Distributed runtime concepts and data exchange between task

Data exchange in Flink is built around the following design principles:

(1) The control flow for data exchange (i.e., the message passing in order to initiate the exchange) is receiver-initiated, much like the original MapReduce.

(2) The data flow for data exchange, i.e., the actual transfer of data over the wire is abstracted by the notion of an IntermediateResult, and is pluggable. This means that the system can support both streaming data transfer and batch data transfer with the same implementation.