Github user sachingoel0101 commented on the pull request:
https://github.com/apache/flink/pull/975#issuecomment-127331693
The basic methodology is this:
1. `TaskManager` keeps asking `JobManager` for running `TaskManagers` at
some interval, same as the `heartbeat` interval.
2. `TaskManager` sets up a `MessageHandler` when it first associated itself
with a `JobManager` and provides it with a gateway to itself.
3. `MessageHandler` sets up separate `TaskMessageHandlers` for all tasks
registered on the `TaskManager` and passes the pointers to the
`RuntimeEnvironment -> PackTask -> RuntimeContext`, whereby user can
`broadcast` the messages derived from the interface `TaskMessage`.
4. User can fetch all messages by calling `receive` from `RuntimeContext`
and is provided a list of all messages available for this task. __Messages will
be delivered only once. __
5. There is a separate limited size `queue` associated with each `Task`,
which serves messages to all parallel instances of a `Task` exactly once,
without duplicating them.
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