ConcurrentModificationException accessing discovered results

[farble1670]

java.util.ConcurrentModificationException
	at java.util.HashMap$HashIterator.nextNode(HashMap.java:1441)
	at java.util.HashMap$KeyIterator.next(HashMap.java:1465)
	at java.util.Collections$UnmodifiableCollection$1.next(Collections.java:1089)
	at com.clover.nsd_stress.ZeroconfStressActivity.discover$lambda-5(ZeroconfStressActivity.kt:159)

I see the backing services field is a synchronized set, but according to the docs:

It is imperative that the user manually synchronize on the returned set when iterating over it.

However when the field is returned, it's wrapped in a Collections.unmodifiableCollection which just restricts write but not read operations on the wrapped collection. The caller has no idea they need to synchronize because they have no idea the result is a wrapped SynchronizedSet.

One option would be to have the getService() method synchronize on the source collection, making a copy, then return the copy. Or you could back it with a java.util.concurrent collection implementation.

[farble1670]

Here's a good SO post that talks about this.
https://stackoverflow.com/questions/23450227/is-iteration-via-collections-synchronizedset-foreach-guaranteed-to-be-thr/

I happen to be using Kotlin, like this:

discoveredServices.services.forEach { ...

which is not using Set.forEach but it rather some syntactic sugar over the iterator.

[devgianlu]

Are you able to make a PR? I can merge it right now, but can't do it myself.

[farble1670]

Sure, let me stress test it a bit. Thanks for your quick response.

[saket]

Is this related to #17?