Question

I have this piece of code below as shown .
Our Application runs on 5 web servers controlled by a Load Balancer ,all connecting to one Memcache instance .

I guess that this piece of synchrnozation works only for one Instance .

Please let me know how can i synchrnoze this piece of code when 5 web servers are trying to access the Memcache

public class Memcache {
    private MemcachedClient memclient = null;  
    private static Memcache instance = null;

    public static Memcache getInstance() {
        if (instance == null) {
            try {
                synchronized (Memcache.class) {
                    instance = new Memcache();
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return instance;
    }

    private Memcache() throws IOException {
        MemcachedClientBuilder builder = new XMemcachedClientBuilder();
        memclient = builder.build();

    }

}

Answer 1

Why not initialize it like this?

private static Memcache instance = new Memcache();

Bare in mind that what you tried to achieve at the synchronization here is problematic,
As two threads might pass the (if (instance == null) (a context switch might be after that line)
So you can consider the double check pattern,
BUt at some version of java there is a problem with it.
At the link I provided , there is info about problem, and
in this link, you can read about Singleton with the volatile keyword.

I still would go for the option I suggested above.