em_posix_spawn_code.rb

          def self.instance
            @instance ||= begin
                            new.tap { |instance|
                              prev_handler = Signal.trap("CLD") {
                                if EM.reactor_running?
                                  EM.add_timer(0) { instance.signal }
                                end
                                prev_handler.call if prev_handler
                              }
                            }
                          end
          end

error_source.cpp

static EventMachine_t *EventMachine;

// ...

extern "C" void ensure_eventmachine (const char *caller = "unknown caller")
{
	if (!EventMachine) {
		const int err_size = 128;
		char err_string[err_size];
		snprintf (err_string, err_size, "eventmachine not initialized: %s", caller);
		#ifdef BUILD_FOR_RUBY
			rb_raise(rb_eRuntimeError, "%s", err_string);
		#else
			throw std::runtime_error (err_string);
		#endif
	}
}

stacktrace.txt

Running test 4009
ERROR!: eventmachine not initialized: evma_install_oneshot_timer
/home/mpage/.rbenv/versions/1.9.2-p180/lib/ruby/gems/1.9.1/bundler/gems/eventmachine-2806c630d863/lib/eventmachine.rb:375:in `add_oneshot_timer'
/home/mpage/.rbenv/versions/1.9.2-p180/lib/ruby/gems/1.9.1/bundler/gems/eventmachine-2806c630d863/lib/eventmachine.rb:375:in `add_timer'
/home/mpage/.rbenv/versions/1.9.2-p180/lib/ruby/gems/1.9.1/bundler/gems/common-3f6636fca4fc/em-posix-spawn/lib/em/posix/spawn/child.rb:100:in `block (2 levels) in instance'
/home/mpage/.rbenv/versions/1.9.2-p180/lib/ruby/gems/1.9.1/bundler/gems/eventmachine-2806c630d863/lib/eventmachine.rb:263:in `call'
/home/mpage/.rbenv/versions/1.9.2-p180/lib/ruby/gems/1.9.1/bundler/gems/eventmachine-2806c630d863/lib/eventmachine.rb:263:in `run'
iso_stress.rb:160:in `run'
iso_stress.rb:201:in `block in <main>'
iso_stress.rb:198:in `times'
iso_stress.rb:198:in `<main>'
iso_stress.rb: eventmachine not initialized: evma_install_oneshot_timer (RuntimeError)