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Re: Help debugging hang with epoll_engine
From: Daniel Miller <bonsaiviking () gmail com>
Date: Thu, 07 Jun 2012 15:55:05 -0500

Ok, I've narrowed it down to a loop in function "run" in nse_main.lua. The call to l_loop (socket.loop in Lua) happens on line 937. I ran nse_main.lua through luac -l to generate opcodes, so here's my best guess at the execution trace:

  OP_GETUPVAL OP_MOVE OP_CALL -- pairs(pending)
  OP_JMP OP_TFORCALL OP_TFORLOOP -- for co, thread in pairs(pending) do
    -- pending must be empty, because we move past it to:
  OP_GETUPVAL OP_LOADK OP_CALL -- collectgarbage "step"
OP_JMP -- end -- loop back to line 850, while
  OP_GETUPVAL OP_MOVE OP_CALL OP_TEST -- next running
    OP_GETUPVAL OP_MOVE OP_CALL OP_TEST -- next waiting
    OP_TEST -- threads_iter
    --false, so fal through to line 863
  OP_GETUPVAL OP_MOVE OP_CALL -- table_size
    --function table_size
    OP_LOADK -- local n=0
    OP_GETUPVAL OP_MOVE OP_CALL -- pairs(t)
    OP_JMP OP_TFORCALL OP_TFORLOOP -- for _ in pairs(t) do
    OP_RETURN -- return 0, since t was empty
  OP_GETUPVAL OP_MOVE OP_CALL -- table_size
    --function table_size
    OP_LOADK -- local n=0
    OP_GETUPVAL OP_MOVE OP_CALL -- pairs(t)
    OP_JMP OP_TFORCALL OP_TFORLOOP -- for _ in pairs(t) do
      OP_ADD -- n = n + 1
      OP_TFORCALL OP_TFORLOOP -- for _ in pairs(t) do
    OP_RETURN -- return 1
  -- back in run() at line 864
  OP_GETTABUP OP_CALL -- cnse.key_was_pressed()
    OP_TEST -- false, go to line 878
  OP_MOVE OP_LOADK OP_CALL -- elseif progress "mayBePrinted" then
    OP_TEST -- false, go to line 887
  OP_GETUPVAL OP_MOVE OP_CALL -- pairs(waiting)
  OP_JMP OP_TFORCALL OP_TFORLOOP -- for co, thread in pairs(waiting) do
    OP_SELF OP_CALL -- thread:timed_out() -- line 300
OP_GETTABLE OP_EQ OP_GETTABLE OP_EQ -- if self.type == "hostrule" or self.type == "portrule" then
        OP_GETTABUP OP_GETTABLE -- return cnse.timedOut(self.host);
        OP_TAILCALL
        OP_RETURN
    -- back in run() line 888
    OP_TEST -- false (not timed out)
    OP_TFORCALL OP_TFORLOOP -- for co, thread in pairs(waiting) do
  OP_GETUPVAL OP_MOVE OP_CALL -- pairs(running)
  OP_JMP OP_TFORCALL OP_TFORLOOP -- for co, thread in pairs(running) do
    -- No running threads
  OP_GETUPVAL OP_LOADK OP_CALL -- loop(50)
  Breakpoint 4, l_loop (L=0x8c56ad8) at nse_nsock.cc:401


So there is a problem where the thread is stuck in waiting state, and the socket won't timeout. I can't figure it out, and I need to move on to other things right now. I hope someone else can see what I can't.

Dan
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