[ruby-core:112571] [Ruby master Bug#19461] Time.local performance tanks in forked process (on macOS only?)

Issue #19461 has been updated by nobu (Nobuyoshi Nakada).

File localtime_test.c added

Rewritten.

```
$ clang localtime_test.c && ./a.out
Measuring in parent
  localtime_r = 0.002384000
  localtime   = 0.001939000
Measuring in child
  localtime_r = 0.576143000
  localtime   = 0.591077000
```

----------------------------------------
Bug #19461: Time.local performance tanks in forked process (on macOS only?)
https://bugs.ruby-lang.org/issues/19461#change-102020

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
The following program demonstrates a performance regression in forked child processes when invoking `Time.local`:

```ruby
require 'benchmark'
require 'time'

def sir_local_alot
  result = Benchmark.measure do
    10_000.times do
      tm = ::Time.local(2023)
    end
  end
  $stderr.puts result
end

sir_local_alot

pid = fork do
  sir_local_alot
end

Process.wait(pid)
```

On Linux the performance is similar, but on macOS, the performance is over 100x worse on my M1 laptop.


---Files--------------------------------
localtime_test.c (1.28 KB)
localtime_test.c (1.21 KB)


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