Concurrency: Erlang vs Java

Its fashionable to extol the high-performance of Erlang concurrency these days. Programming Erlang, Section 8.11, has this problem:

Write a ring benchmark. Create N processes in a ring. Send a message
round the ring M times so that a total of N * M messages get
sent. Time how long this takes for different values of N and M.

Well, I copied off the Java program from here: http://www.sics.se/~joe/ericsson/du98024.html

And then I wrote this Erlang program:

-module(threadperftest).
-compile(export_all).

timeit() ->
register(mainproc, self()),
io:format(" Procs, Mesgs, SpawnTotal, SpawnProc, RunTotal, RunMesg~n", []),
timeit_aux(1000, 1000, 10000),
init:stop().

timeit_aux(NProcs, NMsgs, NProcsMax) ->
if NProcs =
main([NProcs, NMsgs]),
timeit_aux(NProcs+1000, NMsgs, NProcsMax);
true -> void
end.

main([N, M]) ->
{_, _W0} = statistics(wall_clock),
FirstPid = spawn(fun loop0/0),
% io:format("First: ~p~n", [FirstPid]),
LastPid = setup(N-1, FirstPid),
FirstPid ! LastPid,
{_, W1} = statistics(wall_clock),
LastPid ! M,
receive
stop ->
void
end,
{_, W2} = statistics(wall_clock),
io:format("~6B, ~6B, ~10g, ~10g, ~10g, ~10g~n", [N, M, W1*1.0, 1.0*W1/N, W2*1.0, W2*1000.0/(M*N+N)]).

setup(0, PrevPid) ->
PrevPid;
setup(HowMany, PrevPid) ->
Pid = spawn(fun() -> loop(PrevPid) end),
% io:format("~p: Linking to: ~p~n", [Pid, PrevPid]),
setup(HowMany - 1, Pid).

loop0() ->
receive
LinkedPid when is_pid(LinkedPid) ->
% io:format("First: ~p: Linking to ~p~n", [self(), LinkedPid]),
loop1(LinkedPid);
X ->
erlang:error({unknownMessageError, X, self()})
end.

loop1(LinkedPid) ->
receive
M when is_integer(M), M > 0 ->
% io:format("~p: Received: ~p~n", [self(), M]),
LinkedPid ! (M-1),
loop1(LinkedPid);
M when is_integer(M), M =:= 0 ->
% io:format("~p: Received: ~p, Terminating~n", [self(), M]),
mainproc ! stop,
done;
X ->
erlang:error({unknownMessageError, X, self()})
end.

loop(LinkedPid) ->
receive
M when is_integer(M), M > 0 ->
% io:format("~p: Received: ~p~n", [self(), M]),
LinkedPid ! M,
loop(LinkedPid);
M when is_integer(M), M =:= 0 ->
% io:format("~p: Received: ~p, Terminating~n", [self(), M]),
LinkedPid ! M,
done;
X ->
erlang:error({unknownMessageError, X, self()})
end.

The performance is something like this (all times are in milliseconds, except the last one, which is in microseconds):

 Procs,  Mesgs, SpawnTotal,  SpawnProc,   RunTotal,    RunMesg
1000, 1000, 0.00000e+0, 0.00000e+0, 266.000, 0.265734
2000, 1000, 16.0000, 8.00000e-3, 562.000, 0.280719
3000, 1000, 0.00000e+0, 0.00000e+0, 969.000, 0.322677
4000, 1000, 0.00000e+0, 0.00000e+0, 1672.00, 0.417582
5000, 1000, 15.0000, 3.00000e-3, 2469.00, 0.493307
6000, 1000, 16.0000, 2.66667e-3, 3234.00, 0.538462
7000, 1000, 16.0000, 2.28571e-3, 4015.00, 0.572998
8000, 1000, 16.0000, 2.00000e-3, 4750.00, 0.593157
9000, 1000, 31.0000, 3.44444e-3, 5469.00, 0.607060
10000, 1000, 31.0000, 3.10000e-3, 6375.00, 0.636863

The numbers in the RunMesg column are the time it takes to send one message from one process to another. Why is it increasing? Does the runtime have to do more work to find the target process?

Here is the Java output (program below):

 Procs,  Mesgs, SpawnTotal, SpawnProcs,   RunTotal,   RunMesg
100, 1000, 16.000, 0.160, 15531.000, 15.531
200, 1000, 62.000, 0.310, 27047.000, 27.047
300, 1000, 94.000, 0.313, 37828.000, 37.828
400, 1000, 125.000, 0.313, 46859.000, 46.859
500, 1000, 141.000, 0.282, 54578.000, 54.578
600, 1000, 203.000, 0.338, 60594.000, 60.594
700, 1000, 234.000, 0.334, 65282.000, 65.282
800, 1000, 406.000, 0.508, 68156.000, 68.156
900, 1000, 484.000, 0.538, 69782.000, 69.782
1000, 1000, 735.000, 0.735, 70015.000, 70.015

The last column is in milliseconds whereas for Erlang it was in microseconds, AND the number of procs is 100-1000, whereas for Erlang they were 1000-10,000.

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