[ruby-core:127027] [Ruby Bug#15599] Mixing autoload and require causes deadlock and incomplete definition.

9 Oct 2026

      Issue #15599 has been updated by mame (Yusuke Endoh).

Status changed from Closed to Open

This issue is not fixed. The M:N thread scheduler seems to have only changed the timing. Adding `sleep` makes each result deterministic (confirmed on 3.3.8, 3.4.4, 4.0.2, and master).

i) shows `[:a1]`

```
$ cat a.rb
class A
  def a1() end
end

$ cat base.rb
autoload :A, './a'

t1 = Thread.new { p A.instance_methods(false) }
t2 = Thread.new { sleep 0.1; require './a' }

t1.join
t2.join

$ ruby base.rb
[:a1]
```

ii) shows `[]`

```
$ cat a.rb
class A
  sleep 0.2
  def a1() end
end

$ cat base.rb
autoload :A, './a'

t1 = Thread.new { sleep 0.1; p A.instance_methods(false) }
t2 = Thread.new { require './a' }

t1.join
t2.join

$ ruby base.rb
[]
```

iii) deadlocks

```
$ cat a.rb
sleep 0.2
class A
  def a1() end
end

$ cat base.rb
autoload :A, './a'

t1 = Thread.new { sleep 0.1; p A.instance_methods(false) }
t2 = Thread.new { require './a' }

t1.join
t2.join

$ ruby base.rb
base.rb:6:in 'Thread#join': No live threads left. Deadlock? (fatal)
```

The only difference among these is where `sleep` is inserted.

Let me reopen this.

----------------------------------------
Bug #15599: Mixing autoload and require causes deadlock and incomplete definition.
https://bugs.ruby-lang.org/issues/15599#change-119423

* Author: akr (Akira Tanaka)
* Status: Open
* ruby -v: ruby 2.7.0dev (2019-02-11 trunk 67049) [x86_64-linux]
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN
----------------------------------------
I found that mixing autoload and require causes deadlock and incomplete definition.

```
% cat a.rb 
class A
  def a1() end
end
% cat base.rb 
autoload :A, './a'

t1 = Thread.new { p A.instance_methods(false) }
t2 = Thread.new { require './a' }

t1.join
t2.join
% ruby base.rb 
Traceback (most recent call last):
	1: from base.rb:6:in `<main>'
base.rb:6:in `join': No live threads left. Deadlock? (fatal)
3 threads, 3 sleeps current:0x000055cc6943fde0 main thread:0x000055cc6935f4b0
* #<Thread:0x000055cc6938f190 sleep_forever>
   rb_thread_t:0x000055cc6935f4b0 native:0x00007f58d256eb40 int:0
   base.rb:6:in `join'
   base.rb:6:in `<main>'
* #<Thread:0x000055cc6968cfc8@base.rb:3 sleep_forever>
   rb_thread_t:0x000055cc69736180 native:0x00007f58ce7b3700 int:0 mutex:0x000055cc6943fde0 cond:1
    depended by: tb_thread_id:0x000055cc6935f4b0
   /home/akr/ruby/o0/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
   /home/akr/ruby/o0/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
   base.rb:3:in `block in <main>'
* #<Thread:0x000055cc6968ccd0@base.rb:4 sleep_forever>
   rb_thread_t:0x000055cc6943fde0 native:0x00007f58ce5b1700 int:0
   /tmp/a/a.rb:1:in `<top (required)>'
   /home/akr/ruby/o0/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
   /home/akr/ruby/o0/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
   base.rb:4:in `block in <main>'
% ruby base.rb
[:a1]
% ruby base.rb
[]
```

The last run which prints [] means incomplete definition of A which a1 method is not defined.

-- 
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