Distributed Erlang - Workshop

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1、HansSvenssonErlangprogramsaremadeof(lotsof)processesProcessescansendmessagestoeachotherMessagesmayormaynotbereceived,tobesure,oneneedsaconfirmationmessagePairsofprocessescanbelinkedtogether,ifoneoftheprocessesdies,theotherprocessisnotifiedofthedeath,andthereasonE

2、rlangprogramsaremadeof(lotsof)processesProcessescansendmessagestoeachotherMessagesmayormaynotbereceived,tobesureoneneedsaconfirmationmessagePairsofprocessescanbelinkedtogether,ifoneoftheprocessesdies,theotherprocessisnotifiedofthedeath,andthereasonPid=spawn(Fun)Createsafreshprocesst

3、hatisgoingtoevaluateFun.Thespawnedprocessisrunninginparallelwiththecurrentprocess.Thereturnedprocessidentifier(Pid)isunique,andcanbeusedtosendmessagestotheprocess.Spawncanalsobecalledwiththreearguments:spawn(Module,Function,Arguments)Pid!MessageSendsamessage(Message)totheprocessidentif

4、iedbyPid.Sendingamessageisasynchronous,i.e.thesenderdoesnotwaitforthemessagetobedelivered.ThesendexpressionreturnsMessage.receive…endReceivingamessageisblocking,i.e.thereceivingprocesswillwaituntilamatchingmessagearrives.receivePattern1[whenGuard1]->Exprs1;Pattern2[whenGuard2]->Exprs2;

5、…endPatternsandguardsaresimilartopatternsandguardsinfunctionclausesMessagesarematchedagainstthepatternsfromtoptobottom.(Thefirstmessageistriedagainsteverypatternbeforeconsideringasecondmessage).Wewilllookatsomecodehandlinggeometricalshapes{square,X}{circle,R}{rectangle,W,H}Wewan

6、ttocomputeareaButthistimeinaseparateprocess!Recallthearea/1function%%Areaofageometricalfigurearea({square,X})->X*X;area({circle,R})->R*R*?PI;area({rectangle,H,W})->H*W.-export([loop/0]).loop()->receiveShape->io:format(“Areaof~pis~p~n”,[Shape,area(Shape)]),loop()end.1>Pid=spawn(funare

7、a_server:loop/0).<0.47.0>2>Pid!{rectangle,4,7}.Areaof{rectangle,4,7}is28{rectangle,4,7}Theresultofasend3>Pid!{circle,5}.operationisthemessage!Areaof{circle,5}is74.5375{circle,5}4>Pid!{triangle,2,4,7}.{triangle,2,4,7}Theloop-process5>Pid!{circle,3}.willcrash!{circle,3}Ok,thatworks,bu