[project @ 2005-05-06 00:30:56 by sof]

[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.

1 files changed, 1 insertions, 0 deletions

diff --git a/libraries/base/include/consUtils.h b/libraries/base/include/consUtils.h
index e6a04e87dc..953f5c7289 100644
--- a/libraries/base/include/consUtils.h
+++ b/libraries/base/include/consUtils.h
@@ -8,4 +8,5 @@
 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