key
long key
The 64-bit key of the node. This field should not be changed after the node is inserted
into the data structure. It is not final to allow pooling nodes, and specifying the key
after they are allocated on the heap. It is not volatile, because it must be set before
the insertion into the concurrent data structure -- the concurrent data structure thus
establishes a happens-before relationship between the write to this field and the other
threads that read this field.