synchronized keyword in singleton

[radkat]

Good day, all.

I'm new to multi-thread and cannot emulate this issue properly, so if anyone could help by comment, I would appreciate much.

The question is, whether synchronized keyword is needed in non-static methods of singleton ?

E.g.

public class MySingleton {
private static MySingleton instance;

public static synchronized MySingleton getInstance() {
if (instance == null) {
instance = new MySingleton();
}
return instance;
}

public void myMethod() {
// do something
}
}

Does method myMethod need to be synchronized or not ?

[vadimf]

Yes, it's needed, singleton's instance can be accessed from different threads at time.

[christiaan_se]

Hi,
it depends. The synchronized is not needed to guarantee that your singleton is indeed a singleton. That's what the synchronized on the static method getInstance() is for. If your myMethod() performs something that should be thread safe, you should make it synchronized.

kind regards,
Christiaan

[puredanger]

You may find my article on Singleton construction, double-checked locking, etc of interest.

Alex Miller - Pure Danger Tech