[ruby-core:111921] [Ruby master Bug#18518] NoMemoryError + [FATAL] failed to allocate memory for twice 1 << large

Issue #18518 has been updated by mame (Yusuke Endoh).


Discussed at the dev meeting.

Are there any real-world use cases (other than rubyspec) where you would like to prohibit `integer << large`?

@matz was initially positive about prohibiting huge object generation as early failure. However, there was little reason to prohibit only `Integer#<<`, so he considered to prohibit any Bignum generation larger than a threshold size, such as Integer#*.
However, there was little reason to prohibit only Bignum, so he wanted that Array and String should be prohibited from generating objects larger than the threshold size.
However, we sometimes use File.read with a file larger than 2GB. We reached that it would be difficult to determine a reasonable size threshold. The discussion ran out of time here.

----------------------------------------
Bug #18518: NoMemoryError + [FATAL] failed to allocate memory for twice 1 << large
https://bugs.ruby-lang.org/issues/18518#change-101344

* Author: Eregon (Benoit Daloze)
* Status: Rejected
* Priority: Normal
* ruby -v: ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
* Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
Repro:
```ruby
exp = 2**40 # also fails with bignum e.g. 2**64

def exc
  begin
    yield
  rescue NoMemoryError => e
    p :NoMemoryError
  end
end

p exp
exc { (1 << exp) }
exc { (-1 << exp) }
exc { (bignum_value << exp) }
exc { (-bignum_value << exp) }
```

Output:
```
$ ruby -v mri_oom.rb
ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
mri_oom.rb:7: warning: assigned but unused variable - e
1099511627776
:NoMemoryError
[FATAL] failed to allocate memory
```

3.1.0 seems fine:
```
$ ruby -v mri_oom.rb
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-linux]
mri_oom.rb:7: warning: assigned but unused variable - e
1099511627776
:NoMemoryError
:NoMemoryError
:NoMemoryError
:NoMemoryError
```



-- 
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