[ruby-core:80791] [Ruby trunk Feature#13483] TracePoint#enable with block for thread-local trace

Issue #13483 has been reported by ko1 (Koichi Sasada).

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Feature #13483: TracePoint#enable with block for thread-local trace
https://bugs.ruby-lang.org/issues/13483

* Author: ko1 (Koichi Sasada)
* Status: Open
* Priority: Normal
* Assignee: ko1 (Koichi Sasada)
* Target version: 2.5
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# Summary

`TracePoint#enable` with block should enable thread-local trace.

# Current behavior

`TracePoint#enable` enables TracePoint for all of threads, even if it called with `do...end` blcok.

```
t1 = Thread.new{
  loop{
    x = 1
  }
}
th = nil
trace = TracePoint.new(:line){|tp|
  if th != Thread.current
    p th = Thread.current
  end
}

trace.enable do
  loop{
    a = 1
    b = 2
  }
end
```

This program shows both main thread and thread `t1` hooked by line events.

# Problem

However, usually `trace.enable do ... end` imply the programmer want to enable hooks only for this block, not for other threads.
For example, Ruby's test for TracePoint skips hooks on other threads.
https://github.com/ruby/ruby/blob/trunk/test/ruby/test_settracefunc.rb#L620

# Proposal

`TracePoint#enable` with block should enable thread-local trace.
I believe proposed behavior is easy to use.

# Consideration

(1) It breaks backward compatibility. Is it acceptable?
(2) What happen on created threads? Should inherit thread-local hooks or ignore them?

I want to ask users of TracePoint.

Thanks,
Koichi



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