From: "mame (Yusuke Endoh)" <noreply@...>
Date: 2021-08-20T04:14:33+00:00
Subject: [ruby-core:105020] [Ruby master Feature#16889] TracePoint.enable { ... } also activates the TracePoint for other threads, even outside the block

Issue #16889 has been updated by mame (Yusuke Endoh).


Eregon (Benoit Daloze) wrote in #note-10:
> I do expect:
> ```
> TracePoint.new(:line) {|tp| p tp }.enable do
>   foo
> end
> ```
> to report lines within that last block, and within `foo`, so thread-local behavior in other words.
> So I'd want `tp.enable {}` to be like `tp.enable(target_thread: Thread.current) {}`.

Agreed. I think thread-local behavior is more reasonable. So, the current `target: :block` is not what you want, right?

Though I like thread-local behavior, I have some concerns:

* `tp.enable { Thread.new { foo }.join }` will not trace `foo` because it is run in another thread, but I'm unsure if this is expected.
* `tp.enable` called with no block should trace events in all threads, right? It is a bit inconsistent, but perhaps changing this to thread-local will break [Zeitwerk](https://github.com/fxn/zeitwerk/blob/243b43acde6f88893c2d02b191227c2917745a4f/test/lib/zeitwerk/test_ruby_compatibility.rb#L69-L70).


----------------------------------------
Feature #16889: TracePoint.enable { ... } also activates the TracePoint for other threads, even outside the block
https://bugs.ruby-lang.org/issues/16889#change-93423

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
----------------------------------------
```ruby
threads = []
inspects = []
trace = TracePoint.new(:line) do |tp|
  threads << Thread.current
  inspects << tp.inspect
end

done = false
thread = Thread.new do
  Thread.pass until done
end

trace.enable do
  line_event = true
  done = true
  sleep 1
end
thread.join

# Expected only within enable block (lines 14-16)
puts inspects

# Expected just 1
p threads.uniq
```

Results in:
```
$ ruby tpbug.rb
ruby tpbug.rb
#<TracePoint:line@tpbug.rb:14>
#<TracePoint:line@tpbug.rb:15>
#<TracePoint:line@tpbug.rb:16>
#<TracePoint:line@tpbug.rb:10>
[#<Thread:0x00005571134e3340 run>, #<Thread:0x00005571138ac828@tpbug.rb:9 dead>]
```

But I expected:
```
#<TracePoint:line@tpbug.rb:14>
#<TracePoint:line@tpbug.rb:15>
#<TracePoint:line@tpbug.rb:16>
[#<Thread:0x00005571134e3340 run>]
```

Because the RDoc says:
```
If a block is given, the trace will only be enabled within the scope of
the block.
```

For background I'm trying to improve the TracePoint specs in ruby/spec, but they are proving quite unreliable due to this.

@ko1 Thoughts?



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