Re: Slightly OT: non-buffered stdin in Java

On Thu, Jun 8, 2023 at 11:23 PM Paul Procacci <pprocacci@gmail.com> wrote:
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>
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> On Thu, Jun 8, 2023 at 10:55 PM Aryeh Friedman <aryeh.friedman@gmail.com> wrote:
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>> On Thu, Jun 8, 2023 at 10:32 PM Paul Procacci <pprocacci@gmail.com> wrote:
>> >
>> >
>> >
>> > On Thu, Jun 8, 2023 at 9:22 PM Aryeh Friedman <aryeh.friedman@gmail.com> wrote:
>> >>
>> >> 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
>> >>
>> >
>> > stdbuf only works for stdio buffering of which read(2) and write(2) aren't.
>>
>> I also tried it with System.in.read() in Java and it was also buffered
>> but according to the openjdk source it appears that this is on
>> purpose.
>>
>>
>>
>> --
>> Aryeh M. Friedman, Lead Developer, http://www.PetiteCloud.org
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>
>
> When you just `./a.out` you're being bitten by the tty.
> You can manipulate that terminal to do what you want.  Start reading termios(4).
>
> Without a tty you will only get a character at a time with the following:
>
> #include <unistd.h>
>
> int main(int argc, char **argv)
> {
>   char ch;
>   for(;;){
>     ssize_t r = read(0,&ch,1);
>     if(!r) break;
>     write(1, &ch, 1);
>   }
>   _exit(0);
> }

Please see the whole context the goal is to make it so I can type at
the command line into a java program and have instantaneous
presentation of any characters I enter to Java



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