Issue #10871 has been updated by Aaron Patterson.


I tried to fix this, but I can't figure it out. :(

I tried adding the singleton class to the stack frame.  Since the stack frames are thread local, I thought that would at least fix the problem, but it didn't.

Here is the patch I tried:

  https://gist.github.com/tenderlove/a8e30c1f764040de7536

I verified that `putspecialobject 2` would put the right class on the stack, and I verified that `m_core_define_method` got the right class, but still your test failed.  I don't understand what I'm doing wrong. :(

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Bug #10871: Sclass thread unsafe due to CREF sharing
https://bugs.ruby-lang.org/issues/10871#change-51593

* Author: Evan Phoenix
* Status: Open
* Priority: High
* Assignee: 
* ruby -v: 2.2.0p0, trunk
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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When entering an sclass, the context is tracked via the same cref mechanism used for class and module, specifically on the iseq->cref_stack. The bug is that the cref_stack is the wrong place to put the new cref because the scope is specific only to that sclass body. Mutating and using the iseq->cref_stack causes any code that reads the cref via this cref_stack to incorrectly pick up the sclass instance instead of the proper scope!

This is major thread safety bug because it means that all uses of `class << obj` are thread-unsafe and can cause random code to fail.

Here is a simple reproduction of the bug: https://gist.github.com/evanphx/6eef92f2c40662a4171b

I attempted to fix the bug by treating an sclass body the same as an eval, which already has special handling for cref's but I don't understand the code enough to make that change quickly.

I believe this is a major bug and hope that ruby-core can address it soon.

Thank you!



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