cvs commit: fptools/libraries/base/GHC ConsoleHandler.hs fptools/libraries/base/cbits consUtils.c fptools/libraries/base/include consUtils.h fptools/ghc/compiler/ghci InteractiveUI.hs

[Krasimir Angelov]

Hi Sigbjorn,

The workaround breaks another useful feature of GHC. You can't spawn
GHCi through runInteractiveProcess anymore. You should use
flushConsole only if the stdin is console handle.

Cheers,
  Krasimir

On 5/6/05, Sigbjorn Finne <sof at haskell.org> wrote:
> sof         2005/05/05 17:30:58 PDT
> 
>  Modified files:
>    libraries/base/GHC   ConsoleHandler.hs
>    libraries/base/cbits consUtils.c
>    libraries/base/include consUtils.h
>    ghc/compiler/ghci    InteractiveUI.hs
>  Log:
>  [mingw only]
>  Work around bug in win32 Console API which showed up in the GHCi UI:
>  if the user typed in characters prior to the appearance of the prompt,
>  the first of these characters always came out as a 'g'. The GHCi UI does
>  for good reasons one-character reads from 'stdin', which causes the
>  underlying APIs to become confused. A simple repro case is the following
>  piece of C code:
> 
>  /*----------------------*/
>  #include <stdio.h>
>  #include <windows.h>
>  int main()
>  {
>      char ch1,ch2;
>      HANDLE hStdIn = GetStdHandle(STD_INPUT_HANDLE);
>      DWORD dw;
> 
>      /* Type in some characters before the prompt appears and be amused.. */
>      sleep(1000); printf("? ");
>      ReadConsoleA(hStdIn,&ch1,1,&dw,NULL);
>      ReadConsoleA(hStdIn,&ch2,1,&dw,NULL);
>  /*  or, if you want to use libc:
>      read(0,&ch1,1); read(0,&ch2,1); */
> 
>      printf("%c%c\n", ch1,ch2);
>      return 0;
>  }
>  /*----------------------*/
> 
>  This happens across win32 OSes, and I can't see anything untoward as far
>  as API usage goes (the GHC IO implementation uses read(), but that
>  reduces to ReadConsoleA() calls.) People inside the Behemoth might want
>  to have a closer look at this..
> 
>  Not much we can do about this except work around the problem by flushing
>  the input buffer prior to reading from stdin. Not ideal, as type-ahead
>  is a useful feature. Flushing is handled by GHC.ConsoleHandler.flushConsole
> 
>  Merge to STABLE.
> 
>  Revision  Changes    Path
>  1.8       +13 -0     fptools/libraries/base/GHC/ConsoleHandler.hs
>  1.5       +13 -0     fptools/libraries/base/cbits/consUtils.c
>  1.2       +1 -0      fptools/libraries/base/include/consUtils.h
>  1.203     +9 -0      fptools/ghc/compiler/ghci/InteractiveUI.hs
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