Why Netty uses reflection to replace members in sun.nio.ch.SelectorImpl class with array based set?

Question

While browsing through the Netty code base I came across below code block in NioEventLoop.java.

SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet();
Class<?> selectorImplClass =
                Class.forName("sun.nio.ch.SelectorImpl", false, PlatformDependent.getSystemClassLoader());

        // Ensure the current selector implementation is what we can instrument.
        if (!selectorImplClass.isAssignableFrom(selector.getClass())) {
            return selector;
        }

        Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
        Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");

        selectedKeysField.setAccessible(true);
        publicSelectedKeysField.setAccessible(true);

        selectedKeysField.set(selector, selectedKeySet);
        publicSelectedKeysField.set(selector, selectedKeySet);

        selectedKeys = selectedKeySet;

Why Netty uses reflection to change a member of java library class sun.nio.ch.SelectorImpl?

I see one advantage instead of using Set from java collections it uses array based Set, which I believe will be faster. Is there any other specific reason for that ?

Answer 1

It was mainly done to reduce GC. Trustin did some testing here and found this more efficient.