October 22, 2006, at 10:03 AM by-
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SharedData is a concrete subclass of NSMutableData that is used by SharedMemoryByteSlice. It is meant to be shared among multiple SharedMemoryByteSlice. However, it tracks the number of byte slices that references it as its "userCount," and if the userCount is 0, that byte slice is allowed to take the "fast path," and modify the shared data directly instead of making copies.