Multithreading on the single JSRuntime with different JSContext?

[laishere]

I have a use case to run tasks on multiple contexts in parallel.
Currently, I do it with multiple single-context runtime instances.
I am thinking about doing some improvements by reusing the same JSRuntime for different contexts.

The question is: does it support executing js_call in parallel on a single JSRuntime with different JSContext?
Looking at the code, I do see there are many modification statements to the JSRuntime without any locking mechanisms. I didn't check it very carefully if they will be called during the actual execution of js_call.

And one more question is: how much is the overhead difference between single-context runtime vs multi-context runtime per context?

[bnoordhuis]

does it support executing js_call in parallel on a single JSRuntime with different JSContext?

No.

how much is the overhead difference between single-context runtime vs multi-context runtime per context?

You mean how much overhead JSRuntime adds? Not much, but that's arguably the wrong question to ask because multiple JSContexts aren't supported as a memory-saving feature but to make it possible for embedders to implement Realms.

Browser example: main page vs. iframes; different execution contexts but they're accessible to each other.