[ruby-core:28712] When a trace hook raises an exception, should it terminate the program?

In Ruby 1.8 and the Ruby 1.9 trunk when running a trace hook that raises an
exception not caught by the hook, the program terminates -- whether or not
there is a rescue further up the call stack, i.e. in the non-hook body.

Ruby 1.9 also gives a stack trace, while Ruby 1.8 doesn't.

How do JRuby, IronRuby and Rubinius and other Rubies handle this? And what
do the specifications say?

If it is the case that raising an exception in a trace hook unconditionally
terminates the hooked program, programmers that want to write a trace hook
that plays nice with programs it hooks against should wrap the hook in a
begin/rescue block. Or make sure your code never raises an uncaught
exception.

Here is some test code followed by output:

s = Proc.new {  # line 1
  |event, file, lineno, mid, binding, klass|  # line 2
  puts "#{event} #{mid} :#{lineno}"   # line 3
  raise RuntimeError   # line 4
}   # line 5
begin   # line 6
  set_trace_func(s)   # line 7
  puts "after trace func"  # line 8
rescue   # line 9
  puts "Rescued"  # line 10
end   # line 11


For Ruby 1.8.7 2009-07-12 patchlevel 174:

$ /usr/bin/ruby trace-bug.rb
line  trace-bug.rb:8
line  trace-bug.rb:10
c-call backtrace trace-bug.rb:10
c-call write trace-bug.rb:10

For Ruby 1.9 trunk (Rev 26961):

$ ./ruby trace-bug.rb
c-return set_trace_func trace-bug.rb:7
c-call === trace-bug.rb:10
trace-bug.rb:4:in `block in <main>': RuntimeError (RuntimeError)
    from trace-bug.rb:10:in `rescue in <main>'
    from trace-bug.rb:6:in `<main>'

By the way, also note that Ruby 1.9 includes as a trace event the C return
from set_trace_func. I find this not quite right. In a patch to an
experimental Ruby to add better debugging support, this event is removed.

I'll open a ticket in Redmine if it is decided this is something worth
reporting.

Thanks.