[erlang-questions] Game of Erlang life [was: Load testing in parallel]

Ahmed Ali <>
Tue Aug 14 14:33:25 CEST 2007


Hi Serge,

Actually, I'm not sure if the last 3 "circles" are seperate at all. It seems
to me that "number crunching" circle could be in the first part when
learning Erlang. Same for the 4th one. Are you referring to implementation
of the last 2 circles when you divide it to different stages?

Best regards,

Ahmed Al-Issaei

On 8/14/07, Serge Aleynikov <> wrote:
>
> So far the best resource of OTP documentation is the on-line reference:
> http://www.erlang.org/doc.
>
> Sometimes this documentation may seem odd or vague for newcomers, yet
> the more you learn Erlang/OTP the more you understand and appreciate the
> format, depth and value of the content.
>
> Once you mastered first "Programming Erlang" chapters (ch.1-15,
> excluding OTP ones) I suggest that you start by studying on-line module
> documentation under "Basic Applications": stdlib and kernel.  They
> expose a wealth of functions, many of which you'll find used in all
> projects.  Despite the fact that it may seem like a lot of information,
> if you approach this studying methodically and patiently, you'll be able
> to filter content on the module level first (i.e. gaining high-level
> understanding of what each module does) and then in those modules that
> seem to trigger more of your interest (like kernel/erlang, stdlib/io,
> stdlib/ets, etc.) study documented functions.
>
> Don't worry about OTP (aside from stdlib and kernel applications) as
> much in the beginning - when you feel you have a good grasp on basic
> functions available in the two apps above, read the Design Principles
> guide [1] to understand OTP behaviors - which is the "meat" part of the
> framework that gives you the power of increasing your coding
> productivity by implying practical and reliable abstractions.
>
> At this point, go back to "Programming Erlang" and study the OTP-related
> chapters (ch.16 onward) that give you application examples of how to use
>   behaviors.  This will conclude your "first circle of Erlang life" and
> give you enough knowledge to move on to exploiting the power of
> Erlang/OTP in your projects.
>
> The "second circle of Erlang life" will begin when your curiosity will
> drive you to understanding that Erlang is *open source* and you'll start
> exploring the sources of OTP applications included in distribution.
> That is when you'll actually begin seeing that on-line documentation is
> rather good.  When you are comfortable with OTP code you may find bugs
> and post them to the  list, and also make some
> contributions.
>
> The "third circle of Erlang life" will begin when you discover that
> Erlang's performance sucks at number-crunching applications (which are
> not the domain of problems Erlang was designed for), and begin writing
> ports and drivers to overcome these bottlenecks.  Additionally As a
> conclusion of this circle you'll be quite fascinated at how much thought
> was put in preventing mis-behaving user code crash the Erlang emulator.
>
> The "forth circle of Erlang life" will begin when your curiosity drives
> you to studying sources of the Erlang emulator.  Here you'll learn how
> I/O multiplexing, garbage collection, bytecode execution, etc. is done,
> and answer some of more advanced questions you might have accumulated
> about features of the run-time system.
>
> By this time others will find that you are "... more object oriented in
> thinking than most of his C++ guys" [2]. The "next circle of Erlang
> life" will begin when you manage to get a job that will let your
> evolution as an Erlang programmer use acquired knowledge during
> day-time.  Since not many companies know the hidden powers of Erlang,
> this will largely depend on your abilities to show the strength of
> Erlang/OTP development to your manager, find suitable projects, and
> generate spin to share this knowledge and apply it in your organization.
>
> Regards,
>
> Serge
>
>
> [1] http://www.erlang.org/doc/design_principles/part_frame.html
> [2]
> http://www.erlang.org/pipermail/erlang-questions/2007-August/028392.html
>
>
> David Mitchell wrote:
> > Great tip Serge!
> >
> > Like many others, I'm new to Erlang - I've read through the
> > "Programming Erlang" book, "Thinking in Erlang" and various PDFs at
> > the main Erlang site.  I've written a few trivial bits of code,
> > identified and sorted out a bunch of problems I've created, and now
> > I'm moving into using Erlang for larger projects.  However, I've never
> > come across info about now() and timer.diff() before; like Ahmed, I've
> > been using statistics(wall_clock) for profiling purposes.
> >
> > Where is that type of info documented?  Is it only in the various
> > library APIs (and thus I'll have to work through each of these to get
> > a handle on this type of info), or is there some "best practices"-type
> > documentation I haven't yet stumbled on?  I don't mind putting in the
> > time to do my research, but I suspect I'm not yet across all the
> > "good" sources of info.
> >
> > Thanks in advance
> >
> > Dave M.
> >
> > On 13/08/07, Serge Aleynikov <> wrote:
> >> You have several problems with this code:
> >>
> >> 1. Since you don't provide implementation of generate_lists/3, I assume
> >>     it returns a flat list.  In this case in the start function you
> call:
> >>
> >>        spawn(?MODULE, run_process,  [Num, Op, Head, Pid]),
> >>
> >>     if here Head is not a list, whereas run_process/4 expects a list
> >>     as the third argument, lists:map/2 function would
> >>     crashes the process silently.  You can fix it by changing that line
> >>     to:
> >>        spawn(?MODULE, run_process,  [Num, Op, [Head], Pid]),
> >>
> >>
> >> 2. Also you use the following call to obtain time:
> >>
> >>     {_, Wallclock_Time_Since_Last_Call} = statistics(wall_clock).
> >>
> >>     Wallclock_Time_Since_Last_Call is time in milliseconds, so unless
> >>     evaluated function takes more than a millisecond you'd get a 0.
> >>
> >>     Moreover, unfortunately Wallclock_Time_Since_Last_Call is a
> *globally
> >>     shared* counter, so any process that calls statistics would cause a
> >>     reset of this value.  So in a concurrent system where many
> processes
> >>     use this function you'll likely always get a zero.
> >>
> >>     use T1 = now(), ..., T2 = now(), ... timer:now_diff(T2, T1)
> >>     to measure time.
> >>
> >> Serge
> >>
> >>
> >>
> >> Ahmed Ali wrote:
> >>> Hi all,
> >>>
> >>> I've been trying to load test a function in my code. The way I'm doing
> it is
> >>> to generate lists of the data I want to process, start a process for
> each
> >>> list and calculate runtime for each process. The function that I
> implemented
> >>> will call a  WebService operation in a different host for each data.
> >>>
> >>> I have the code below for this test. what I do is basically run
> >>> load_test(10, 1000) to generate 10 lists, each with 1000 data in it.
> >>>
> >>> The problem is that WebService call is done successfully but I don't
> get any
> >>> output for the statistics. When I run the code sequentially (i.e.
> instead of
> >>> spawn the call to run_process, I call run_process directly) I get the
> output
> >>> with no issues. Is there something that I missed in the code below? I
> >>> appreciate your help.
> >>>
> >>> Best regards,
> >>>
> >>> Ahmed Al-Issaei
> >>>
> >>> run_process(Num, Fun, List, _Pid) ->
> >>>     statistics(wall_clock),
> >>>     io:format("load testing process~n"),
> >>>     lists:map(Fun, List),
> >>>     {_, Time2} = statistics(wall_clock),
> >>>     U2 = Time2 / 1000,
> >>>     io:format("Num (~s) done: total time = ~p~n",[Num, U2]).
> >>>
> >>> start(_N, _Op, [], _Pid) ->
> >>>     true;
> >>> start(Num, Op, Final, Pid) ->
> >>>     [Head | Rest] = Final,
> >>>     spawn(?MODULE, run_process,  [Num, Op, Head, Pid]),
> >>>     start(Num-1, Op, Rest, Pid).
> >>>
> >>> load_test(Threads, Size) ->
> >>>     List = generate_lists(Threads, Size, []),
> >>>     Op = fun(X) -> call_ws_create(X) end,
> >>>     start(Threads, Op, List, self()).
>
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