Posted on 14 December 2012
I got the invitation to talk at the Programming Environments Meetup at the Centrum for Mathematics and Computer Science (CWI).
The talk was part of a weekly lecture series at the Software Engineering department of the CWI. As an introduction, instead of the obvious Erlang - the Movie video, I started with another one called Erlang - the Ghetto:
The presentation itself is an assemblage of different other Erlang presentations I found on the web. It starts with the language fundamentals and its functional aspects; then continuing onto concurrency and its "Let it crash" philosophy. Then headed on to explain OTP, process supervision and the gen_server. Finally I touched upon performance issues, tuning aspects and common pitfalls.
It was refreshing to give a talk to such skilled people :-)
I illustrated the actor / message passing chapter with the code below: A shell script which processes a number of files in parallel, with limited parallelism and a "worker queue".
| #!/usr/bin/escript | |
| %% -*- mode: erlang -*- | |
| main(Files) -> | |
| NumWorkers = 3, | |
| Parent = self(), | |
| Workers = [spawn_link(fun() -> worker(Parent) end) || _ <- lists:seq(1, NumWorkers)], | |
| serve_queue(Files), | |
| %% We need to wait for the workers to finish; with escript, the VM exits when the main process stops | |
| [Worker ! stop || Worker <- Workers], | |
| wait_stop(Workers). | |
| serve_queue([]) -> | |
| ok; | |
| serve_queue([File|Rest]) -> | |
| receive | |
| {want_file, Pid} -> | |
| Pid ! {work, File}, | |
| serve_queue(Rest) | |
| end. | |
| wait_stop([]) -> | |
| ok; | |
| wait_stop([_|R]) -> | |
| receive | |
| ok -> | |
| wait_stop(R) | |
| end. | |
| worker(Parent) -> | |
| Parent ! {want_file, self()}, | |
| receive | |
| {work, File} -> | |
| resize(File), | |
| worker(Parent); | |
| stop -> | |
| Parent ! ok | |
| end. | |
| resize(F) -> | |
| io:format("Resizing: ~p~n", [F]), | |
| %% os:cmd("mogrify -resize 300x300 " ++ F), | |
| ok. |
Don't use this in production though! This is just meant as a simple shell script demonstrating processes and messaging.
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