note 109237 modified in function.flock by danbrown

I just spent some time (again) to understand why a reading with file_get_contents() and file was returning me an empty string "" or array() whereas the file was existing and the contents not empty.

In fact, i was locking file when writing it (file_put_contents third arg) but not testing if file was locked when reading it (and the file was accessed a lot).

So, please pay attention that file_get_contents(), file() and maybe others php files functions are going to return empty data like if the contents of the file was an empty string.

To avoid this problem, you have to set a LOCK_SH on your file before reading it (and then waiting if locked).

Something like this :

<?php
public static function getContents($path, $waitIfLocked = true) {
	if(!file_exists($path)) {
		throw new Exception('File "'.$path.'" does not exists');
	}
	else {
		$fo = fopen($path, 'r');
		$locked = flock($fo, LOCK_SH, $waitIfLocked);
		
		if(!$locked) {
			return false;
		}
		else {
			$cts = file_get_contents($path);
			
			flock($fo, LOCK_UN);
			fclose($fo);
			
			return $cts;
		}
	}
}
?>

Code to test by yourself :

abc.txt :
someText

file.php :
<?php
$fo = fopen('abc.txt', 'r+');

flock($fo, LOCK_EX);
sleep(10);
flock($fo, LOCK_UN);
?>

file2.php : 
<?php
var_dump(file_get_contents('abc.txt'));
var_dump(file('abc.txt'));
?>

Then launch file.php and switch to file2.php during the 10 seconds and see the difference before/after --was-- I just spent some time (again) to understand why a reading with file_get_contents() and file was returning me an empty string "" or array() whereas the file was existing and the contents not empty. In fact, i was locking file when writing it (file_put_contents third arg) but not testing if file was locked when reading it (and the file was accessed a lot). So, please pay attention that file_get_contents(), file() and maybe others php files functions are going to return empty data like if the contents of the file was an empty string. To avoid this problem, you have to set a LOCK_SH on your file before reading it (and then waiting if locked). Something like this : public static function getContents($path, $waitIfLocked = true) { if(!file_exists($path)) { throw new Exception('File "'.$path.'" does not exists'); } else { $fo = fopen($path, 'r'); $locked = flock($fo, LOCK_SH, $waitIfLocked); if(!$locked) { return false; } else { $cts = file_get_contents($path); flock($fo, LOCK_UN); fclose($fo); return $cts; } } } Code to test by yourself : abc.txt : someText file.php : $fo = fopen('abc.txt', 'r+'); flock($fo, LOCK_EX); sleep(10); flock($fo, LOCK_UN); file2.php : var_dump(file_get_contents('abc.txt')); var_dump(file('abc.txt')); Then launch file.php and switch to file2.php during the 10 seconds and see the difference before/after http://php.net/manual/en/function.flock.php