Re: Slightly OT: non-buffered stdin in Java
- Reply: Greg Lewis : "Re: Slightly OT: non-buffered stdin in Java"
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Date: Fri, 09 Jun 2023 03:35:52 UTC
On Thu, Jun 8, 2023 at 11:23 PM Paul Procacci <pprocacci@gmail.com> wrote: > > > > On Thu, Jun 8, 2023 at 10:55 PM Aryeh Friedman <aryeh.friedman@gmail.com> wrote: >> >> 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 > > > > 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