This removes the `process._needImmediateCallback` property
and its semantics of having a 1/0 switch that tells C++ whether
immediates are currently scheduled.
Instead, a counter keeping track of all immediates is created,
that can be increased on `setImmediate()` or decreased when an
immediate is run or cleared.
This is faster, because rather than reading/writing a C++ getter,
this operation can be performed as a direct memory read/write via
a typed array. The only C++ call that is left to make is
activating the native handles upon creation of the first
`Immediate` after the queue is empty.
One other (good!) side-effect is that `immediate._destroyed` now
reliably tells whether an `immediate` is still scheduled to run or not.
Also, as a nice extra, this should make it easier to implement
an internal variant of `setImmediate` for C++ that piggybacks
off the same mechanism, which should be useful at least for
async hooks and HTTP/2.
Benchmark results:
$ ./node benchmark/compare.js --new ./node --old ./node-master-1b093cb93df0 --runs 10 --filter immediate timers | Rscript benchmark/compare.R
[00:08:53|% 100| 4/4 files | 20/20 runs | 1/1 configs]: Done
improvement confidence p.value
timers/immediate.js type="breadth" thousands=2000 25.61 % ** 1.432301e-03
timers/immediate.js type="breadth1" thousands=2000 7.66 % 1.320233e-01
timers/immediate.js type="breadth4" thousands=2000 4.61 % 5.669053e-01
timers/immediate.js type="clear" thousands=2000 311.40 % *** 3.896291e-07
timers/immediate.js type="depth" thousands=2000 17.54 % ** 9.755389e-03
timers/immediate.js type="depth1" thousands=2000 17.09 % *** 7.176229e-04
timers/set-immediate-breadth-args.js millions=5 10.63 % * 4.250034e-02
timers/set-immediate-breadth.js millions=10 20.62 % *** 9.150439e-07
timers/set-immediate-depth-args.js millions=10 17.97 % *** 6.819135e-10
PR-URL: https://github.com/nodejs/node/pull/17064
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Anna Henningsen
ae558af7bc