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);
}

run the above script by two php processes.

Handle race condition. In my case, the cache file won't change frequently, so read it until the data is what we want. You can think it as spinlock. it may execute 1-10 times(more if better IO) till the data is ready. if you got better solution, let me know please, send me an email.
Read Time-of-check_to_time-of-use for why there is a race condition,

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);
}