When getSize return 0, after fwrtite, You must use clearstatcache:
$tmpFile = new \SplFileObject('/tmp/file.txt');
$fp = $tmpFile->openFile('w');
$fp->fwrite('123');
$fp->fflush();
echo $fp->getSize(); //Return 0
clearstatcache();
echo $fp->getSize(); //Return 3
https://bugs.php.net/bug.php?id=72182