notify listener inside or outside inner synchronization
- by Jary Zeels
Hello all,
I am struggling with a decision. I am writing a thread-safe library/API. Listeners can be registered, so the client is notified when something interesting happens. Which of the two implementations is most common?
class MyModule {
protected Listener listener;
protected void somethingHappens() {
synchronized(this) {
... do useful stuff ...
listener.notify();
}
}
}
or
class MyModule {
protected Listener listener;
protected void somethingHappens() {
Listener l = null;
synchronized(this) {
... do useful stuff ...
l = listener;
}
l.notify();
}
}
In the first implementation, the listener is notified inside the synchronization. In the second implementation, this is done outside the synchronization.
I feel that the second one is advised, as it makes less room for potential deadlocks. But I am having trouble to convince myself.
A downside of the second imlementation is that the client might receive 'incorrect' notifications, which happens if it accessed the module prior to the l.notify() statement.
thanks a lot
