More detail would be helpful, but sounds like an infinite (Async?) thread. Try bracket (newStablePtr a) freeStablePtr (const $ wait a) +google to find out why. 2015-02-04 13:59 GMT+01:00 Magicloud Magiclouds < magicloud.magiclouds@gmail.com>:

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?

-- 竹密岂妨流水过 山高哪阻野云飞

And for G+, please use magiclouds#gmail.com.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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@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?

-- 竹密岂妨流水过 山高哪阻野云飞

And for G+, please use magiclouds#gmail.com.

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

Just found out that, the two functions of waitForEvent and waitForError cannot be run in "main" thread. I just forked them and used a getChar to block the program, and everything just went smooth. No idea what to proceed.... On Wed, Feb 4, 2015 at 8:59 PM, Magicloud Magiclouds < magicloud.magiclouds@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?

-- 竹密岂妨流水过 山高哪阻野云飞

And for G+, please use magiclouds#gmail.com.

-- 竹密岂妨流水过 山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.