Re: [Haskell-cafe] Preventing leaked open file descriptors when catching exceptions

FYI, lsof confirms that there are indeed many many open connections to the same FIFO: Is there some other way to get at (and clean up) the file descriptor that is left by System.Posix.IO.openFD after it throws an exception? PingPipes 25115 rrnewton 124r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 125r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 126r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 127r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 128r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 129r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 130r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 131r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 132r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 133r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 134r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 135r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 136r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 137r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 PingPipes 25115 rrnewton 138r FIFO 8,2 0t0 25166171 /tmp/pipe_9083984821255795683 On Tue, Feb 21, 2012 at 11:13 AM, Ryan Newton wrote:

Hi all,

I'm trying to run a loop that repeatedly attempts to open a file until it succeeds. The file is a named pipe in nonblocking mode, so the writer can only connect after the reader has connected. (Perhaps there is some way to determine this by stat'ing the pipe, but I don't know it yet.)

Thus I do something like the following:

tryUntilNoIOErr $ do performGC -- The reader must connect first, the writer here spins with backoff. PIO.openFd filename PIO.WriteOnly Nothing fileFlags

I'm running GC between iterations to try to make sure I get rid of open files. Also, in the "tryUntilNoIOErr" code below I have some debugging messages which indicate that ioeGetHandle reports no handles associated with the exceptions I'm getting back. (If there were handles provided I could close them explicitly.)

In spite of these attempted precautions I'm seeing "too many open files" exceptions in simple benchmarks that should only have a maximum of ONE file open.

Any hints / pointers?

Thanks, -Ryan

mkBackoff :: IO (IO ()) mkBackoff = do tref <- newIORef 1 return$ do t <- readIORef tref writeIORef tref (min maxwait (2 * t)) threadDelay t where maxwait = 50 * 1000

tryUntilNoIOErr :: IO a -> IO a tryUntilNoIOErr action = mkBackoff >>= loop where loop bkoff = handle (\ (e :: IOException) -> do bkoff BSS.hPutStr stderr$ BSS.pack$ " got IO err: " ++ show e case ioeGetHandle e of Nothing -> BSS.hPutStrLn stderr$ BSS.pack$ " no hndl io err." Just x -> BSS.hPutStrLn stderr$ BSS.pack$ " HNDL on io err!" ++ show x loop bkoff) $ action