Project

General

Profile

Actions

Bug #13239

closed

Bug with "special exceptions" when they are thrown in context of a rescue clause.

Added by nvashchenko (Nikolay Vashchenko) about 7 years ago. Updated about 6 years ago.

Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
2.4.x, 2.3.x, etc
[ruby-core:79641]

Description

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:

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

Actions

Also available in: Atom PDF

Like0
Like0Like0Like0Like0Like0Like0Like0Like0