[Haskell-cafe] How to send signal from Xmonad to my app?

[Magicloud Magiclouds]

Hi,
  I have a little program, which shows a message box when gets 'USR1'
signal. This works fine when I `kill -USR1 $PID`.
  But my code in xmonad.hs does not work. No error throws out. And as
I inspected, the "pid" is right. Only nothing happened in my app. So I
wonder what is wrong?

28                                      , ((mod4Mask, xK_x),
sendSignal2PIDinFile sigUSR1 ".sidebar.pid")

31 sendSignal2PIDinFile signal pidfile = io $ do
32   pid <- readFile pidfile
33   signalProcess signal $ read pid

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