Bug #20059: TracePoint#enable can be called multiple times, increasing the number of invokations

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

[zverok (Victor Shepelev)]

I just stumbled upon this accidentally (created a tracepoint with TracePoint.trace, and then enabled it).

My initial example

trace = TracePoint.trace(:raise) do |tp|
  puts "Exception raised: #{tp.raised_exception.inspect} at #{tp.path}:#{tp.lineno}"
end
trace.enable # shouldn't do this, it was already enabled!
raise "foo"

This prints

Exception raised: #<RuntimeError: foo> at test.rb:5
Exception raised: #<RuntimeError: foo> at test.rb:5

Twice.
If I'll remove the "unnecessary" trace.enable, it prints it once.

So the theory is "multiple enables = multiple invokations of a tracepoint"...

trace = TracePoint.trace(:raise) do |tp|
  puts "Exception raised: #{tp.raised_exception.inspect} at #{tp.path}:#{tp.lineno}"
end
5.times { trace.enable }
raise "foo"

...and indeed, this code prints the "Exception raised:" message 6 times.

I don't see anything about this behavior in the method's docs or class docs, and can't think of a plausible explanation. But it was this way since Ruby 2.0, and either it should be this way, or it bothers nobody :)

I wonder:

• is there a reasonable explanation for this?
• if so, shouldn't it be documented somewhere?..

Or is it some part of a pattern of how the TracePoint works that I am missing here?..

[tenderlovemaking (Aaron Patterson)]

IIRC the tracepoints are just added to a linked list. There's probably no validation as to whether or not that tracepoint has already been added to the linked list (and we just need to do that book keeping)

[kyanagi (Kouhei Yanagita)]

Is this issue the same as #19114?
I have created a pull request for the fix at https://github.com/ruby/ruby/pull/8993.
Does this resolve the problem?

[mame (Yusuke Endoh)]

• Status changed from Open to Closed