Bug #8886: TracePoint API inconsistence when raise used

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: 2.1.0
• ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [i686-linux]
• Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN

[deivid (David Rodríguez)]

=begin
When raise command is used, the TracePoint API triggers the following events in the following order

1. RUBY_EVENT_C_CALL to the `raise` method
2. RUBY_EVENT_RAISE
3. RUBY_EVENT_C_RETURN

But what ruby actually does is

1. Push frame into the stack when calling the `raise` c method.
2. Pop frame from the stack
3. And after popping the frame, raise the exception.

As you can see, 2 and 3 are reversed and this messes up byebug and (I guess) other users of the API.

To illustrate I use a similar program as I used in (invalid) #8538

tp = TracePoint.trace do |tp|
  warn "%-8s %-11p" % [tp.event, tp.method_id]
end
raise "bang"

Actual output

c_return :trace     
line     nil        
c_call   :raise     
c_call   :new       
c_call   :initialize
c_return :initialize
c_return :new       
c_call   :backtrace 
c_return :backtrace 
raise    nil        
c_return :raise     
test_bug.rb:4:in `<main>': bang (RuntimeError)

Expected output

c_return :trace     
line     nil        
c_call   :raise     
c_call   :new       
c_call   :initialize
c_return :initialize
c_return :new
c_return :raise     
c_call   :backtrace 
c_return :backtrace 
raise    nil        
test_bug.rb:4:in `<main>': bang (RuntimeError)

I've made a patch that solves the issue and, as a result, the problems byebug is having. Please review and excuse me if I'm not being able to properly explain myself.

Thanks a lot!
=end

[deivid (David Rodríguez)]

Ping. Could @ko1 (Koichi Sasada) or someone review this and (hopefully) merge it? I've been using it for the last week without any issues.

Thanks!

[drbrain (Eric Hodel)]

• Status changed from Open to Assigned

[ko1 (Koichi Sasada)]

• Category set to core
• Target version set to 2.1.0

[ko1 (Koichi Sasada)]

deivid (David Rodríguez) wrote:

Expected output

c_return :trace     
line     nil        
c_call   :raise     
c_call   :new       
c_call   :initialize
c_return :initialize
c_return :new
c_return :raise     
c_call   :backtrace 
c_return :backtrace 
raise    nil        
test_bug.rb:4:in `<main>': bang (RuntimeError)

Could you tell me why it is expected?

:raise event occures in raise method. So the current behavior works for me.

[deivid (David Rodríguez)]

• File raise_exception_inside_raise_method.patch raise_exception_inside_raise_method.patch added

I don't think ruby works like that right now. If :raise event occurs inside raise method, then when I print the backtrace of an exception, I should get the raise method as the first frame, just like when I do Thread.current.backtrace_locations I get backtrace_locations as the first frame.

In my first patch I tried to adapt TracePoint API's behaviour to ruby's behaviour, but I agree that ":raise event occures in raise method" behaviour makes more sense.

So I attach another patch to fix that.

Thanks @ko1 (Koichi Sasada)!

[deivid (David Rodríguez)]

So, any opinions on this @ko1 (Koichi Sasada)?

I'm handling this edge case in byebug manually so it's not a big deal but it'd be nice to get this fixed in ruby, either adapting the TracePoint API to ruby's behavior or changing how ruby behaves.

Thanks.

[ko1 (Koichi Sasada)]

Sorry for long absence.

Your patch makes sense for me.
I'll apply it.

Thank you very much.

[ko1 (Koichi Sasada)]

• Status changed from Assigned to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r44133.
David, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• eval.c (rb_raise_jump): pop frame after setup exception.
  Patches by deivid (David Rodriguez). [Bug #8886]
• test/minitest/test_minitest_unit.rb: catch up this change.
• test/ruby/test_backtrace.rb: ditto.
• test/ruby/test_settracefunc.rb: ditto.

[ko1 (Koichi Sasada)]

• Status changed from Closed to Open
• Assignee changed from ko1 (Koichi Sasada) to matz (Yukihiro Matsumoto)
• Priority changed from Normal to 5

I committed it and rubyspec found an issue of incompatibility.

raise
#=>
ruby 2.1.0dev (2013-12-11 trunk 44136) [i386-mswin32_110]
t.rb:2:in raise': unhandled exception from t.rb:2:in '

ruby 2.0.0p317 (2013-09-15 revision 42947) [i386-mswin32_110]
t.rb:2:in `': unhandled exception

On backtrace, `raise' frame is available. I'm not sure it is acceptable or not.

One minor advantage of output `raise' frame on backtrace is, we can understand this error is occurred by raise method.

[ko1 (Koichi Sasada)]

A bit strange for the following case?

---

raise("should not reach here")
#=>
ruby 2.1.0dev (2013-12-11 trunk 44136) [i386-mswin32_110]
t.rb:1:in raise': should not reach here (RuntimeError) from t.rb:1:in '

#=>
ruby 2.0.0p317 (2013-09-15 revision 42947) [i386-mswin32_110]
t.rb:1:in `': should not reach here (RuntimeError)

[ko1 (Koichi Sasada)]

I asked Matz and he said "I prefer to remove `raise' line in backtrace".
So I will revert r44133 and introduce the first patch.

[deivid (David Rodríguez)]

It doesn't make a lot of difference to me, so if this is actually spec, I agree with keeping the current behaviour and just adapting the TracePoint API.

Thanks a lot Koichi! :)

[ko1 (Koichi Sasada)]

• Status changed from Open to Closed

This issue was solved with changeset r44139.
David, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

• eval.c (rb_raise_jump): call c_return hook immediately after
  popping `raise' frame.
  Patches by deivid (David Rodriguez). [Bug #8886]
• test/ruby/test_settracefunc.rb: catch up this fix.

[ko1 (Koichi Sasada)]

deivid (David Rodríguez) wrote:

It doesn't make a lot of difference to me, so if this is actually spec, I agree with keeping the current behaviour and just adapting the TracePoint API.

r44139 makes it consistent with your patch. Thanks!

[deivid (David Rodríguez)]

Great, thanks a lot!!