Calling exit inside a at_exit handler should not unwind or return

src/kernel.cr

@@ -117,22 +117,21 @@ end
 
 # :nodoc:
 module AtExitHandlers
-  class_getter? running = false
-
   def self.add(handler)
     handlers = @@handlers ||= [] of Int32 ->
     handlers << handler
   end
 
+  @@handler_iterator : Iterator(Int32 ->)?
+
   def self.run(status)
-    return status if running?
-    @@running = true
+    return status unless handlers = @@handlers
+
+    handler_iterator = @@handler_iterator ||= handlers.reverse_each
 
-    @@handlers.try &.reverse_each do |handler|
+    handler_iterator.each do |handler|
       begin
         handler.call status
-      rescue nested_exit : NestedExitError
-        status = nested_exit.status_code
       rescue handler_ex
         STDERR.puts "Error running at_exit handler: #{handler_ex}"
         status = 1 if status.zero?
@@ -165,22 +164,11 @@ def at_exit(&handler : Int32 ->) : Nil
   AtExitHandlers.add(handler)
 end
 
-class NestedExitError < Exception
-  getter status_code : Int32
-
-  def initialize(@status_code)
-  end
-end
-
 # Terminates execution immediately, returning the given status code
 # to the invoking environment.
 #
 # Registered `at_exit` procs are executed.
 def exit(status = 0) : NoReturn
-  if AtExitHandlers.running?
-    raise NestedExitError.new status
-  end
-
   status = AtExitHandlers.run status
   STDOUT.flush
   STDERR.flush