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Complete exercise 23.3
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‎chapter_23/exercise_3/.gitignore‎

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_build

‎chapter_23/exercise_3/rebar.config‎

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{deps, []}.

‎chapter_23/exercise_3/rebar.lock‎

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[].

‎chapter_23/exercise_3/src/lib_lin.erl‎

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%% ---
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%% Excerpted from "Programming Erlang, Second Edition",
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%% published by The Pragmatic Bookshelf.
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%% Copyrights apply to this code. It may not be used to create training material,
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%% courses, books, articles, and the like. Contact us if you are in doubt.
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%% We make no guarantees that this code is fit for any purpose.
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%% Visit http://www.pragmaticprogrammer.com/titles/jaerlang2 for more book information.
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%%---
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-module(lib_lin).
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%% (c) Joe Armstrong 1998
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-export([pow/3, inv/2, solve/2, str2int/1, int2str/1, gcd/2]).
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%% pow(A, B, M) => (A^B) mod M
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%% examples pow(9726,3533,11413) = 5761
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%% pow(5971,6597,11413) = 9726
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pow(A, 1, M) ->
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AremM;
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pow(A, 2, M) ->
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A*AremM;
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pow(A, B, M) ->
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B1=Bdiv2,
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B2=B-B1,
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%% B2 = B1 or B1+1
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P=pow(A, B1, M),
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caseB2of
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B1 -> (P*P) remM;
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_ -> (P*P*A) remM
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end.
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%% inv(A, B) = C | no_inverse
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%% computes C such that
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%% A*C mod B = 1
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%% computes A^-1 mod B
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%% examples inv(28, 75) = 67.
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%% inv(3533, 11200) = 6597
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%% inv(6597, 11200) = 3533
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inv(A, B) ->
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casesolve(A, B) of
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{X, _} ->
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ifX<0 -> X+B;
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true -> X
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end;
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_ ->
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no_inverse
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end.
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%% solve(A, B) =>{X, Y} | insoluble
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%% solve the linear congruence
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%% A * X - B * Y = 1
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solve(A, B) ->
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casecatchs(A,B) of
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insoluble -> insoluble;
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{X, Y} ->
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caseA*X-B*Yof
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1 ->{X, Y};
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_Other -> error
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end
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end.
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s(_, 0) ->throw(insoluble);
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s(_, 1) ->{0, -1};
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s(_, -1) ->{0, 1};
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s(A, B) ->
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K1=AdivB,
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K2=A-K1*B,
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{Tmp, X} =s(B, -K2),
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{X, K1*X-Tmp}.
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%% converts a string to a base 256 integer
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%% converts a base 256 integer to a string
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str2int(Str) ->str2int(Str, 0).
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str2int([H|T], N) ->str2int(T, N*256+H);
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str2int([], N) ->N.
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int2str(N) ->int2str(N, []).
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int2str(N, L) whenN=<0->L;
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int2str(N, L) ->
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N1=Ndiv256,
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H=N-N1*256,
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int2str(N1, [H|L]).
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%% greatest common devisor
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gcd(A, B) whenA<B->gcd(B, A);
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gcd(A, 0) ->A;
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gcd(A, B) ->gcd(B, AremB).

‎chapter_23/exercise_3/src/lib_primes.erl‎

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%% ---
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%% Excerpted from "Programming Erlang, Second Edition",
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%% published by The Pragmatic Bookshelf.
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%% Copyrights apply to this code. It may not be used to create training material,
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%% courses, books, articles, and the like. Contact us if you are in doubt.
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%% We make no guarantees that this code is fit for any purpose.
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%% Visit http://www.pragmaticprogrammer.com/titles/jaerlang2 for more book information.
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%%---
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-module(lib_primes).
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-export([make_prime/1, is_prime/1, make_random_int/1]).
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make_prime(1) ->%% <label id="make_primes1" />
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lists:nth(random:uniform(4), [2,3,5,7]);
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make_prime(K) whenK>0->%% <label id="make_primes2" />
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new_seed(),
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N=make_random_int(K),
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ifN>3 ->
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io:format("Generating a ~w digit prime ",[K]),
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MaxTries=N-3,
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P1=make_prime(MaxTries, N+1),
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io:format("~n",[]),
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P1;
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true ->
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make_prime(K)
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end. %% <label id="make_primes3" />
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make_prime(0, _) ->%% <label id="prime_loop1" />
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exit(impossible);
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make_prime(K, P) ->
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io:format(".",[]),
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caseis_prime(P) of
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true -> P;
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false -> make_prime(K-1, P+1)
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end. %% <label id="prime_loop2" />
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is_prime(D) whenD<10->
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lists:member(D, [2,3,5,7]);
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is_prime(D) ->
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new_seed(),
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is_prime(D, 100).
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is_prime(D, Ntests) ->
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N=length(integer_to_list(D)) -1,
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is_prime(Ntests, D, N).
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is_prime(0, _, _) ->true; %% <label id="is_prime_1" />
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is_prime(Ntest, N, Len) ->%% <label id="is_prime_2" />
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K=random:uniform(Len),
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%% A is a random number less than K
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A=make_random_int(K),
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if
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A<N ->
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caselib_lin:pow(A,N,N) of
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A -> is_prime(Ntest-1,N,Len);
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_ -> false
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end;
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true ->
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is_prime(Ntest, N, Len)
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end. %% <label id="is_prime_3" />
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%% make_random_int(N) -> a random integer with N digits.
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make_random_int(N) ->new_seed(), make_random_int(N, 0). %% <label id="make_ran_int1" />
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make_random_int(0, D) ->D;
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make_random_int(N, D) ->
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make_random_int(N-1, D*10+ (random:uniform(10)-1)). %% <label id="make_ran_int2" />
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%END:make_ran_int
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new_seed() ->
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{_,_,X} =erlang:now(),
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{H,M,S} =time(),
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H1=H*Xrem32767,
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M1=M*Xrem32767,
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S1=S*Xrem32767,
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put(random_seed,{H1,M1,S1}).
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‎chapter_23/exercise_3/src/prime_tester_load_balancer.erl‎

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%%%-------------------------------------------------------------------
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%%% @author trevor
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%%% @copyright (C) 2020, trevor
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%%% @doc
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%%% The queue server to handle queuing sending individual
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%%% @end
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%%%-------------------------------------------------------------------
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-module(prime_tester_load_balancer).
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-behaviour(gen_server).
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%% API
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-export([start_link/1, is_prime/1]).
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%% gen_server callbacks
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-export([init/1,
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handle_call/3,
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handle_cast/2,
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handle_info/2,
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terminate/2,
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code_change/3]).
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-define(SERVER, ?MODULE).
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-record(state,{limit=0,
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free_pids=[],
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jobs=#{},
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queue=queue:new()}).
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%%%===================================================================
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%%% API
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%%%===================================================================
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%%--------------------------------------------------------------------
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%% @doc
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%% Starts the server
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%%
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%% @end
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%%--------------------------------------------------------------------
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-specstart_link(Limit::integer()) ->{ok, Pid::pid()} | ignore |{error, Error::any()}.
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start_link(Limit) whenis_integer(Limit) ->
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gen_server:start_link({local, ?SERVER}, ?MODULE,{Limit}, []).
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-specis_prime(Number::integer()) ->any().
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is_prime(Number) ->
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gen_server:call(?SERVER,{is_prime, Number}).
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%%%===================================================================
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%%% gen_server callbacks
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%%%===================================================================
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init({Limit}) ->
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% Start up all workers
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Pids=lists:map(fun(_Num) ->
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% Start the worker
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{ok, Pid} =supervisor:start_child(prime_tester_worker_sup, []),
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_Ref=erlang:monitor(process, Pid),
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Pid
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end, lists:seq(1, Limit)),
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% Store pids in state
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{ok, #state{free_pids=Pids}}.
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handle_call({is_prime, Number}, From, State=#state{free_pids=[], queue=Q}) ->
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% If we've already hit our limit for workers queue the request
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{noreply, State#state{queue=queue:in({From, Number}, Q)}};
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handle_call({is_prime, Number}, From, State=#state{free_pids=[Pid|Pids], jobs=R}) ->
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% If we still haven't hit our limit for workers, give the worker the new job
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ok=prime_tester_worker:is_prime(Pid, Number),
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% We will reply when the worker replies to us
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{noreply, State#state{free_pids=Pids, jobs=maps:put(Pid,{From, Number}, R)}};
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handle_call(_Request, _From, State) ->
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Reply=ok,
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{reply, Reply, State}.
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handle_cast({worker_result, Pid, Result}, State=#state{free_pids=FreePids, jobs=Jobs, queue=Queue}) ->
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% Lookup client pid in map
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casemaps:is_key(Pid, Jobs) of
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true ->
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% Send the reply back to the original `From` pid
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{From, _Number} =maps:get(Pid, Jobs),
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gen_server:reply(From,{ok, Result}),
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% Start the next job
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casequeue:out(Queue) of
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{{value,{From, Number}}, NewQueue} ->
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% Put the old pid back in the list of pids and get the new one
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[NewPid|RestPids] =FreePids,
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NewFreePids=RestPids++ [Pid],
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% Start the new job
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ok=prime_tester_worker:is_prime(NewPid, Number),
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NewJobs=maps:put(NewPid,{From, Number}, maps:remove(Pid, Jobs)),
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{noreply, State#state{free_pids=NewFreePids, jobs=NewJobs, queue=NewQueue}};
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{empty, _} ->
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% If empty no change
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{noreply, State#state{free_pids=FreePids++ [Pid], jobs=maps:remove(Pid, Jobs)}}
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end;
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false ->
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% If we don't find a pid in a map ignore this message
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{noreply, State#state{jobs=maps:remove(Pid, Jobs)}}
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end;
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handle_cast(_Msg, State) ->
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{noreply, State}.
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% Handle getting a down message from a finished worker
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handle_info({'DOWN', _Ref, process, Pid, _}, State=#state{jobs=Pids}) ->
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casemaps:is_key(Pid, Pids) of
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true ->
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handle_down_worker(Pid, State);
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false -> %% Not our responsibility
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{noreply, State}
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end;
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handle_info(_Info, State) ->
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{noreply, State}.
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terminate(_Reason, _State) ->
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ok.
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code_change(_OldVsn, State, _Extra) ->
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{ok, State}.
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%%%===================================================================
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%%% Internal functions
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%%%===================================================================
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handle_down_worker(Pid, State=#state{limit=Limit, jobs=Pids, queue=Queue}) ->
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io:format("got worker down"),
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casequeue:out(Queue) of
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{{value,{From, Number}}, NewQueue} ->
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{ok, Pid} =supervisor:start_child(prime_tester_worker_sup, [Number]),
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NewPid=erlang:monitor(process, Pid),
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NewPids=gb_sets:insert(NewPid, maps:remove(Pid,Pids)),
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gen_server:reply(From,{ok, Pid}),
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{noreply, State#state{jobs=NewPids, queue=NewQueue}};
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{empty, _} ->
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% If nothing in the queue continue as before
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{noreply, State#state{limit=Limit+1, jobs=gb_sets:delete(Pid, Pids)}}
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end.

‎chapter_23/exercise_3/src/prime_tester_server_test.erl‎

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-module(prime_tester_server_test).
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-export([run/0]).
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run() ->
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% Start the application
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ok=application:start(sellaprime),
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CallPrimeTester=fun(Number) ->
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io:format("Calling prime server~n"),
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Result=prime_tester_server:is_prime(Number),
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io:format("Got a result from prime server: ~p~n", [Result])
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end,
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% Queue some tasks
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spawn_monitor(fun() ->CallPrimeTester(7) end),
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spawn_monitor(fun() ->CallPrimeTester(8) end),
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spawn_monitor(fun() ->CallPrimeTester(9) end),
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% Stop the application
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%ok = application:stop(sellaprime).
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ok.

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