wasm2c: Are module instances truly thread-safe? about wabt

[keithw]

Awesome. In other words, if I encounter any state and data race-related issues with this type of usage, I can assume it's a bug?

Yeah, definitely please let us know.

[jonathanmarvens]

Upon further investigation, the commentary on #2189 and #2332 seem to imply that the module instances are thread-safe, but the semantics aren’t clear.

To be clear, my current understanding is that the runtime is explicitly thread-safe (if each thread is properly initialized via wasm_rt_init_thread()), but individual module instances might be operating in undefined behavior territory when called into from multiple threads.

[keithw]

Normally when we say code is "thread-safe," we're talking about different threads executing code in parallel. Happy to go down that road, but that doesn't seem to be what you're asking about here. If I understand the question, you're just saying, is it okay if a module is instantiated by thread A, and then (after that has provably completed) thread B calls an exported function from that module instance, and then (after that has provably completed) thread C calls an exported function from the same module instance?

Certainly our intention is that this is an easy case and there's no problem. There's no long-lived association between any per-thread state and any particular module instance.

[jonathanmarvens]

If I understand the question, you're just saying, is it okay if a module is instantiated by thread A, and then (after that has provably completed) thread B calls an exported function from that module instance, and then (after that has provably completed) thread C calls an exported function from the same module instance?

Yes, this is exactly what I'm trying to understand. My apologies if I wasn't clear enough.

Certainly our intention is that this is an easy case and there's no problem. There's no long-lived association between any per-thread state and any particular module instance.

Awesome. In other words, if I encounter any state and data race-related issues with this type of usage, I can assume it's a bug?

[jonathanmarvens]

Yeah, definitely please let us know.

Will do. Thank you!

(I'll close this issue now, since I got my answer.)