Concurrent Programming II

1.Concurrency is easy…? <br /><br />( <a href="http://armstrongonsoftware.blogspot.com/2006/08/concurrency-is-easy.html">http://armstrongonsoftware.blogspot.com/2006/08/concurrency-is-easy.html</a> )<br /><br /><br />2.Sequential Programming<br /><br />-module(factorial).<br />-export([factoriala/1, factorialb/1, factorialc/1, factoriald/1]).<br /><br /><br />%Simplest:<br />factoriala(0) -> 1;<br />factoriala(N) -> N * factoriala(N - 1).<br /><br /><br />%Using function guards:<br />factorialb(0) -> 1;<br />factorialb(N) when N > 0 -> N * factorialb(N - 1).<br /><br /><br />%Using if:<br />factorialc(N) -><br /> if<br /> N == 0 -> 1;<br /> N > 0 -> N * factorialc(N - 1)<br />end.<br /><br /><br />%Using case:<br />factoriald(N) -><br /> case N of<br /> 0 -> 1;<br /> N when N > 0 -> N * factoriald(N - 1)<br />end.<br /><br /><br /><br />-module(set).<br />-export([new/0, add_element/2, del_element/2,is_element/2, is_empty/1, union/2, intersection/2]).<br /><br />new() -> [].<br /><br />is_element(H, [H|_]) -> true;<br />is_element(H, [_|Set]) -> is_element(H, Set);<br />is_element(_, []) -> false.<br /><br /><br />is_empty([]) -> true;<br />is_empty(_) -> false<br /><br />add_element(X, Set) -><br />case is_element(X, Set) of<br /> true -> Set;<br /> false -> [X|Set]<br />end.<br /><br /><br />del_element(X, [X|T]) -> T;<br />del_element(X, [Y|T]) -> [Y|del_element(X,T)];<br />del_element(_, []) -> [].<br /><br /><br />union([H|T], Set) -> union(T, add_element(H, Set));<br />union([], Set) -> Set.<br /><br /><br />intersection(S1, S2) -> intersection(S1, S2, []).<br />intersection([], _, S) -> S;<br />intersection([H|T], S1, S) -><br />case is_element(H,S1) of<br /> true -> intersection(T, S1, [H|S]);<br /> false -> intersection(T, S1, S)<br />end.<br /><br /><br />3.concurrent programming<br /><br />Processes and communication between processes are fundamental concepts in Erlang.<br /><br />1. Process Create<br /><br /> Pid = spawn(Module, FunctionName, ArgumentList)<br /><br /> 2. Inter-process Communication<br /><br /> Pid ! Message<br /><br /> receive<br /> Message1 [when Guard1] ->Actions1 ;<br /> Message2 [when Guard2] ->Actions2 ;<br /> _AnyMessage -> Actions3 ;<br /> after Timeout ->Action4 <br /> ...<br /> end.<br /> <br /> 3.Receiving messages from a specific process<br /> <br /> Pid ! {self(),abc}<br /><br /> receive<br /> {Pid,Msg} -><br /> ...<br /> end<br /> <br /><br />4. Examples<br /><br /> a)<br /> -module(cfac).<br /> -export([start/0,loop/0]).<br /> -import(factorial,[factoriala/1]).<br /><br /> start() ->spawn(counter, loop, []).<br /> <br /> loop() -><br /> receive<br /> {fac,Val}-> io:format("(from:~p)fac ~p=~p ~n",[node(),Val, <br /> factoriala(Val)]),loop();<br /> {exit}->io:format("end~n",[]);<br /> _->loop()<br /> end.<br /><br /><br /> b) performance testing<br /><br /> <br /> c) programming with socket <br /> -module(geturl).<br /> -export([start/2,senddata/1,dataarrive/1,startN/3]).<br /> -define(TCP_OPTIONS,[list, {packet, 0}, {active, false}, {reuseaddr, <br /> true}]).<br /><br /> start(Url,Port)-><br /> case gen_tcp:connect(Url,Port ,?TCP_OPTIONS ) of<br /> {ok,CSocket}->geturl:senddata(CSocket);<br /> {error,Why}->Why<br /> end.<br /> <br /> senddata(Socket)-><br /> Data="GET / HTTP/1.0\r\nConnection: close\r\nCache-Control: <br /> no-cache\r\n\r\n",<br /> io:format("~p~n",[Socket]),<br /> <br /> case gen_tcp:send(Socket,Data) of<br /> ok->io:format("send:~p~n",[Data]),dataarrive(Socket);<br /> {error, Why}->io:format("send_socket close:~p~n",[Why])<br /> end. <br /><br /> dataarrive(Socket)-> <br /> case gen_tcp:recv(Socket, 0) of<br /> { ok, Data} ->io:format("receive:~p~n",[Data]),<br /> dataarrive(Socket);<br /> {error, Why} ->io:format("dataarrive_socket <br /> close:~p~n",[Why])<br /> end.<br /><br /> startN(_,_,0)->io:format("~p~n",["end"]);<br /> startN(Url,Port,Num)->spawn(geturl,start,[Url,Port]), <br /> startN(Url,Port,Num-1).<br /><br /><br /> d) Distributes Programming<br /><br /> erl –sname local<br /> erl –sname remote<br /><br /> Pid=rpc:call(remote@se6,cfac,start,[]).<br /> Pid ! {fac,10}.<br /> <br /><br /><br />5.References<br /><br />[1] J. Armstrong, R. Virding, C. Wikstr¨om, and M. Williams. Concurrent Programming in Erlang.<br />[2] J. Armstrong.Erlang Programming.