5 ms·

Well the above proves it's doable in C++ too. The issue hit upon is the time required to run a million of coroutines to completion (8s in the most optimized sce

Well the above proves it's doable in C++ too. The issue hit upon is the time required to run a million of coroutines to completion (8s in the most optimized scenario). Would Erlang/Elixir do better? I don't know, but I wouldn't be so sure.

rdtsc 7y ago
> Would Erlang/Elixir do better? I don't know, but I wouldn't be so sure. Pretty sure it can. Let's give it a try: #!/usr/bin/env escript %%! +P 2000000 %% run with ./spawn_n 1000000 -mode(compile). main([NStr]) -> N = list_to_integer(NStr), T0 = erlang:system_time(millisecond), Parent = self(), Waiter = spawn(fun() -> Parent ! {final_result, wait(N, 0)} end), spawn_n(N, Waiter), Res = receive {final_result, R} -> R end, Dt = erlang:system_time(millisecond) - T0, io:format("Done in ~p sec result:~p~n", [Dt/1000.0, Res]), ok. wait(0, Acc) -> Acc; wait(N, Acc) -> receive {result, R} -> ok end, wait(N - 1, Acc + R). spawn_n(0, _Waiter) -> ok; spawn_n(N, Waiter) -> spawn(fun() -> Waiter ! {result, 1} end), spawn_n(N - 1, Waiter). And it outputs: ./spawn_n 1000000 Done in 1.613 sec result:1000000 In summary, it started 1M processes, all with isolated heaps, pre-emptable, with only a few KB of stack size. They didn't execute much just sent their result to a collector process and then exited. All in about 5x as fast as C++.
- norswap 7y ago
  A most excellent answer :)
  - alexeiz 7y ago
    If the C++ code in comparison uses boost.coroutine2 library, then it's not surprising it performs poorly. Boost.coroutine2 library has an architectural flaw which causes it to throw (and then catch) an exception on coroutine completion. https://github.com/boostorg/coroutine2/issues/25 https://github.com/boostorg/coroutine2/issues/25

rdtsc 7y ago

> Would Erlang/Elixir do better? I don't know, but I wouldn't be so sure. Pretty sure it can. Let's give it a try: #!/usr/bin/env escript %%! +P 2000000 %% run with ./spawn_n 1000000 -mode(compile). main([NStr]) -> N = list_to_integer(NStr), T0 = erlang:system_time(millisecond), Parent = self(), Waiter = spawn(fun() -> Parent ! {final_result, wait(N, 0)} end), spawn_n(N, Waiter), Res = receive {final_result, R} -> R end, Dt = erlang:system_time(millisecond) - T0, io:format("Done in ~p sec result:~p~n", [Dt/1000.0, Res]), ok. wait(0, Acc) -> Acc; wait(N, Acc) -> receive {result, R} -> ok end, wait(N - 1, Acc + R). spawn_n(0, _Waiter) -> ok; spawn_n(N, Waiter) -> spawn(fun() -> Waiter ! {result, 1} end), spawn_n(N - 1, Waiter). And it outputs: ./spawn_n 1000000 Done in 1.613 sec result:1000000 In summary, it started 1M processes, all with isolated heaps, pre-emptable, with only a few KB of stack size. They didn't execute much just sent their result to a collector process and then exited. All in about 5x as fast as C++.

norswap 7y ago
A most excellent answer :)
- alexeiz 7y ago
  If the C++ code in comparison uses boost.coroutine2 library, then it's not surprising it performs poorly. Boost.coroutine2 library has an architectural flaw which causes it to throw (and then catch) an exception on coroutine completion. https://github.com/boostorg/coroutine2/issues/25 https://github.com/boostorg/coroutine2/issues/25