[ruby-core:123404] [Ruby Bug#19461] Time.local performance tanks in forked process (on macOS only?)

6 Oct 2025

      Issue #19461 has been updated by ioquatix (Samuel Williams).

Just for reference, on the lastest macOS, the issue still appears:

```
% clang localtime_test.c 
% ./a.out 
Measuring localtime
In parent
  monotonic = 0.002930000
  cputime = 0.002454000
In child
  monotonic = 0.553250000
  cputime = 0.552287000
```

So this is still an issue, in practice.

----------------------------------------
Bug #19461: Time.local performance tanks in forked process (on macOS only?)
https://bugs.ruby-lang.org/issues/19461#change-114772

* 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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