Re: Slightly OT: non-buffered stdin in Java

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