Environment Information
$ mise x ruby@jruby -- ruby -v
jruby 10.1.0.0 (4.0.0) 2026-04-20 32f988b78c OpenJDK 64-Bit Server VM 26.0.2+10-55 on 26.0.2+10-55 +indy +jit [arm64-darwin]
$ uname -a
Darwin Konstantins-MBP.localdomain 25.5.0 Darwin Kernel Version 25.5.0: Tue Jun 9 22:28:34 PDT 2026; root:xnu-12377.121.10~1/RELEASE_ARM64_T6041 arm64
No other dependencies are needed to run into this issue.
I found this by tracing which thread a fiber scheduler fiber belongs to.
Expected Behavior
Should trace fiber_switch events (introduced in Ruby 2.3.0)
triggered = false
TracePoint.trace(:fiber_switch) do |tp|
triggered = true
end
Fiber.new { p triggered }.resumeShould print true
Actual Behavior
Raises an exception:
ArgumentError: unknown event: fiber_switch
initialize at org/jruby/ext/tracepoint/TracePoint.java:65
new at org/jruby/RubyClass.java:1058
trace at org/jruby/ext/tracepoint/TracePoint.java:282
<main> at play/trace.rb:3
Environment Information
No other dependencies are needed to run into this issue.
I found this by tracing which thread a fiber scheduler fiber belongs to.
Expected Behavior
Should trace
fiber_switchevents (introduced in Ruby 2.3.0)Should print
trueActual Behavior
Raises an exception: