CODEWITHSUNDEEP
asynchronousdartyield
user3464741
user3464741

Reputation:

Slow asynchronous recursion in the dart language

I found asynchronous recursion in the dart language seems to be incredibly slow in the following code sample and I'd like to know why. 

import "dart:async";

Stream<int> rec(int z) async* {
  yield z;
  if (z > 0) yield* rec(z - 1);
}

void main() {
  Stream<int> stream = rec(10000);
  stream.listen((int x) {
    if (x % 1000 == 0) print(x);
  });
}

I'm testing this on the dart vm, so I can't believe that there is a timer involved as it is likely to be in a js vm in the browser.

If yield * were efficient enough I think it could serve as a replacement for trampolining a recursive function to avoid stack size limitation, too.

Upvotes: 0

Views: 323

Answers (1)

julemand101
julemand101

Reputation: 31229

Sounds like the following issue which has a long history. I recommend you to read the thread since I don't think I can make a resume here which would make it justice: https://github.com/dart-lang/sdk/issues/29189

I want to add that you example can also be written using sync* which are much faster but is of course not async:

Iterable<int> rec(int z) sync* {
  yield z;
  if (z > 0) yield* rec(z - 1);
}

void main() {
  final stream = rec(10000);
  stream.forEach((int x) {
    if (x % 1000 == 0) print(x);
  });
}

Upvotes: 0

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