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

Ryan Yates fryguybob at gmail.com
Thu Feb 5 03:42:38 UTC 2015

When you get the "thread blocked indefinitely in an STM transaction" it is
the result of the garbage collector finding no references to the TVars that
a 'retry'ing or blocked transaction.  If there are no references to those
TVars then there is no way for that transaction to ever succeed.  I don't
know if that helps.

On Wed, Feb 4, 2015 at 7:59 AM, Magicloud Magiclouds <
magicloud.magiclouds at gmail.com> wrote:

> 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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