https://stackoverflow.com/a/76399940

I would expect the following program to never produce duplicate numbers:

#include <stdio.h>
#include <pthread.h>
#include <unistd.h>

void *func (void *p)
{
  size_t count = 0;
  while (1)
    printf ("%zu\n", ++count);

  return NULL;
}

int main (void)
{
  pthread_t tid;
  pthread_create (&tid, NULL, func, NULL);
  usleep (1000);
  return 0;
}


But running it against ToT produces:
1
2
...
260
261
262
263
264
265
266
267
267   <<<--- bug
268
269
270
270   <<<--- bug
271

This appears to stem from commit 64f01020838

commit 64f01020838a382d833254297f650d4a55933bde
Author: Ulrich Drepper <drepper@redhat.com>
Date:   Mon Feb 9 20:08:44 2004 +0000

    (_IO_cleanup): Do not use locking when flushing the buffers.  Some thread might be using a stream.


Not sure what the motivation was -- surely delaying exit a bit for sake of correctness would be more appropriate here?