Which java code(file) generates the heartbeat from the datanode and which code(file) listen that heartbeat on the namenode?

[Mohammad Mustaqeem]

Which java code(file) generates the heartbeat from the datanode and
which code(file) listen that heartbeat on the namenode?
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*With regards ---*
*Mohammad Mustaqeem*,
M.Tech (CSE)
MNNIT Allahabad
9026604270