-
this is happening and is legal: then I need to completely rethink my
understanding of data structure consistency in NodeJS.
…
-
it’s not actually happening and the call stack is a lie: but then I need
some other explanation for the data structure inconsistency that my
assertions are observing.
It’s a little bit of #1 and #3.
Your basic understanding of how asynchronous concurrency works in Node is
sound, but there’s one piece you seem to be missing: when you call an
asynchronous function (like request()) and pass it a callback, that
callback is going to be called on the other side of some kind of
asynchronous I/O operation (in request’s case, most likely reading the
response stream after making an external HTTP request). At some point, a
callback function (in this case, probably created by request) got handed
off to a lower-level operation (perhaps within fibers) that handed it over
to MakeCallback on the C++ side of node, which interfaces to the JS side
via _tickCallback when the runtime indicates that there are data available
to be read back from libuv.
My guess is that something about how node-fibers handles suspension and
resumption of its continuations / coroutines is interacting with the V8
stack in a funky way, but that the code is basically executing as expected.
I don’t use fibers, and maybe one of the people here who does can pitch in
here, but I think that’s not a deal breaker here – the only real
peculiarity they cause here is that because of how they staple call stacks
together, you’re seeing a stack trace that bridges an async call boundary.
Does that make sense?
F
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