[ruby-core:103351] [Ruby master Feature#17762] A simple way to trace object allocation

Issue #17762 has been updated by Eregon (Benoit Daloze).


byroot (Jean Boussier) wrote in #note-15:
> I understand the concern. A `require` always seem more harmless than a method call. But being able to enable tracing with a require allow to enable it without modifying the code through: `RUBYOPT='-r objspace/tracing'`, which is in my opinion very valuable.

It's too bad `-e` is not allowed in RUBYOPT, otherwise one could do something like this:
```
RUBYOPT="-robjspace -eObjectSpace.trace_object_allocations_start" ruby ...
```
(or a shorter method to start it of course)

Maybe that would be useful to allow?

----------------------------------------
Feature #17762: A simple way to trace object allocation
https://bugs.ruby-lang.org/issues/17762#change-91442

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
----------------------------------------
How about having a short hand to `ObjectSpace.trace_object_allocations_start`, `ObjectSpace.allocation_sourcefile` and `ObjectSpace.allocation_sourceline`?

They are a very powerful tool for debugging and code-reading which allows us to identify an allocation site of an object.
Though they are never lightweight, they are the last resort when you try debugging code written by someone else.

However, the names are too long for me to remember and to type. Whenever I want to use them, I have to google, copy and paste the names.

## Proposal

To enable trace allocations:

```
require "objspace/trace" #=> objspace/trace is enabled
```

To show the allocation site of an object:

```
p obj #=> #<Object:0x...> @ (file.rb):(lineno)
```

## Example

```
require "objspace/trace"
require "active_support/all"

p ActiveSupport::VERSION::STRING
  #=> "6.1.3.1" @ /home/mame/work/ruby/local/lib/ruby/gems/3.1.0/gems/activesupport-6.1.3.1/lib/active_support/gem_version.rb:15
```

## Discussion

I've attached a simple patch that is originally authored by @ko1 .

* Is the message `objspace/trace is enabled` needed or not?
* To stop the trace, you need to use `ObjectSpace.trace_object_allocations_stop`. But, I guess that it is rare that we need to stop it during debugging.
* Is it too radical to redefine `Kernel#p`? I think that it is good enough for many cases. When it matters, the original APIs (`ObjectSpace.trace_object_allocations_start`, ...) can be used.

---Files--------------------------------
objspace-trace.patch (631 Bytes)


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