The static method, javafx.collections.FXCollections.synchronizedObservableList(ObservableList<E>) provides functionality similar to java.util.Collections.synchronizedList(List<T>). However, if you look at the documentation for synchronizedList() it describes the importance of passing the resulting list into a synchronized block before you iterate through it. Unfortunately, this does not work for a list obtained through synchronizedObservableList(). Instead, attempting to iterate through a SynchronizedObservableList will most likely result in a ConcurrentModificationException being thrown.

I have experience this on 8u20. Looking at the code, I would expect similar results in 8u40 or 9.

I believe this can be easily improved by adding a new constructor for the SynchronizedList static, nested class in FXCollections. This constructor would have the signature: SynchronizedList(List<T> list). It would assign "this" to the mutex member variable. The SynchronizedObservableList static, nested class would then use this variant of its superclass constructor.

The code currently appears as follows:

    private static class SynchronizedObservableList<T> {
        SynchronizedObservableList(ObservableList<T> seq) {
            this(seq, new Object());
        }
    }

I believe that we should change this to:

    private static class SynchronizedList<T> {
        SynchronizedList(List<T> list) {
            this.backingList = list;
            this.mutex = this;
        }
    }

    private static class SynchronizedObservableList<T> {
        SynchronizedObservableList(ObservableList<T> seq) {
            super(seq);
            this.backingList = seq;
            ...
            // Code to setup listener member
    }

There are of course other ways of solving this problem. The approach above seems to more closely match what is being done for the SynchronizedCollection and SynchronizedList nested classes in java.util.Collections.