如何对数组使用增量？

Question

I know that it's possible to do something like that:

$wgMemc->set( $key, 2, 60*30 );
$wgMemc->incr( $key );

but what if the numeric value is inside an array, like this?:

$wgMemc->set( $key, array( 'enabled' => $row->enabled, 'disabled' => 0 ), 60*30 );
$wgMemc->incr( ??? );

what is the best way to rave the same behaviour?

Answer 1

You have to implement your own way of doing this. Idea is simple: 1) Get the value by key 2) Make necessary updates to it (Increment, decrement, anything) 3) Set the new value for the key

However If you are in a concurrent environment (like any publicly available script) then between 1 and 3 someone else can access this part of your code. Resulting in a simultaneous data updates. This could end badly for you

So We have to make sure that only single user/process/thread is updating data at the moment. We can use locks for this.

Instead of

$wgMemc->set( $key, array( 'enabled' => $row->enabled, 'disabled' => 0 ), 60*30 );
$wgMemc->incr( ??? );

let's add some locks there

// acuire lock
$lock      = false;
$lock_ttl  = 10;
$tries     = 0;
$max_tries = 500;

// trying to obtain the lock. If we can't "add" the key - it means
// that someone else is updating data at the moment
// so we'll wait
while ( $tries < $max_tries && !($lock = $wgMemc->add("lock_" . $key, 1, $lock_ttl)) ) {
    $tries++;
    usleep( 100 * ($tries % ($max_tries/10)) );
}

// check if we successfully obtained the lock and then do our stuff
if ($lock) {
    $data = $wgMemc->get( $key );
    // update our data
    $data['enabled'] = 1;
    $data['blablabla']++;
    $wgMemc->set( $key, $data, 60*30 );
}

// release lock
$wgMemc->delete("lock_" . $key);