schedule the starting time of events as accurately as possible - real-time

Question

I would like to schedule a series of events such that to about the nearest 5ms, the starting time of event N is t0 + dt*N, where t0 is some arbitrary time after the process starts. If the events were output to a terminal, they would occur regularly without pauses or speedups. If they were noises, it would produce a regular rhythm. This is my first attempt.
#include <stdio.h>
#include <time.h>
#include <math.h>
void fsleep(double t)
{
time_t sec = floor(t);
long nsec = 1e9*(t - sec);
struct timespec s;
s.tv_sec = sec;
s.tv_nsec = nsec;
nanosleep(&s, NULL);
}
int main(int argc, const char **argv)
{
for (unsigned i = 0;; i++) {
printf("%d\n", i);
fflush(stdout);
fsleep(0.334);
}
}
It is total garbage, even at realtime priority (nice -n -20). There are noticeable jitters the entire time, with pauses of up to 1 second, after which a whole bunch of numbers are printed in a row. To test whether it was my terminal, I made the following script:
from time import sleep
from sys import stdin
def raw_stdin():
"""Switches stdin to a non-buffering, non-echoing mode,
handing keystrokes directly to the program as soon as they're
received and printing nothing to the terminal."""
import termios as t
f = t.tcgetattr(stdin)
f[3] &= ~(t.ICANON|t.ECHO)
t.tcsetattr(stdin, t.TCSANOW, f)
raw_stdin()
for i in range(10000000):
#sleep(.334)
stdin.read(1)
print(i)
If I hit any key regularly, i.e. with the same time intervals between strokes down to the nearest 10ms or so, I get regular outputs, with zero hesitations. This proves the terminal is more than responsive enough, and that what I'm trying to do is possible. I have a hard time imagining the computer can't do something I can do with my left index finger.
I think it might have something to do with my linux kernel. I'd be interested to know what happens if this is run in windows, or on other linux kernels.

Answer 1

I figured it out. It was my terminal all along (xfce4-terminal). There's a bug in it that messes up realtime output. See https://stackoverflow.com/a/47744798/1840698 for more.