On Thu, Aug 6, 2009 at 12:17 PM, Simon Marlow
The SIGVTALRM signal is delivered to one (random) thread in the program, so I imagine it just isn't being delivered to the thread that runs your second call to sleep. (the main Haskell thread is a "bound thread" and hence gets an OS thread to itself).
In addition to my last e-mail - would you say that blocking SIGVTALRM in the thread that runs sleep (or poll etc.) is the right thing to do in order to avoid the problem of getting EINTR? E.g. for the main thread: {-# LANGUAGE ForeignFunctionInterface #-} module Main where import Foreign.C.Types import Control.Concurrent import System.Posix.Signals import Control.Monad blockSIGVTALRM :: IO () blockSIGVTALRM = addSignal virtualTimerExpired `liftM` getSignalMask >>= blockSignals >> return () sleep :: IO () sleep = blockSIGVTALRM >> c_sleep 3 >>= print main :: IO () main = sleep foreign import ccall safe "unistd.h sleep" c_sleep :: CUInt -> IO CUInt How much would the thread scheduling be affected by this? Many thanks, Levi