receive ... after in Erlang

after puts a clock on receive.

%% after puts a clock on receive: no message, take the timeout arm.
main(_) ->
    %% Nobody ever calls, so the timeout arm answers.
    receive
        {call, Line} -> io:format("Ring on ~p~n", [Line])
    after 50 ->
        io:format("Quiet board, going to lunch~n")
    end,

    %% A message already waiting wins over the clock.
    self() ! {call, 3},
    receive
        {call, L} -> io:format("Caught line ~p in time~n", [L])
    after 1000 ->
        io:format("Never reached~n")
    end.

How it works

1. No matching message by the deadline: the after arm runs.
2. A waiting message always beats the clock.
3. self() ! Msg queues a message to your own mailbox.

Keywords and builtins used here

• after
• end
• format
• main
• receive

The run, in numbers

Lines

16

Characters to type

429

Tokens

94

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 94 seconds.

Type this snippet

Step 2 of 4 in Processes, step 26 of 31 in Language basics.

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