When the key doesn't exist it may return either bool(false) or int(0) (I get different return values on different servers), so be careful if you check for something like ($memcache->increment($key) === false).
(PECL memcache >= 0.2.0)
Memcache::increment — Increment item's value
$value= 1 ] )
Memcache::increment() increments value of an item by
value. If item specified by
key was not numeric and cannot be converted to a
number, it will change its value to
Memcache::increment() does not
create an item if it doesn't already exist.
Also you can use memcache_increment() function.
Do not use Memcache::increment() with items that have been stored compressed because subsequent calls to Memcache::get() will fail.
Key of the item to increment.
Increment the item by
Returns new items value on success Im Fehlerfall wird
Beispiel #1 Memcache::increment() example
/* procedural API */
$memcache_obj = memcache_connect('memcache_host', 11211);
/* increment counter by 2 */
$current_value = memcache_increment($memcache_obj, 'counter', 2);
/* OO API */
$memcache_obj = new Memcache;
/* increment counter by 3 */
$current_value = $memcache_obj->increment('counter', 3);
Be careful to use Memcache::decrement() and never Memcache::increment() with a negative value.
The check that prevents Memcache::decrement() from going negative is not in place with Memcache::increment(), so you can end up with a garbage integer on the order of 18 quintillion stored in place of the expected value.
Instead of checking the value before incrementing, you can simply ADD it instead before incrementing each time. If it's already there, your ADD is ignored, and if it's not there, it's set.
If you add($memcacheKey, 0) and then increment($memcacheKey, 1) in that order, you avoid all possible race conditions. If two threads are running this code concurrently, you will always end up with your value being 2 no matter which order the threads execute in.
If the key does not exist, memcache does NOT return false (as you might expect) but 0.
You won't get any hint that the key did not exist and still does not exist and that nothing was incremented.