Re: Slightly OT: non-buffered stdin in Java

On Thu, Jun 8, 2023 at 6:37 PM Dr. Nikolaus Klepp <dr.klepp@gmx.at> wrote:
>
> Anno domini 2023 Thu, 8 Jun 17:22:38 -0400
>  Aryeh Friedman scripsit:
> > On Thu, Jun 8, 2023 at 2:39 PM Dr. Nikolaus Klepp <dr.klepp@gmx.at> wrote:
> > >
> > > Anno domini 2023 Thu, 8 Jun 14:01:19 -0400
> > >  Aryeh Friedman scripsit:
> > > > Under Java stdin (System.in) is a buffered stream not sent to the
> > > > application until return is pressed.  But, Java can read from
> > > > files/sockets and other generic InputStreams unbuffered.   So I was
> > > > wondering if there is a command that will make stdin go to a file so
> > > > that Java can open that file and read it unbuffered?
> > > >
> > > > I know I can do something like cat ->file but that makes it hard to
> > > > sync stdout and stderr (both are unbuffered in Java) with the file
> > > > version of stdin
> > > >
> > >
> > > "stdbuf" might be what you look for:
> > >
> > > https://man.freebsd.org/cgi/man.cgi?query=stdbuf
> >
> > Will likely need to play with it more but stdbuf -i 0 -o 0 cat -|cat
> > didn't produce the expected immediate echo I still had to hit return
> >
>
> Your console is linebuffered, so "cat" receives lines. IIRC "cat" disables linebuffer on input by itself, so you should use someting else for testing.
>
> Nik
>

I am pretty convinced by the following test it is not working as advertised:

aryehl@neomarx:~/Desktop % cat foo.c
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

int main()
{
    int in=fcntl(STDIN_FILENO, F_DUPFD, 0);
    int out=fcntl(STDOUT_FILENO, F_DUPFD, 0);
    char c=0;

    do {
        read(in,&c,1);
        write(out,&c,1);
    } while(c!=EOF);
}
aryehl@neomarx:~/Desktop % !cc
cc foo.c
aryehl@neomarx:~/Desktop % stdbuf -i 0 -o 0 ./a.out
this is not echoing!
this is not echoing!
neither is this
neither is this
^C
aryehl@neomarx:~/Desktop %

-- 
Aryeh M. Friedman, Lead Developer, http://www.PetiteCloud.org