Add a test and @tmm1s patch for making post-fork EM.run calls work as…

… expected.

Closes eventmachine#213

lib/eventmachine.rb

@@ -155,7 +155,13 @@ def self.run blk=nil, tail=nil, &block
     # will start without release_machine being called and will immediately throw
 
     #
-
+    if reactor_running? and @reactor_pid != Process.pid
+      # Reactor was started in a different parent, meaning we have forked.
+      # Clean up reactor state so a new reactor boots up in this child.
+      stop_event_loop
+      release_machine
+      @reactor_running = false
+    end
 
     tail and @tails.unshift(tail)
 
@@ -169,6 +175,7 @@ def self.run blk=nil, tail=nil, &block
       @next_tick_queue ||= []
       @tails ||= []
       begin
+        @reactor_pid = Process.pid
         @reactor_running = true
         initialize_event_machine
         (b = blk || block) and add_timer(0, b)
@@ -252,7 +259,7 @@ def self.fork_reactor &block
       if self.reactor_running?
         self.stop_event_loop
         self.release_machine
-        self.instance_variable_set( '@reactor_running', false )
+        @reactor_running = false
       end
       self.run block
     end

tests/test_basic.rb

@@ -245,4 +245,28 @@ def c.unbind
     assert !timer_ran
     assert_equal 1, num_close_scheduled
   end
+
+  def test_fork_safe
+    return unless cpid = fork { exit! } rescue false
+
+    read, write = IO.pipe
+    EM.run do
+      cpid = fork do
+        write.puts "forked"
+        EM.run do
+          EM.next_tick do
+            write.puts "EM ran"
+            exit!
+          end
+        end
+      end
+      EM.stop
+    end
+    Process.waitall
+    assert_equal "forked\n", read.readline
+    assert_equal "EM ran\n", read.readline
+  ensure
+    read.close rescue nil
+    write.close rescue nil
+  end
 end