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9.4. About Deep Copy Subject Mode
If deep copy subject mode is disabled (the default), copying a security data structure makes a reference to the original, rather than copying the entire data structure. This behavior is more efficient, but is prone to data corruption if multiple threads with the same identity clear the subject by means of a flush or logout operation.
Deep copy subject mode causes a complete copy of the data structure and all its associated data to be made, as long as they are marked cloneable. This is more thread-safe, but less efficient.
Deep copy subject mode is configured as part of the security subsystem.