import os
import time
import sys

dest_fname = 'DEST.txt'

# Print only once
has_printed = False
for i in range(100000):
    try:
        print("BE", time.time())

        fd = os.open(dest_fname, os.O_RDONLY)
        try:
            print("IN", time.time())
            content = os.read(fd, 1024)
            print("AF", time.time())

            try:
                assert content == b'CONTENT', 'FOUND INSTEAD: {}'.format(content)
            except AssertionError:
                print('ER1', fd, os.fstat(fd), file=sys.stderr)
                print('Exists:', os.path.exists(dest_fname), file=sys.stderr)
                raise
            else:
                if not has_printed:
                    print('OK-', fd, os.fstat(fd), file=sys.stderr)
                    has_printed = True

        finally:
            os.close(fd)
        print(i, content)
    except FileNotFoundError:
        print(i, ">> DELETED <<")
        # Recreate the file
        time.sleep(0.001) # Wait a bit
        fd = os.open(dest_fname, os.O_WRONLY|os.O_CREAT, 0o644)
        try:
            body = b"CONTENT"
            os.write(fd, body)
        finally:
            os.close(fd)

print("READ DONE.", file=sys.stderr)