Erlang Programming/Processes

Erlang Processes and Messages Processes are easy to create and control in Erlang. The program chain_hello.erl builds a chain of processes as long as you like. Each process creates one process then sends a message to it. The program creates a chain of N processes which each print out "hello world!<N>" (where <N> is some integer). Processes send messages to and receive messages from one another. Messages are read with pattern matching. The messages are matched in a fifo (first in, first out) way. Note 1: The order of the final output depends on process scheduling. Note 2: Time flows downward (in each vertical line, see note 1). This is a Process Message Diagram for the execution of: chain_hello:start(1). start(1) | spawns -----------> listen(1) | | | spawns --------------------> listen(0) | | | | sends ----> speak ----------> prints --> "hello world 0" | | | sends --> speak --> prints --> "hello world 1" | | | ok ok Program listing for: chain_hello.erl -module(chain_hello). -compile(export_all). % start(N)-> % startup Pid1 = spawn(chain_hello, listen, [N]), Pid1 ! speak, io:format("done \n"). % listen(0)-> % base case receive speak -> io:format("hello world!~w\n", [0]) end; listen(N)-> % recursive case Pid2 = spawn(chain_hello, listen, [N-1]), Pid2 ! speak, receive speak -> io:format("hello world!~w\n", [N]) end. % ---- sample output ---- % % % 14> chain_hello:start(4). % done % hello world!4 % hello world!3 % hello world!2 % okhello world!1 % hello world!0