php-save-load-using-require-method-race condition-demo

gistfile1.txt

<?php

$cachePath = '/tmp/t.php';

$put = function($cachePath){
    $code = '<?php';
    $code .= "\n\n";
    $code .= 'return ' . var_export([], true) . ';';
    file_put_contents($cachePath, $code, LOCK_EX);
};

$get = function($cachePath) {
    return require($cachePath);
};


$retry = function($cachePath) use($get) {
    $start = microtime (true);

    $count = 0;
    do {
        $result = $get($cachePath);
        // Race condition happens when $result is not array.
        if (is_array($result)) {
            if ($count >0) {
              echo sprintf("%s => %s micro seconds".PHP_EOL, $count, (microtime(true) - $start) * 1000000);
            }
          
            return $result;
        }
        $count++;
    } while($result === 1 );
};

$load = function($cachePath) use($retry, $put) {
    $put($cachePath); // Create the file every time, so we can see the race condition exists

    return $retry($cachePath);
};

for($i=0;$i<1000000;$i++) {
    $load($cachePath);
}

The loop woule take 22 micro seconds , which is acceptable in my case, but a better solution is to diable the truncation problem, check here

New way

<?php

$cachePath = '/tmp/t.php';

$put = function($cachePath){
    $code = '<?php';
    $code .= "\n\n";
    $code .= 'return ' . var_export([], true) . ';';

    $fp = fopen($cachePath, "c");

    flock($fp, LOCK_EX);
    fwrite($fp, $code);

    fclose($fp);
};

$get = function($cachePath) {
    return require($cachePath);
};

$load = function($cachePath) use($get, $put) {
    $put($cachePath); // Create the file every time, so we can see the race condition exists

    var_dump($get($cachePath));
};

for($i=0;$i<1000000;$i++) {
    $load($cachePath);
}