Timeout::ExitException can be raised by nested timeouts

[trogd0r]

Behavior

Nested timeout blocks can result in a Timeout::ExitException being raised, rather than a Timeout::Error

How to reproduce

The below will sometimes raise a Timeout::ExitException, sometimes a Timeout::Error (roughly 50/50).
  

begin
  Timeout.timeout(2) do
    Timeout.timeout(2) do
      sleep 3
    end
  end
rescue Exception => e
  puts "raised a #{e.class}"
end

Cause (maybe)

Hacking up the Timeout module as follows:

module Timeout
  class Error
    def self.handle_timeout(message) # :nodoc:
      exc = ExitException.new(message)

      begin
        puts "yield #{exc.object_id} (#{message})"
        yield exc
      rescue ExitException => e
        puts "test #{e.object_id} vs #{exc.object_id} => #{exc.equal?(e)} (#{message})"
        raise new(message) if exc.equal?(e)
        puts "re-raise #{e.object_id}('#{e}') (#{message})"
        raise
      end
    end
  end
end

Timeout.timeout(2, nil, "outer timeout") do
  Timeout.timeout(2, nil, "inner timeout") do
    sleep 3
  end
end

shows that, when an ExitException is raised, the "inner" exception is being caught by the "outer" handle_timeout block. Suspicious this is the result of indeterminate Thread#raise behavior?

Environment

Ruby 3.3.5
Timeout 0.4.1
Ubuntu 24.04.1 running on WSL2

[eregon]

It sounds somewhat related to https://bugs.ruby-lang.org/issues/20314
I'll try to think about a fix when I have some time.

[hsbt]

FYI: ruby/ruby#10851

[sergio-bobillier]

👋 We are experiencing this issue in our setup. But our experiments show that this only happens if both timeout calls have the same timeout value, for example the following test:

RSpec.describe 'Timeout' do
  it 'times out' do
    expect do
      Timeout.timeout(2) do
        Timeout.timeout(2) do
          sleep 19
        end
      end
    end.to raise_error(Timeout::Error)
  end
end

Fails all the time with a Timeout::ExitException that RSpec is not able to rescue:

Failures:

  1) Timeout times out
     Failure/Error: output.__send__(method, *args, &block)

     Timeout::ExitException:
       execution expired
     # Backtrace omitted ...
     #
     #   Showing full backtrace because every line was filtered out.
     #   See docs for RSpec::Configuration#backtrace_exclusion_patterns and
     #   RSpec::Configuration#backtrace_inclusion_patterns for more information.

Finished in 2.01 seconds (files took 0.13324 seconds to load)
2 examples, 1 failure

However, doing this change:

       Timeout.timeout(2) do
-        Timeout.timeout(2) do
+        Timeout.timeout(2.1) do
           sleep 19

Makes the test pass 100% of the time:

.

Finished in 2.01 seconds (files took 0.1275 seconds to load)
1 example, 0 failures