How to avoid a race condition with _streamSubscription?.cancel();?

[stephane-archer]

I have a function foo that returns a Stream
I have a function onClick that cancels the previous StreamSubscription, calls foo, and adds a new listener

class bar {
StreamSubscription? _streamSubscription;
    Steam foo () {
     ...
    }
    void onClick () {
        await _streamSubscription?.cancel();
        var stream = foo();
        _streamSubscription = stream.listen((element) { print(element) })
    } 
}

from my understanding because of the await _streamSubscription?.cancel(); the user can run multiple times onClick and create a race condition, not all _streamSubscription is sure to be canceled