[GHC] #13497: GHC does not use select()/poll() correctly on non-Linux platforms

[GHC]

#13497: GHC does not use select()/poll() correctly on non-Linux platforms
-------------------------------------+-------------------------------------
        Reporter:  nh2               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Runtime System    |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:  8684
 Related Tickets:  #8684, #12912     |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by nh2):

 I have pushed a workaround to my branch
 ​[https://github.com/ghc/ghc/compare/ghc-8.2.1-release...nh2:ghc-8.2.1
 -improve-fdRready-precision ghc-8.2.1-improve-fdRready-precision], namely
 commit
 [https://github.com/nh2/ghc/commit/1d037a16251751e98d4302f4be1e5659c3240958
 1d037a16].

 This completes my testing of my branch on Windows.

 I have tested the 4 of the 5 possible branches that `fdReady()` can take
 on Windows:

 1. Testing the `FILE_TYPE_PIPE` case suceeded with `ghc-bug-13497
 -accuracy-test.hs` (from
 [https://ghc.haskell.org/trac/ghc/ticket/13497#comment:18 comment 18]), by
 running it from the MSYS2 Mingw-w64 console (NOT `cmd.exe`!)
 2. Testing the `FILE_TYPE_DISK` case succeeded with the following file
 `ghc-bug-13497-windows-file-test.hs`:

     {{{
     import System.IO

     main = do
         writeFile "testfile" "hello"
         handle <- openFile "testfile" ReadMode
         hWaitForInput handle (5 * 1000)
     }}}

 3. Testing the `FILE_TYPE_CHAR` case suceeded by running `ghc-bug-13497
 -accuracy-test.hs` (see above) , but this time from `cmd.exe`. Here,
 focusing and unfocusing the Window triggers `EventType == FOCUS_EVENT` so
 that our loop is executed (I confirmed this with a print in the loop).
 4. Testing the `if (isSock)` case succeded with the echo server example
 given in the previous comment.
 5. I did not test the `default:` case
 ([https://github.com/nh2/ghc/blob/1d037a16251751e98d4302f4be1e5659c3240958/libraries/base/cbits/inputReady.c#L231
 this one]), because I don't know how to trigger it. There are 3 cases in
 which this branch could be taken according to the `GetFileType()`
 [https://msdn.microsoft.com/en-
 us/library/windows/desktop/aa364960(v=vs.85).aspx documentation]:
   A. `FILE_TYPE_REMOTE`, which seems impossible to create on modern
 Windows
   B. `FILE_TYPE_UNKNOWN`, for which it is literally unknown on how it can
 be created
   C. The very bottom of the `FILE_TYPE_PIPE` case, when `/* PeekNamedPipe
 didn't work - fall through to the general case */` happens. I don't know
 how to trigger this. Simon Marlow introduced this logic 9 years ago in
 commit
 [https://github.com/nh2/ghc/commit/1b0906e072344376ec7cb95afe314f2157b62b20
 1b0906e0], so maybe he knows.

 In any case, with this testing done I'm reasonably confident that my
 branch doesn't regress Windows.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13497#comment:25>
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