On Sun, Oct 24, 2004 at 02:16:50PM +0200, Peter Simons wrote:
Tomasz Zielonka writes:
AFAIK, Handles have finalisers which close them, but I don't know if GHC triggers garbage collection when file descriptors run out. If not, you will have problems if you manage to run out of fds between GCs.
Thank you for answering.
Now there is only one problem: Assuming I could _not_ use 'bracket', 'withFile', 'finally' or any of the other usual scope-guarding techniques, what would I do? (The handle has to be passed up to the outside of the scope in which it was opened.) Refactoring comes to the mind... ;)
If I stored the handle in an 'MVar' and attached an MVar-finalizer to that, would that work better? Would the MVar's finalizer be run any sooner than the one attached to the handle anyway? Both are just finalizers, so it won't make any difference AFAICS.
Or can I explicitly trigger garbage collection somehow? Say, in case I receive an exception telling me that file descriptors are running out? Which exception would I even get in this case?
Peter
You could try using something like this instead of the normal openFile: (or make it even less portable by importing GHC.IOBase and only retrying on ResourceExhausted) module Main where import IO import System.Mem myOpenFile path mode = catch (openFile path mode) $ \_ -> do putStrLn "==> Open failed. Retrying <==" performGC openFile path mode open = openFile "/tmp/foo" ReadMode myOpen = myOpenFile "/tmp/foo" ReadMode Example: -- Let's eat all available filedescriptors. *Main> sequence (repeat open) Loading package haskell98 ... linking ... done. *** Exception: /tmp/foo: openFile: resource exhausted (Too many open files) -- They are indeed all gone. *Main> h <- open *** Exception: /tmp/foo: openFile: resource exhausted (Too many open files) -- What about performing garbage collection? *Main> h <- myOpen ==> Open failed. Retrying <== *Main> h {handle: /tmp/foo} *Main> Groeten, Remi -- Nobody can be exactly like me. Even I have trouble doing it.