PHP synchronized file read write - php

Question

i am using the function write_php_ini to write files
see the accepted answer with around 40 upvotes at:
create ini file, write values in PHP
originally i was copying from here:
How to read and write to an ini file with PHP
from the answer that is not accepted, because they looked so similar
the problem is, what if 2 process write to it at the same time? (that is, the second post seems to handle it, whereas the first one does not)
how to avoid this problem?
this is the code:
public static function write_ini_file($assoc_arr, $path, $has_sections=FALSE) {
$content = "";
if ($has_sections) {
foreach ($assoc_arr as $key=>$elem) {
$content .= "[".$key."]\n";
foreach ($elem as $key2=>$elem2) {
if(is_array($elem2))
{
for($i=0;$i<count($elem2);$i++)
{
$content .= $key2."[] = \"".$elem2[$i]."\"\n";
}
}
else if($elem2=="") $content .= $key2." = \n";
else $content .= $key2." = \"".$elem2."\"\n";
}
}
}
else {
foreach ($assoc_arr as $key=>$elem) {
if(is_array($elem))
{
for($i=0;$i<count($elem);$i++)
{
$content .= $key."[] = \"".$elem[$i]."\"\n";
}
}
else if($elem=="") $content .= $key." = \n";
else $content .= $key." = \"".$elem."\"\n";
}
}
if (!$handle = fopen($path, 'w')) {
return false;
}
$success = fwrite($handle, $content);
fclose($handle);
return $success;
}