On 29 November 2005 06:29, Tomasz Zielonka wrote:
On Mon, Nov 28, 2005 at 11:27:46PM +0000, Joel Reymont wrote:
Folks,
How would you implement a timed read from a channel with STM? I would like to return Timeout if nothing was read from a TChan in X ms.
Is this a basic two-thread timeout implementation or is there a more elegant way of implementing this using `orElse`?
Here is a basic two-thread implementation:
http://www.haskell.org/pipermail/haskell-cafe/2005-January/008303.html
The other approach I see is to create a TVar that would be updated with current time every 0.1 s (or something like that), but that would be rather inefficient.
You could also create a time-out manager thread (with a priority queue, etc), so you don't have to spawn a thread for every timeout.
Interestingly, GHC already has a timeout thread - the I/O manager thread handles threadDelay too. It wouldn't be too hard to adapt it to do STM timeouts too, with a function like registerTimeout :: Int -> STM (TVar Bool) and you wait for your timeout by waiting for the TVar to contain True. Cheers, Simon