Bug #17302: The TracePoint API does not allow setting multiple line traces within the same method (ISEQ)

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.6: REQUIRED, 2.7: REQUIRED, 3.0: DONTNEED, 3.1: DONTNEED

[[e-mail] (Liran Haimovitch)]

While setting a tracepoint for a line for the second time within a method, the first one turns off.

I believe this is because the encoded_iseq_trace_instrument function resets the trace value of an instruction rather than just turning it on if needed: https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3178

And it is unconditionally called, not limited to the correct line: https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3219

[[e-mail] (Liran Haimovitch)]

• File my_test.rb my_test.rb added

[e-mail] (Liran Haimovitch) wrote:

When setting a second line tracepoint within a method the first one will be turned off.

I believe this is due to the fact that the encoded_iseq_trace_instrument function resets the trace value of an instruction rather then just turn it on if needed - https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3178

And it is unconditionally called, not limited to the correct line: https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3219

Attaching a short file to reproduce the bug, based on the existing enable_spec.rb in the Ruby repo.

[[e-mail] (Liran Haimovitch)]

[e-mail] (Liran Haimovitch) wrote in #note-1:

[e-mail] (Liran Haimovitch) wrote:

When setting a second line tracepoint within a method the first one will be turned off.

I believe this is due to the fact that the encoded_iseq_trace_instrument function resets the trace value of an instruction rather then just turn it on if needed - https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3178

And it is unconditionally called, not limited to the correct line: https://github.com/ruby/ruby/blob/799253dc46e96518687dcd4fdca42582251ccffe/iseq.c#L3219

Attaching a short file to reproduce the bug, based on the existing enable_spec.rb in the Ruby repo.

After some additional investigation, it seems that when adding multiple breakpoints to the same method (ISEQ) only the last one will apply. BUT, if I disable even one of them, all the breakpoints that are left enabled will work simultaneously.

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[ko1 (Koichi Sasada)]

• Status changed from Open to Closed

Applied in changeset git|084e7e31b257f6ac859769553b4c1c6ca2930152.

---

remain enabled and line specified trace points

If two or more tracepoints enabled with the same target and with
different target lines, the only last line is activated.
This patch fixes this issue by remaining existing trace instructions.
[Bug #17302]

[Eregon (Benoit Daloze)]

• Related to Bug #18646: Inconsistent behavior for the targeted TracePoints in ruby 2.6-2.7 and 3+ added

[Eregon (Benoit Daloze)]

• Backport changed from 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN to 2.6: REQUIRED, 2.7: REQUIRED, 3.0: DONTNEED, 3.1: DONTNEED

[Eregon (Benoit Daloze)]

Backport was requested in https://bugs.ruby-lang.org/issues/18646, and I adjusted the Backport field for it.