Etc is not Ractor-safe currently

[eregon]

• See https://bugs.ruby-lang.org/issues/21115
• Fixes Etc is not Ractor-safe but is marked as such #50

I think this makes sense for now to address the segfault.
Of course it can be improved later to use explicit locking.

[nobu]

I think methods from Etc.sysconfdir to Etc.nprocessors are ractor-safe.

[eregon]

I think methods from Etc.sysconfdir to Etc.nprocessors are ractor-safe.

Agreed, so I marked those as Ractor-safe and the rest as Ractor-unsafe, and added tests.

[nobu]

I think these 3 are probably MT-safe, and possibly also pathconf.

[eregon]

Right, I'll add them.
And systmpdir seems fine too, all functions it calls take a buffer (for the path) so should be thread-safe.

I'll add a test calling these functions in parallel to try to ensure they are indeed thread/Ractor-safe.
Feel free to review more functions and mark them as safe later, I would just recommend to add them to test_ractor_parallel to check if they are indeed thread/Ractor-safe.

[eregon]

I think methods from Etc.sysconfdir to Etc.nprocessors are ractor-safe.

Actually sysconfdir doesn't work in a Ractor: https://github.com/ruby/ruby/actions/runs/14069312270/job/39399502142#step:12:941 because it tries to access RbConfig::CONFIG if LOAD_RELATIVE.
So I'll just mark it as Ractor-unsafe then: #54
OTOH I'm happy to see --enable-load-relative is tested in CI.

[eregon]

Unfortunately there are more problems, which might be in Etc functions or Ractor bugs.
The test has been pended in ruby/ruby#12992

I have seen this failure:
https://github.com/ruby/ruby/actions/runs/14094646363/job/39479353266?pr=12984#step:14:814

  TestEtc#test_ractor_parallel [/Users/runner/work/ruby/ruby/src/test/etc/test_etc.rb:178]:
  assert_separately failed with error message
  pid 47346 exit 0
  | [BUG] pthread_mutex_lock: Invalid argument (EINVAL)
  | ruby 3.5.0dev (2025-03-26T22:25:25Z pull/12984/merge 1ea32181b7) +PRISM [arm64-darwin23]
  | 
  | -- Crash Report log information --------------------------------------------
  |    See Crash Report log file in one of the following locations:
  |      * ~/Library/Logs/DiagnosticReports
  |      * /Library/Logs/DiagnosticReports
  |    for more details.
  | Don't forget to include the above Crash Report log file in bug reports.
  | 
  | -- Control frame information -----------------------------------------------
  | 
  | 
  | -- Threading information ---------------------------------------------------
  | Total ractor count: 1
  | Ruby thread count for this ractor: 0
  | 
  | -- C level backtrace information -------------------------------------------
  | [BUG] Segmentation fault at 0xfffffffffffffff8
  | ruby 3.5.0dev (2025-03-26T22:25:25Z pull/12984/merge 1ea32181b7) +PRISM [arm64-darwin23]
  | 
  | -- Crash Report log information --------------------------------------------
  |    See Crash Report log file in one of the following locations:
  |      * ~/Library/Logs/DiagnosticReports
  |      * /Library/Logs/DiagnosticReports
  |    for more details.
  | Don't forget to include the above Crash Report log file in bug reports.
  | 
  | Crashed while printing bug report
  | [IMPORTANT]
  | Don't forget to include the Crash Report log file under
  | DiagnosticReports directory in bug reports.
  |

Mentioned in https://ruby.slack.com/archives/C02A3SL0S/p1743044607025709