Using on MacOS / iOS - semTrywait: invalid argument (Bad file descriptor)

[epoberezkin]

Hello!

Is MacOS/iOS supported?

I have:

test = do
  sem <- semOpen "/test" OpenSemFlags {semCreate = True, semExclusive = False} stdFileMode 1
  semThreadWait sem
  semPost sem

It fails on semThreadWait:

uncaught exception: IOException of type InvalidArgument
semTrywait: invalid argument (Bad file descriptor)

#43 suggests it might not be working on MacOS?

Thank you!

[hasufell]

We'll probably have to mark this function as unsupported operation like in other cases, such as

{-# WARNING semOpen
    "operation will throw 'IOError' \"unsupported operation\" (CPP guard: @#if HAVE_FDATASYNC@)" #-}

So you see this warning at compile time and at runtime simply get an io error.

But I'm not sure yet that this is really unsupported.

[hasufell]

Can you try this patch:

--- a/System/Posix/Semaphore.hsc
+++ b/System/Posix/Semaphore.hsc
@@ -1,4 +1,5 @@
 {-# LANGUAGE Safe #-}
+{-# LANGUAGE CApiFFI #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  System.Posix.Semaphore
@@ -110,18 +111,18 @@ semGetValue_ sem ptr = do throwErrnoIfMinus1Retry_ "semGetValue" $
                           cint <- peek ptr
                           return $ fromEnum cint

-foreign import ccall safe "sem_open"
+foreign import capi safe "semaphore.h sem_open"
         sem_open :: CString -> CInt -> CMode -> CUInt -> IO (Ptr ())
-foreign import ccall safe "sem_close"
+foreign import capi safe "semaphore.h sem_close"
         sem_close :: Ptr () -> IO CInt
-foreign import ccall safe "sem_unlink"
+foreign import capi safe "semaphore.h sem_unlink"
         sem_unlink :: CString -> IO CInt

-foreign import ccall safe "sem_wait"
+foreign import capi safe "semaphore.h sem_wait"
         sem_wait :: Ptr () -> IO CInt
-foreign import ccall safe "sem_trywait"
+foreign import capi safe "semaphore.h sem_trywait"
         sem_trywait :: Ptr () -> IO CInt
-foreign import ccall safe "sem_post"
+foreign import capi safe "semaphore.h sem_post"
         sem_post :: Ptr () -> IO CInt
-foreign import ccall safe "sem_getvalue"
+foreign import capi safe "semaphore.h sem_getvalue"
         sem_getvalue :: Ptr () -> Ptr CInt -> IO Int

[hasufell]

I can reproduce it and with my patch above, it seems to work.

So this appears to be another instance of: https://www.haskell.org/ghc/blog/20210709-capi-usage.html and #110 (comment)