter_tools/templates/plugin_ffi/lib/projectName.dart.tmpl#L47-L58

Through a macro, for example?

It sounds like an option.
For FRB, a solution is to create a (generated) wrapper function.

Anyway, as mentioned above, this is not a problem for the dynamic linking now.