[#111712] [Ruby master Feature#19322] Support spawning "private" child processes — "kjtsanaktsidis (KJ Tsanaktsidis) via ruby-core" <ruby-core@...>
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14 messages
2023/01/07
[ruby-core:111920] [Ruby master Feature#18285] NoMethodError#message uses a lot of CPU/is really expensive to call
From:
"mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date:
2023-01-20 05:41:43 UTC
List:
ruby-core #111920
Issue #18285 has been updated by mame (Yusuke Endoh).
Discussed at the dev meeting. @matz is positive about the change and said h=
e would give it a try. The message format is slightly changed as follows:
* If the receiver is a Class, `... for class <class name>` should be printe=
d.
* If the receiver is a Module, `... for module <module name>` should be pri=
nted.
* If the receiver is an extended object (i.e., has a singleton class), `any=
_to_s` should be used.
* Otherwise, `... for an instance of <class name>` should be printed.
Examples:
```
42.time #=3D> undefined method `time' for an instance of Integer (NoMeth=
odError)
class Foo
privatee #=3D> undefined local variable or method 'privatee' for class Fo=
o (NoMethodError)
end
def (o=3DObject.new).foo
end
o.bar #=3D> undefined method `bar' for #<Object: 0xdeadbeef(any_to_s)>=
(NoMethodError)
```
I'll update my PR later. When we use the new message format and find it inc=
onvenient, we will adjust it accordingly.
----------------------------------------
Feature #18285: NoMethodError#message uses a lot of CPU/is really expensive=
to call
https://bugs.ruby-lang.org/issues/18285#change-101343
* Author: ivoanjo (Ivo Anjo)
* Status: Open
* Priority: Normal
----------------------------------------
Hello there! I'm working at Datadog on the ddtrace gem -- https://github.co=
m/DataDog/dd-trace-rb and we ran into this issue on one of our internal tes=
ting applications. I also blogged about this issue in <https://ivoanjo.me/b=
log/2021/11/01/nomethoderror-ruby-cost/>.
### Background
While testing an application that threw a lot of `NoMethodError`s in a Rail=
s controller (this was used for validation), we discovered that service per=
formance was very much impacted when we were logging these exceptions. Whil=
e investigating with a profiler, the performance impact was caused by calls=
to `NoMethodError#message`, because this Rails controller had a quite comp=
lex `#inspect` method, that was getting called every time we tried to get t=
he `#message` from the exception.
### How to reproduce
```ruby
require 'bundler/inline'
gemfile do
source 'https://rubygems.org'
gem 'benchmark-ips'
end
puts RUBY_DESCRIPTION
class GemInformation
# ...
def get_no_method_error
method_does_not_exist
rescue =3D> e
e
end
def get_runtime_error
raise 'Another Error'
rescue =3D> e
e
end
def inspect # <-- expensive method gets called when calling NoMethodError=
#message
Gem::Specification._all.inspect
end
end
NO_METHOD_ERROR_INSTANCE =3D GemInformation.new.get_no_method_error
RUNTIME_ERROR_INSTANCE =3D GemInformation.new.get_runtime_error
Benchmark.ips do |x|
x.config(:time =3D> 5, :warmup =3D> 2)
x.report("no method error message cost") { NO_METHOD_ERROR_INSTANCE.messa=
ge }
x.report("runtime error message cost") { RUNTIME_ERROR_INSTANCE.message }
x.compare!
end
```
### Expectation and result
Getting the `#message` from a `NoMethodError` should be no costly than gett=
ing it from any other exception.
In reality:
```
ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]
no method error message cost
115.390 (=B1 1.7%) i/s - 580.000 in 5.027822s
runtime error message cost
6.938M (=B1 0.5%) i/s - 35.334M in 5.092617s
Comparison:
runtime error message cost: 6938381.6 i/s
no method error message cost: 115.4 i/s - 60130.02x (=B1 0.00) slower
```
### Suggested solutions
1. Do not call `#inspect` on the object on which the method was not found (=
see <https://github.com/ruby/ruby/blob/e0915ba67964d843832148aeca29a1f8244c=
a7b1/error.c#L1962>)
2. Cache result of calling `#message` after the first call. Ideally this sh=
ould be done together with suggestion 1.
--=20
https://bugs.ruby-lang.org/
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