Thread-level events explode due to empty stack #3835
Description
Environment
I believe this affects all JRuby 9k versions that support Thread begin/end trace events (probably all released versions) up through 9.1).
Expected Behavior
MRI in 2.1 or 2.2 added the ability to trace the begin and end of thread life via both set_trace_func and the TracePoint API.
Actual Behavior
On JRuby, the thread begin/end events currently error out, because at least in the case of set_trace_func it is not possible to acquire a thread for the necessary binding:
[--dev] ~/projects/jruby $ jruby --debug -e "set_trace_func(proc {|*a| p a}); Thread.new { return }"
["c-call", "-e", 1, :new, #<Binding:0x8e24743>, #<Class:Thread>]
["c-call", "-e", 1, :initialize, #<Binding:0x23fe1d71>, Thread]
["c-return", "-e", 1, :initialize, #<Binding:0x1d371b2d>, Thread]
["c-return", "-e", 1, :new, #<Binding:0x13eb8acf>, #<Class:Thread>]
Exception in thread "Ruby-0-Thread-1: -e:1" java.lang.ArrayIndexOutOfBoundsException: -1
at org.jruby.runtime.ThreadContext.getCurrentFrame(ThreadContext.java:465)
at org.jruby.runtime.ThreadContext.currentBinding(ThreadContext.java:984)
at org.jruby.Ruby$CallTraceFuncHook.eventHandler(Ruby.java:3133)
at org.jruby.runtime.EventHook.event(EventHook.java:30)
at org.jruby.Ruby.callEventHooks(Ruby.java:3214)
at org.jruby.runtime.ThreadContext.trace(ThreadContext.java:641)
at org.jruby.runtime.ThreadContext.trace(ThreadContext.java:637)
at org.jruby.internal.runtime.RubyRunnable.run(RubyRunnable.java:98)
at java.lang.Thread.run(Thread.java:745)
This affects set_trace_func for sure, since it always tries to acquire a binding. It may not affect TracePoint.
This is a regression because 1.7 did not have these top-level thread events, and on 9k they prevent even simple set_trace_func from working properly.