Your code may be suffering from a race condition.
Mid way through, you re-open the file in w mode, which truncates the file to zero length. If another copy of your script opens and attempts to read the file while it's been truncated but before it's been read, the counter will be reset to zero.
Here is an updated version of your code:
$filename = 'content/general_site_data/total_site_page_loads.txt';
// Open our file in append-or-create mode.
$fh = fopen($filename, "a+");
if(!$fh)
die("unable to create file");
// Before doing anything else, get an exclusive lock on the file.
// This will prevent anybody else from reading or writing to it.
flock($fh, LOCK_EX);
// Place the pointer at the start of the file.
fseek($fh, 0);
// Read one line from the file, then increment the number.
// There should only ever be one line.
$total_site_page_loads = 1 + intval(trim(fgets($fh)));
// Now we can reset the pointer again, and truncate the file to zero length.
fseek($fh, 0);
ftruncate($fh, 0);
// Now we can write out our line.
fwrite($fh, $total_site_page_loads . "\n");
// And we're done. Closing the file will also release the lock.
fclose($fh);
echo '------------------------------',
'<br />Site Wide Page Views: ',
$total_site_page_loads,
'<br />';
Because the initial open is in append-or-create mode, you don't need to handle a case where the file doesn't exist, unless the initial open failed.
With the file locking in place, this code should never reset the counter in the file, no matter how many concurrent requests there are. (Unless you happen to also have other code writing to the file, of course.)
