Ruby 3.2.0 gauge error for the RubyVM.stat API changes

[intrip]

Current behavior

The gem started logging the following error in our app after we upgraded to Ruby 3.2.0:

E, [2023-01-11T09:02:59.815928 #1] ERROR -- ddtrace: [ddtrace] (/usr/local/bundle/ruby/3.2.0/gems/ddtrace-1.5.0/lib/datadog/core/metrics/client.rb:137:in `rescue in gauge') Failed to send gauge stat. Cause: ArgumentError ArgumentError Source: /usr/local/bundle/ruby/3.2.0/gems/ddtrace-1.5.0/lib/datadog/core/metrics/client.rb:133:in `gauge'

Expected behaviour

The error shouldn't occur.

Steps to reproduce

Use any version of the ddtrace library (even the latest) on Ruby 3.2.0. When a metric flush occurs the above error is logged.

How does ddtrace help you?

The library should handle correctly the new Ruby 3.2.0 RubyVM.stat changes and rely on the new key :constant_cache_invalidations instead of :global_constant_state for Ruby >= 3.2.0. It might also gauge the newly added key :constant_cache_misses when available.

See ruby/ruby#5433, https://github.com/DataDog/dd-trace-rb/blob/v1.5.0/lib/datadog/core/environment/vm_cache.rb#L23-L25, newrelic/newrelic-ruby-agent#1436

Environment

• ddtrace version: I've tested with 1.5.0 and 1.8.0 but looks like all the versions are affected
• Configuration block (Datadog.configure ...):
• Ruby version: 3.2.0
• Operating system: Ubuntu Focal
• Relevant library versions:

[marcotc]

Thank you, @intrip.

We are still trying to get our CI to pass in Ruby 3.2: #2497

This issue is covered by tests and I noticed it indeed fails in 3.2.

We'll address this issue when #2497 is merged.

[intrip]

Thank you @marcotc! Sorry I haven't noticed that 3.2 is not supported yet 😅.

Right now I've come up with this monkey patch to workaround it:

Datadog::Core::Environment::VMCache.class_eval do
  module_function
  # Ruby >= 3.2 uses :constant_cache_invalidations instead of :global_constant_state
  # This is a temporary workaround, the correct solution is to report both :constant_cache_invalidations and :constant_cache_misses in DD
  # See https://github.com/ruby/ruby/pull/5433,
  #     https://github.com/DataDog/dd-trace-rb/blob/v1.5.0/lib/datadog/core/environment/vm_cache.rb#L23-L25
  def global_constant_state
    RubyVM.stat[:constant_cache_invalidations]
  end
end

Unfortunately, I've already shipped a Ruby 3.2 upgrade in one of our apps (with this patch). I haven't noticed any other major breakage so far but I'm afraid there are some subtle unnoticed errors, so right now I'm afraid to push forward a Ruby 3.2 upgrade on our main app, which has a lot of traffic.

Do you have any ETA of when the Ruby 3.2 support will be available?

[sohilsathe]

+1

thank you for the support!

[unicornzero]

@intrip Thank you for posting such a comprehensive issue report along with a temporary patch and linked references! This was a huge help to me today. Thank you!

[ivoanjo]

Thanks @intrip for the workaround and everyone for the patience. We're working on a fix for this and expect it to be included on the next dd-trace-rb release.

[unicornzero]

@ivoanjo thank you so much for tackling this issue this week! And thank you for the updates. I want to set a reminder to check for an update so I can remove my patch in my code. What's your best guess as to a possible timeline for the 1.10 release?

[ivoanjo]

We aim to get a new release out every 4-8 weeks, which would put 1.10 towards the end of February/sometime in March.

But, do let us know If this (or any other) issue is blocking or being really annoying for you, that helps us prioritize an earlier release.