ConcurrentModificationException in ParseTraverser

[shlusiak]

There is still the occasional ConcurrentModificationException in ParseTraverser.

Parse version: 1.25.0

Stack trace:

Fatal Exception: 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:1084)
       at com.parse.ParseTraverser.traverseInternal(ParseTraverser.java:101)
       at com.parse.ParseTraverser.traverseInternal(ParseTraverser.java:95)
       at com.parse.ParseTraverser.traverseInternal(ParseTraverser.java:102)
       at com.parse.ParseTraverser.traverse(ParseTraverser.java:140)
       at com.parse.OfflineStore.saveLocallyAsync(OfflineStore.java:666)
       at com.parse.OfflineStore.access$1300(OfflineStore.java:36)

The issue appears that while ParseObject.keySet() returns a Collections.unmodifiableSet(), the set is a read-through to the underlying HashMap, which is not synchronised.

Parse-SDK-Android/parse/src/main/java/com/parse/ParseObject.java

Lines 1489 to 1497 in 797786f

	/**
	* Returns a set view of the keys contained in this object. This does not include createdAt,
	* updatedAt, authData, or objectId. It does include things like username and ACL.
	*/
	public Set<String> keySet() {
	synchronized (mutex) {
	return Collections.unmodifiableSet(estimatedData.keySet());
	}
	}

I believe we either need to make the estimatedData a synchronised Map, or we need to work on a copy of the set when traversing, to guard against concurrent modifications. Thoughts about making estimatedData a synchronized map?

Parse-SDK-Android/parse/src/main/java/com/parse/ParseTraverser.java

Lines 98 to 103 in 797786f

	} else if (root instanceof ParseObject) {
	if (traverseParseObjects) {
	ParseObject object = (ParseObject) root;
	for (String key : object.keySet()) {
	traverseInternal(object.get(key), true, seen);
	}

[mtrezza]

Closing via #1062