maximum execution time exceeded by fwrite method

Question

I am trying to write to some txt files using SplFileObject's fwrite method and getting below error message.

Fatal error: Maximum execution time of 30 seconds exceeded in /Users/oliverwilliams/Desktop/olliephp/directory.php on line 9.

Line 9 is while (!$textfile->eof()) { from the following code

$dir = new FilesystemIterator('garbagedirectory');
foreach ($dir as $file) {
    if ($file->getExtension() === 'txt') {
        $textfile = $file -> openFile('r+');
        while (!$textfile->eof()) {
            $textfile -> next();
        }
        $textfile->fwrite("This line was added dynamically");
    }
}

I am new to PHP. How get rid of that error?

This is the code I was emulating, from David Powers Lynda course. His code does work.

$docs = new FilesystemIterator('garbagedirectory');
foreach ($docs as $doc) {
if ($doc->getExtension() == 'txt') {
    $textfile = $doc->openFile('r+');
    $textfile->setFlags(SplFileObject::SKIP_EMPTY | SplFileObject::READ_AHEAD
    | SplFileObject::DROP_NEW_LINE);
    echo '<h2>' . $textfile->getFilename() . '</h2>';
    foreach ($textfile as $line) {
        echo "$line<br>";
    }
    $textfile->seek(3);
    echo '<br>';
    echo 'This is the fourth line: ' . $textfile->current();
    while(!$textfile->eof()) {
        $textfile->next();
    }
    $textfile->fwrite("\r\n\r\nThis line was added dynamically");
    }
    }