[ruby-core:70403] [Ruby trunk - Bug #11448] [Open] Requiring a given library may take 23x longer depending on `require` context

Issue #11448 has been reported by Rafa=C3=ABl Blais Masson.

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Bug #11448: Requiring a given library may take 23x longer depending on `req=
uire` context
https://bugs.ruby-lang.org/issues/11448

* Author: Rafa=C3=ABl Blais Masson
* Status: Open
* Priority: Normal
* Assignee:=20
* ruby -v: ruby 2.2.2p95 (2015-04-13 revision 50295) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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I was trying to narrow down the longest things to require during Rails boot=
 when I stumbled on this.

Add two lines in `securerandom.rb` in order to output the time taken to `re=
quire 'openssl'`:

~~~
 # -*- coding: us-ascii -*-
 begin
+  start =3D Time.now
   require 'openssl'
+  puts Time.now - start
 rescue LoadError
 end

 # =3D=3D Secure random number generator interface.
 # ...
~~~

Now run a script containing just this:

~~~
require 'securerandom'
~~~

Average output: `0.038829`

But run a similar script that requires a higher-level library, like:

~~~
require 'action_mailer'
~~~

Average output: `0.907959`

This still measures the time taken to `require 'openssl'` only. Why is it 2=
3x times slower? Because it is nested within other `require` calls? When re=
quiring `action_mailer`, this is the tree of files required to get to `secu=
rerandom`:

~~~
require 'action_mailer'
  require 'abstract_controller'
    require 'active_support/rails'
      require 'active_support/deprecation'
        require 'active_support/deprecation/behaviors'
          require 'active_support/notifications'
            require 'active_support/notifications/instrumenter'
              require 'securerandom'
~~~

When starting one level down, time to `require 'openssl'` is cut in half:

~~~
require 'abstract_controller'
~~~

Average output: `0.465274`



--=20
https://bugs.ruby-lang.org/