Unsafe use of iterator from concurrent collection in Observable through forEach

[thoutbeckers]

This usage is hidden because old package level methods are used dating back to kotlin native's old memory model, but a concurrent list of the observers is iterated through which is unsafe, as any modification while iterating will cause a crash. forEach usage should always be wrapped in synchronized.

This does raise the question if ConcurrentList should even conform to the List interface, it would be better to expose the List only from inside synchronized (as it already does).

val l = ConcurrentMutableList()
// current l is a `List` so you can do this:
l.forEach { /* crashes when the list is changed from the outside*/ } 
l.synchronized {
     forEach { } // already possible and safe.
}

Maybe a ConcurrentList interface should be considered that does not allow mutation, which can be created with a toConcurrentList()/asConcurrentList on a ConcurrentMutableList

[thoutbeckers]

synchronized usage still leaves open same thread modification (using re-entrant locks), instead copy-before-iterate should be used.