How to send and receive messages in Elixir processes

Processes

Processes are the Elixir equivalent of threads. Threads are used in Concurrent Programming to simultaneously carry out functions.

Inter-process messaging

Messages can be transmitted among different processes in Elixir. This operation is done using the send function and the receive do operator.

processId = self()
spawn fn -> send(processId, {:hello, "Message sent and received"}) end
receive do
  {:hello, msg} -> IO.puts msg
end

In this program, a process is started using the spawn function. This process sends a message with the key :hello to the main thread. The main thread’s process ID is obtained using the self() function and stored in the processId variable.

Processes can also be programmed to wait a certain amount of time for a message, and then do something else if no message that matches the possible keys arrives.

processId = self()
spawn fn -> send(processId, {:nonmatchingkey, "Message"}) end
receive do
  {:hello, msg} -> IO.puts msg
  {:world, _msg} -> IO.puts "Key matches"
after
  1_000 -> IO.puts "No matching key received within 1 second"
end

This example does the same things as the previous example, except there is a timer on the receiving operator. When the timer runs out, it outputs the “no” message with any matching key that has been received. The spawned process does send a message; however, this message’s key does not match with any of the set keys.

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