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Erlang / Erlang Advanced Interview questions

What is the difference between rpc:call and simply sending a message to a remote PID?

Sending Pid ! Msg to a remote PID is a raw, asynchronous, fire-and-forget send — you get no return value unless the receiving process is written to reply, and you must already know that specific PID. rpc:call/4 is a higher-level convenience built on top of message passing that packages up "run this function on that node and hand me back the result" as a single blocking call, without needing a running process on the other end designed to answer you.

Raw message sendrpc:call/4
Requires a target PID that already knows how to reply. Targets an arbitrary Module:Function on any connected node.
Asynchronous; caller must implement its own receive/reply protocol. Synchronous; blocks and returns the function's result directly.

In practice, rpc:call is reached for ad hoc cross-node operations (admin tasks, debugging, one-off queries), while application code that needs an ongoing conversation with a remote process typically talks to a specific gen_server via its PID or a registered name instead.

What must you already have to send a raw message to a remote process?
What does rpc:call/4 provide that a raw message send does not?

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