JoinBlock<T1, T2>.Complete Method
Signals to the IDataflowBlock that it should not accept nor produce any more messages nor consume any more postponed messages.
Assembly: System.Threading.Tasks.Dataflow (in System.Threading.Tasks.Dataflow.dll)
After has been called on a dataflow block, that block will complete, and its Completion task will enter a final state after it has processed all previously available data. will not block waiting for completion to occur, but rather will initiate the request; to wait for completion to occur, the Completion task may be used.