Create list across many processes in Erlang

问题

Ok, I am even having a hard time thinking of how to describe what I need. But it is really quite simple. I want to spawn n number of processes that generate n number of IDs. I have this working with some simple recursion and printing to the terminal. Where I am struggling is creating a list accessible to each of these spawned processes where I can accumulate the ids. then, when the processes are complete, I need to print-out any duplicates.

I tried a few different options with ets tables and it always prints a list of nothing. I presume because I get to the printing function before the processes have completed? I know I am thinking of this wrong but would greatly appreciate a nudge in the right direction.

回答1:

You need to synchronize your main process with the spawned processes. You can do that by sending a message from each of the id generator processes to the main, and the latter would wait for all the processes to report.

master(N) ->
   %% we need a pid of this process for the slaves to send messages to
   Self = self(),

   %% spawn slave processes and save their pids
   Pids = [spawn(fun() -> slave(Self) end || lists:seq(1, N)],

   %% receive id message from each of the slave processes
   Ids = [recv_id(Pid) || Pid <- Pids],

   %% do whatever we want with the data here
   find_duplicates(Ids).

slave(Master) ->
   Id = mk_id(),

   %% send a message to the master
   Master ! {id, self(), Id}.

recv_id(Pid) ->
   receive
      {id, Pid, Id} -> Id
   end.

mk_id() -> ...
find_duplicates(Ids) -> ...

来源：https://stackoverflow.com/questions/19823512/create-list-across-many-processes-in-erlang

标签

erlang