object, but before it increments the object's reference count, all other references to this object are deleted concurrently by other threads and the object is reclaimed, causing the said thread to increment a reference count of a reclaimed object.

In addition to these, if the memory is allocated from a free list, reference counting suffers from poor locality. Reference counting alone cannot move objects to improve cache performance, so high performance collectors implement a tracing garbage collector as well. Most implementations (such