<?php 
$file = fopen("test.txt","w+"); 
 
$t1 = microtime(TRUE); 
if (flock($file,LOCK_EX)) 
{ 
 sleep(10); 
 fwrite($file,"Write something"); 
 flock($file,LOCK_UN); 
 echo "Ok locking file!"; 
} 
else 
{ 
 echo "Error locking file!"; 
} 
 
fclose($file); 
 
$t2 = microtime(TRUE); 
echo sprintf("%.6f",($t2-$t1)); 

<?php 
$file = fopen("test.txt","a+"); 
 
$t1 = microtime(TRUE); 
if (flock($file,LOCK_EX|LOCK_NB)) 
{ 
 sleep(10); 
 fwrite($file,"Write something"); 
 flock($file,LOCK_UN); 
 echo "Ok locking file!"; 
} 
else 
{ 
 echo "Error locking file!"; 
} 
 
fclose($file); 
 
$t2 = microtime(TRUE); 
echo sprintf("%.6f",($t2-$t1));