[ruby-core:123061] [Ruby Bug#19461] Time.local performance tanks in forked process (on macOS only?)

Issue #19461 has been updated by catlee (Chris AtLee).


I ran into this myself, and implemented a workaround here:
https://github.com/ruby/ruby/pull/13968

The idea is to cache our offset from GMT, and then use that in subsequent localtime calculations.
The cache is valid for every second within the same GMT minute.

----------------------------------------
Bug #19461: Time.local performance tanks in forked process (on macOS only?)
https://bugs.ruby-lang.org/issues/19461#change-114379

* Author: ioquatix (Samuel Williams)
* Status: Closed
* 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)
clipboard-202302251716-rh6ma.png (234 KB)


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