CODEWITHSUNDEEP
erlang
user2355058
user2355058

Reputation:

Erlang dynamic variable names on each iteration

Program is working now. The simplest solution was the best. The registered processes did not work. I actually was having some trouble with the call to await/2 from the base case of start/6. Turned out I was using the modified list T_T.

%variables
T = 10000000,       
P = 4,              
Tpart = 2500000,            
Width = 1.0 / T,
Pi = pi(T, P, [], 1), calls pi/4 and gets a list of pid

start(T, P, Tpart, Width, Pi, 1). %calls start with the Pi variable which should contain 4 Pids



    % create a list of P Pids and return it
pi(_, P, List, Count) when Count > P -> List;
pi(T, P, List, Count) ->
Pid = spawn(pi, child, []),
Count2 = Count + 1,
pi(T,P, [Pid|List], Count2).


%start iterates through a list of Pids and sends a work order to each process
start(_, P, _, _, _, StaticList, Count) when Count > P -> await(StaticList, 0.0);
start(T, P, Tpart, Width, [Head|Tail], StaticList, Count) ->   
   Head ! {work, self(), P, Count, Tpart, Width},
   Count2 = Count + 1,
   start(T,P,Tpart,Width,Tail, StaticList, Count2).


%  Collects the partial sums from child processes. Print final output
await([], Final) -> io:format(" Final Sum: ~.8f \n", [(Final * 4.0)]);
await([Pid | Rest], Final) ->
    receive
        {done, Pid, Sum} ->
        Partial = Final + Sum,
        await(Rest, Partial)
    end.

Upvotes: 0

Views: 415

Answers (1)

dethtron5000
dethtron5000

Reputation: 10841

You cannot name Pids directly. You can take a process name, however, and register it using register/2. You should be careful, though, because the registered process name needs to be an atom and you could potentially fill up the atom table if you aren't careful. 

%Call to function
Pi = pi(T,P, [], 1, getName(1)), %list of Pids

% This is the main function that should return a list of Pid's with different names. 
pi(T, P, List, Count) when Count >= P -> List;
pi(T, P, List, Count) ->
Pid = spawn(pi, child, []), % I want to have name be: Pidx = ...
Count2 = Count + 1,
Name = getName(Count2),
register(Name,Pid),
pi(T,P, [Name|List], Count2).


%Helper method that returns an atom. I want to use this as a variable name in the main function.
getName(Count) ->
X = "Pid",
Y = integer_to_list(Count),
Name = X ++ Y,
list_to_atom(Name).

If you need a list of Pids, why name them at all? You could do something like this:

%Call to function
Pi = pi(T,P, [], 1, getName(1)), %list of Pids

% This is the main function that should return a list of Pid's with different names. 
pi(T, P, List, Count) when Count >= P -> List;
pi(T, P, List, Count) ->
Pid = spawn(pi, child, []), % I want to have name be: Pidx = ...
Count2 = Count + 1,
pi(T,P, [Pid|List], Count2).

This would return a list of Pids without the need of the other helper function.

Upvotes: 1

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