Bug #13239
Updated by nobu (Nobuyoshi Nakada) about 7 years ago
I've stumbled upon a case when ruby is supposed to throw "IOError: stream closed"(https://github.com/ruby/ruby/blob/trunk/thread.c#L4823) because there was a retained FD lock by another thread, but I'm was getting this instead of it: ``` RuntimeError: can't modify frozen IOError /home/vagrant/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/puma-3.6.2/lib/puma/server.rb:877:in `write' /home/vagrant/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/puma-3.6.2/lib/puma/server.rb:877:in `<<' /home/vagrant/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/puma-3.6.2/lib/puma/server.rb:877:in `stop' ``` I've done some digging and it appeared to a be a ruby bug with how such exceptions(so called "special exceptions") are handled. This exception is being frozen right after creation: https://github.com/ruby/ruby/blob/trunk/vm.c#L2078 but later, when it's thrown, it's being handled exactly as regular exception that is not frozen, which leads to a problem here: https://github.com/ruby/ruby/blob/trunk/eval.c#L511 - it is an attempt to assign the "#cause" attribute on it when it all happens inside a rescue clause, since the exception itself is frozen. I've created a script to reproduce it: ```ruby ``` rd, wr = IO.pipe Thread.new do IO.select [rd] wr.close end begin raise 'any exception' rescue wr << 'A' end ``` It works with this ruby fork where I've added sleep for couple of seconds to imitate slow system call response, to keep the FD locked for a while and produce initial exception: https://github.com/ruby/ruby/blob/trunk/eval.c#L511