Async call to node api

[sunoru]

All uv_run calls for the event loop of nodeJS from either idle handles of Julia event loop or scheduled tasks (e.g. by @async) raises RangeError: Maximum call stack size exceeded.

For example,

using NodeCall
import NodeCall: UvRunMode, UV_RUN_NOWAIT

function sometask()
    node"setTimeout(() => console.log('Done'), 2000)"
    loop = node_uvloop()
    @async let ret = 1
        while ret != 0
            sleep(0.5)  # or `yeild()` to make the task not blocking
            ret = @ccall :libjlnode.uv_run(loop::Ptr{Cvoid}, UV_RUN_NOWAIT::UvRunMode)::Cint
        end
    end
end

p = sometask()
wait(p)

throws

undefined:0


RangeError: Maximum call stack size exceeded
Thrown at:

No matter which UvRunMode is used.

[sunoru]

Actually, any async functions that invoke any node-API would throw this. It is because the API must be used in the main thread.

Even showing js values in REPL will throw this error:

julia> using NodeCall
julia> a = node"()=>{}"
┌ Debug: napi_string_expected
└ @ NodeCall ~/pro/julia-packages/NodeCall/src/utils.jl:31
Error showing value of type JsFunction{Nothing}:
ERROR: "Maximum call stack size exceeded"

julia> println(a)
JsFunction{Nothing}: ()=>{}

julia> @async println(a)
┌ Debug: napi_string_expected
└ @ NodeCall ~/pro/julia-packages/NodeCall/src/utils.jl:31
Task (failed) @0x00007fe0ab53fc70
Maximum call stack size exceeded

[sunoru]

Try using N-API's async APIs.

[sunoru]

https://nodejs.org/docs/latest-v14.x/api/n-api.html#n_api_asynchronous_thread_safe_function_calls

We probably have to invoke by napi_threadsafe_function.

Maybe it's not worth supporting @async, since we can always use @node_async to let NodeJS control the event loop.

Perhaps a function can be provided to wrap a Task with an async context?

I'm still not sure how the other napi_ functions should be used in an async environment. Will test later.

[sunoru]

Instead of wrapping Tasks, we can directly modify napi_call to invoke napi_create_threadsafe_function if current_task() != global_task().

See the threading branch and https://github.com/sunoru/jlnode/tree/threading