多线程写文件排它锁

<?php
    $fp = fopen("/tmp/lock.txt","w+");
    if(flock($fp, LOCK_EX)){// 进行排它型锁定
        fwrite($fp,"Write something here\n");
        flock($fp, LOCK_UN);// 释放锁定
    }else{
        echo "Couldn't lock the file !";
    }
    fclose($fp);
?>