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Date: Mon, 14 Jul 2025 11:18:17 +0900
To: cygwin AT cygwin DOT com
Subject: Re: Problems with flushing stdin in mintty
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From: Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Sun, 13 Jul 2025 20:34:56 +0900
Takashi Yano wrote:
> On Sun, 13 Jul 2025 11:40:10 +0200
> Christoph Reiter wrote:
> > I'm having the problem that under cygwin flushing stdin for some reason doesn't
> > work when running in mintty. It works when running cygwin in the Windows
> > terminal though. In my case the program using this is pacman, where it asks
> > various questions and if you hit some keys in-between questions they leak into
> > the next one, resulting in invalid input.
> > 
> > Example program showing the problem. Type some text in the first 5 seconds, and
> > see the input leak into the next input. Any ideas/workarounds welcome.
> > 
> > ```c
> > // gcc -o flush_stdin flush_stdin.c
> > #include <stdio.h>
> > #include <unistd.h>
> > #include <termios.h>
> > 
> > int main() {
> >     printf("type something in the next 5 secs\n");
> >     for (int i=0; i < 5; i++) {
> >         sleep(1);
> >         printf("%d\n", i);
> >     }
> > 
> >     // Flush stdin
> >     int fd = fileno(stdin);
> >     if (fd != -1) {
> >         printf("flushing stdin\n");
> >         if (tcflush(fd, TCIFLUSH) == -1) {  // this doesn't seem to do anything
> >             perror("Error flushing stdin");
> >             return 1;
> >         }
> >     } else {
> >         perror("Error getting file descriptor for stdin");
> >         return 1;
> >     }
> > 
> >     char buffer[100];
> >     printf("Enter some text:\n");
> >     fgets(buffer, sizeof(buffer), stdin);
> >     printf("You entered: %s\n", buffer);
> > 
> >     return 0;
> > }
> > ```
> 
> Thanks for the report.
> 
> This seems to be a bug of pty code. If you enter 'return' key
> in the first 5 sec, the input will be flushed.
> 
> I'll look into that.

Fixed.
https://cygwin.com/pipermail/cygwin-patches/2025q3/014128.html

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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