src: simplify native_immediate_callbacks

[joyeecheung]

• Use std::list instead of std::vector because we do not need
  random access.
• Use list.erase instead of moving elements then resizing to
  remove the first n elements in the list for simplicity and
  avoiding reallocation.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

[joyeecheung]

CI: https://ci.nodejs.org/job/node-test-pull-request/13667/

[addaleax]

Did you benchmark this? Using a std::list is usually slower and almost always has more memory overhead than std::vector if the elements are small… I did consider using a std::list for this, but chose not to because of that.

[joyeecheung]

@addaleax I didn't. Should I use the HTTP2 benchmark (looks like that's where the native immediates are extensively used) or create an addon benchmark like bencharmk/misc/function_call?

[addaleax]

Hm … an addon benchmark sounds like a lot of work for something like this, but I’m not sure that any particular subsystem uses this enough to reflect significant changes.

(which might also mean that it probably doesn’t quite matter that much anyway… 😄 )

[joyeecheung]

Started a HTTP2 benchmark: https://ci.nodejs.org/job/benchmark-node-micro-benchmarks/140

[addaleax]

@joyeecheung It seems hard to write an addon benchmark, because getting addon and core ABI align is tricky due to all the flags we have, and because this patch itself switches the ABI… here’s what I’ve come up with by #defineing the right flags manually: https://gist.github.com/addaleax/95df2705479cf7c7cc2f3714ee4b36f9

I’m getting about 44 Mops/sec with the current implementation, and about 19.5 Mops/sec with this PR.

I’d leave it to you to make the call to say whether this is worth it, given that it doesn’t seem to affect the actual application code all that much.

But generally, if you have ideas for how to actually get that benchmark (or one like it) into core, that would be cool. 😄

[joyeecheung]

@addaleax I'll close because I don't think it's worth the cost, thanks for writing up the benchmark!

I've attempted to run node-gyp from within the benchmark script before but failed to make it play with child_process (refs: #16934 ), probably can figure it out sometime later