On 2/3/11 7:19 PM, Brandon S Allbery KF8NH wrote:
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On 2/3/11 19:16 , Brandon S Allbery KF8NH wrote:
POSIX FIFOs and GHC's nonblocking file descriptors implementation don't play well together; you should launch the writer end first and let it block
More specifically, I think what's happening here is that a non-blocking open() of a FIFO returns with the fd not actually open yet, a situation which isn't expected, and a blocking open will block until the other side is opened.
When opening the Fd[1], the program does block until the other end is opened by another process (verified via printf debugging). But I'll keep that in mind while digging around. I was aware of semi-closed handles, but not semi-open Fds. [1] Via (System.Posix.IO.openFd file System.Posix.IO.ReadOnly Nothing System.Posix.IO.defaultFileFlags). Unfortunately, if compiled under GHC <= 6.12.1 with -threaded, then openFd will always throw an error about the system call being interrupted by GHC's thread scheduling timer. This bug is fixed in unix-2.4.1.0 which, IIRC, requires GHC-7. The problem is that the earlier implementation of openFd uses throwErrnoPathIfMinus1, instead of throwErrnoPathIfMinus1Retry (which does not exist in base <= 4.3.0.0). Cf., http://www.haskell.org/pipermail/glasgow-haskell-users/2009-December/018147.... -- Live well, ~wren