[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.
( Handler(..)
, installHandler
, ConsoleEvent(..)
+ , flushConsole
) where
{-
import Foreign
import Foreign.C
+import GHC.IOBase
+import GHC.Handle
data Handler
= Default
rts_installHandler :: CInt -> Ptr (StablePtr (CInt -> IO ())) -> IO CInt
foreign import ccall unsafe "RtsExternal.h rts_ConsoleHandlerDone"
rts_ConsoleHandlerDone :: CInt -> IO ()
+
+
+flushConsole :: Handle -> IO ()
+flushConsole h =
+ wantReadableHandle "flushConsole" h $ \ h_ ->
+ throwErrnoIfMinus1Retry_ "flushConsole"
+ (flush_console_fd (fromIntegral (haFD h_)))
+
+foreign import ccall unsafe "consUtils.h flush_input_console__"
+ flush_console_fd :: CInt -> IO CInt
#endif /* mingw32_HOST_OS */
return -1;
}
+int
+flush_input_console__(int fd)
+{
+ HANDLE h;
+ if ( (h = (HANDLE)_get_osfhandle(fd)) != INVALID_HANDLE_VALUE ) {
+ if ( FlushConsoleInputBuffer(h) ) {
+ return 0;
+ }
+ }
+ /* ToDo: translate GetLastError() into something errno-friendly */
+ return -1;
+}
+
#endif /* defined(mingw32_HOST_OS) || ... */
extern int set_console_buffering__(int fd, int cooked);
extern int set_console_echo__(int fd, int on);
extern int get_console_echo__(int fd);
+extern int flush_input_console__ (int fd);
#endif