Hi, all. Say I have a function solve which is a constraint solver. It reconfigures its input to be a solution. If there is no solution, it returns the input. solve :: a -> Either a a solve input output = maybe (Left input) Right $ solve' input If there is a solution, it finds it in a few seconds. If there is no solution, it goes away for days proving that. So, I'd like to give up on it if it doesn't return in a few seconds. I can think of several ways of doing that. I could keep a tally of the number of variable assignments and give up when it reaches an impossibly huge number. I could change the type to a -> IO (Either a a ) and use getCPUTime. Is there a standard way to do this? Can you think of another way to do it? Cheers, David
Hi there,
On Sat, Sep 6, 2008 at 13:30, David F. Place
If there is a solution, it finds it in a few seconds. If there is no solution, it goes away for days proving that. So, I'd like to give up on it if it doesn't return in a few seconds. I can think of several ways of doing that. I could keep a tally of the number of variable assignments and give up when it reaches an impossibly huge number. I could change the type to a -> IO (Either a a ) and use getCPUTime.
Is there a standard way to do this? Can you think of another way to do it?
I don't know, but this seems relevant: http://www.haskell.org/pipermail/haskell-cafe/2005-October/011946.html I'd make a generic (i.e. higher-order) function that handles the timeout for any computation. i.e. timeout :: (a -> b) -> Int -> a -> IO (Maybe b) or similar. Arnar
a -> IO (Either a a ) and use getCPUTime.
Is there a standard way to do this? Can you think of another way to do it?
I don't know, but this seems relevant: http://www.haskell.org/pipermail/haskell-cafe/2005-October/011946.html
I'd make a generic (i.e. higher-order) function that handles the timeout for any computation. i.e.
timeout :: (a -> b) -> Int -> a -> IO (Maybe b)
http://haskell.org/ghc/docs/latest/html/libraries/base/System-Timeout Perhaps this is for not so much for pure computations as hanging when connecting to nonresponsive servers, although I also use it in a case where buggy long-running code could frustrate the responsiveness of unrelated processes.. --Lane
On 2008 Sep 6, at 7:30, David F. Place wrote:
Say I have a function solve which is a constraint solver. It reconfigures its input to be a solution. If there is no solution, it returns the input.
solve :: a -> Either a a solve input output = maybe (Left input) Right $ solve' input
If there is a solution, it finds it in a few seconds. If there is no solution, it goes away for days proving that. So, I'd like to give up on it if it doesn't return in a few seconds.
http://www.haskell.org/haskellwiki/Timing_out_computations -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
On Sat, 2008-09-06 at 11:10 -0400, Brandon S. Allbery KF8NH wrote:
On 2008 Sep 6, at 7:30, David F. Place wrote:
Say I have a function solve which is a constraint solver. It reconfigures its input to be a solution. If there is no solution, it returns the input.
solve :: a -> Either a a solve input output = maybe (Left input) Right $ solve' input
If there is a solution, it finds it in a few seconds. If there is no solution, it goes away for days proving that. So, I'd like to give up on it if it doesn't return in a few seconds.
Thanks, Arnar, Christopher and Brandon. I looked into all your suggestions. I came up with this: import Control.Exception import System.Timeout apt :: Int -> (a -> a) -> a -> IO (Either a a) apt time f x = do { ans <- timeout time $ evaluate (f x) ; return $ maybe (Left x) Right ans } test x = sum [1..x] test2 x = length $ repeat x Which seems to do what I want for test: *Main> apt 100 test 100 Right 5050 *Main> apt 100 test 1000 Right 500500 *Main> apt 100 test 10000 Right 50005000 *Main> apt 100 test 100000 Left 100000 *Main> apt 100 test 1000000 Left 1000000 *Main> apt 100 test 10000000 Left 10000000 But, the following sets the cpu spinning and can't be interrupted. *Main> apt 100 test2 100
On Sat, 2008-09-06 at 12:17 -0400, David F. Place wrote:
On Sat, 2008-09-06 at 11:10 -0400, Brandon S. Allbery KF8NH wrote:
On 2008 Sep 6, at 7:30, David F. Place wrote:
Say I have a function solve which is a constraint solver. It reconfigures its input to be a solution. If there is no solution, it returns the input.
solve :: a -> Either a a solve input output = maybe (Left input) Right $ solve' input
If there is a solution, it finds it in a few seconds. If there is no solution, it goes away for days proving that. So, I'd like to give up on it if it doesn't return in a few seconds.
Thanks, Arnar, Christopher and Brandon. I looked into all your suggestions.
I came up with this:
import Control.Exception import System.Timeout
apt :: Int -> (a -> a) -> a -> IO (Either a a) apt time f x = do { ans <- timeout time $ evaluate (f x) ; return $ maybe (Left x) Right ans }
test x = sum [1..x] test2 x = length $ repeat x
Which seems to do what I want for test:
*Main> apt 100 test 100 Right 5050 *Main> apt 100 test 1000 Right 500500 *Main> apt 100 test 10000 Right 50005000 *Main> apt 100 test 100000 Left 100000 *Main> apt 100 test 1000000 Left 1000000 *Main> apt 100 test 10000000 Left 10000000
But, the following sets the cpu spinning and can't be interrupted. *Main> apt 100 test2 100
length (repeat x) doesn't require allocating any memory. GHC only performs a context switch at heap checks. If there are no allocations, there are no heap checks and therefore no context switches.
participants (5)
-
Arnar Birgisson -
Brandon S. Allbery KF8NH -
Christopher Lane Hinson -
David F. Place -
Derek Elkins