https://github.com/actix/actix-webreddit 上面感觉每一两个月都会有 actix 关于 unsafe issue/pr 跟作者吵架的帖子。这次又是，没过两天，结果昨天作者发推：
https://twitter.com/fafhrd91/status/1218135374339301378
I am done with open source.
reddit 上面有人总结的事件经过：
TLDR:
<unknown> commented: The following code is unsound:
https://github.com/actix/actix-net/blob/7c5fa25b23a802b27e8066caf4e01e3c2cedeb35/actix-service/src/cell.rs#L34-L36
This uses Rc::as_ref() to obtain a reference to the underlying data, which does not guarantee uniqueness. It is possible to obtain several mutable references to the same memory location by calling this function repeatedly:
let mycell = Cell::new(vec![1,2,3]); let ref1 = mysell.get_mut(); let ref2 = mysell.get_mut(); // obtained a second mutable reference; UB starts here
This may lead to arbitrary memory errors triggered from safe code, the most common of which would be use-after-free. These two references do not need to exist in the same function to trigger undefined behavior, they only need to exist at the same point in time.
A proper way to implement Cell:get_mut() would be calling Rc::get_mut() which guarantees uniqueness instead of Rc::as_ref().
fafhrd91 commented: This is internal code. There is no repeated call to get_mut() anywhere in code
fafhrd91 commented: Please, don’t start
Shnatsel commented: These two references do not need to exist in the same function to trigger undefined behavior, they only need to exist at the same point in time.
An easy way to see if this is a problem in practice is replace .as_ref() with .get_mut().unwrap() and see if anything panics.
cdbattags commented: @fafhrd91, I don't think "unsound" was meant to be personal or offensive.
Why close this so quickly?
fafhrd91 commented: I need unit test that shows UB.
...
fafhrd91 commented: this patch is boring
CJKay commented: So is resolving silent data corruption.
bbqsrc commented: @fafhrd91 seriously? Please just stop writing Rust. You do not respect semver, you do not respect soundness, so why are you using a language predominantly based around doing these things right?
JohnTitor commented: @bbqsrc I understand your point, but that doesn't mean you should use offensive words.
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