Enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.
SyncRoot returns an object that can be used to synchronize access to the ICollection. Synchronization is effective only if all threads lock this object before accessing the collection.
Retrieving the value of this property is an O(1) operation.