Processes and Messages

Code

# Spawn a process
pid = spawn(fn ->
  receive do
    {:hello, from} ->
      send(from, {:hi, self()})
      receive do
        msg -> IO.puts("Got: #{inspect(msg)}")
      end
    {:bye} ->
      IO.puts("Goodbye!")
  end
end)

# Send a message
send(pid, {:hello, self()})

# Receive (with timeout)
receive do
  {:hi, pid2} -> IO.puts("Received hi from #{inspect(pid2)}")
after
  1000 -> IO.puts("Timeout")
end

# Process info
Process.alive?(pid)  # true/false
Process.list()        # all PIDs

# Link (dies together)
spawn_link(fn -> exit(:boom) end)
# Traps EXIT if Process.flag(:trap_exit, true)

Explanation

Elixir processes are lightweight (thousands can run concurrently) — they don't share memory, they communicate via messages. send/receive is the core primitive. receive blocks until a matching message arrives (or after timeout). spawn_link creates a linked process — if one dies, the other does too (unless trapping exits). This is the Actor model on the BEAM VM.

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