Modules are sensitive to deadlock

[calebzulawski]

I have a complex example of a function that returns a module, used by another module, results in a deadlock.

uses = { export = [make-module $args] } deadlocks, but

c++:Module :mod = make-module $args
...
uses = { export = [$mod] }

does not deadlock. Alternatively, uses = { export = [std:eval-id <| make-module $args] } also avoids the deadlock.

Interestingly, adjusting the scopes of variables within make-module can induce the deadlock even with these changes, which makes me think the problem is in the hypothetical make-module (which I have not been able to make a minimal reproduction for).

[afranchuk]

Yeah, this is almost certainly a deadlock in identity calculation. The calculation needs to be improved such that if a value's identity is being computed and it needs to compute its own identity as part of that, it'll just return 0 or some other fixed value. That's why it is caused by your make-module implementation, and why std:eval-id or evaluating the module earlier avoids the problem. Usually the only way to create recursive values (which could cause self-dependency in identities) is with load, since std:recurse automatically handles this.