On 11/17/05, Joel Reymont
On Nov 17, 2005, at 1:44 PM, Sebastian Sylvan wrote:
Are you sure it's safe to kill a thread which has already been killed?
It seems so from the docs.
Why do you fork off the killing of the threads? Why not just run them in sequence?
Someone said that they read somewhere that killThread can block. I'm not gonna point any fingers at musasabi ;-).
Also, I'd recommend refactoring the code a bit, write a function "parIO" which runs IO computations in parallell and then define timeout in terms of that.
I did this by stealing the timeout/either combinators from the Asynchronous Exceptions paper. It did not help a single bit.
This is somewhat frustrating for me because I had a very similar (if not the exact same) issue when writing some test applications for an FMOD binding. However, all that source code (and so much more) was lost due to a hard disk failure. I am now struggling to remember what was the cause, and how I solved. What I do remember is that the timeout and parIO functions in the concurrent programming papers I found were NOT correct. killThread did NOT behave as expected when I killed an already killed thread. I tried multiple tricks here (including some which required recursive do-notation) to try to get the parIO function to only kill the *other* thread. This could be done by having the two spawned threads take their computations in an MVar along with the threadID of the other thread. something like: parIO f1 f2 = do m <- newEmptyMVar -- result Mvar mf1 <- newEmptyMVar -- MVar for f1 mf2 <- newEmptyMVar -- MVar for f2 -- fork worker threads t1 <- forkIO (child m mf1) t2 <- forkIO (child m mf2) -- pass computations and threadID to worker threads putMVar mf1 (t2, f1) putMVar mf2 (t1, f2) -- return result takeMVar m where child m mf = do (tid, f) <- takeMVar mf x <- f putMVar m x killThread tid timeout t f = threadDelay (round (t * 1e6)) `parIO` f As I remember another solution I came up with was to wrap the "child" function body in a catch statement. The child function was just a helper function that ran a computation and put its result in an MVar. I *think* the problem *may* have been that when an FFI function got "ThreadKilled" exception asynchrounously that got bubbled up to the parIO thread for some reason. /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862