[Haskell-cafe] How does RTS judge that a STM transaction is blocked?

[Magicloud Magiclouds]

Hi,

  I met an issue while I was using xhb. When a certain property of root
window being changed, it was supposed to give me an AccessError. But
actually I got "thread blocked indefinitely in an STM transaction" when I
waitForEvent.

  AFAIK, in xhb, it forks a thread to read what X server sends. Then parse
and put it into a TChan. waitForEvent reads from the TChan.

  It is reasonable to me that if X server did not send anything, then
waitForEvent would be blocked. But apparently there are some other policies
in RTS.

  So what is that? And how should I debug it?

-- 
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