如何在这种“时间重置”后解决比赛条件？

Question

Input is an observable that produces a value each time a problem occurs.

As output I want an observable that produces a value if problems exist for a longer time. In other words I want to "reset" the output observable (not produce values) if the last problem is outdated.

My solution:

// first get an observable producing statusOk values (true = ok, false = not ok)
var okStatusObservable = input.Select(_ => true).Throttle(longerTime)
                  .Merge(input.Select(_ => false));


// we only want event if statusOk=false for a longer time
var outputObservable = okStatusObservable
                  .DistinctUntilChanged() // only changes
                  .Throttle(evenLongerTime) // wait for stable status
                  .Where(_ => _ == false); // only interested in bad status

I think the okStatusObservable might contain a race condition: If input receives events at time interval of exactly longerTime and second merge part ( Select / false ) would produce a boolean before the first part ( Select + Throttle / true ) then this would result in okStatus to be true 99.9% of the time where the opposite would be correct.

(PS: to have status value from beginning, we might add .StartWith(true) but that doesn't matter regarding race condition.)

Answer 1

A cleaner way to do the first observable is as follows:

var okStatusObservable2 = input
    .Select(_ => Observable.Return(true).Delay(longerTime).StartWith(false))
    .Switch();

Explanation: For each input message, produce an observable that starts with a false, and after longerTime produces a true. The Switch means that if you have a new observable, just switch to it, which would exclude the all-clear true at the end.

For your second observable, unless longerTime differs between the two observables, every first false in the first observable will result in a false in the second. Is that your intention?

Also, your Where is messed up (should be .Where(b => !b) or .Where(b => b == false) . .Where(_ => false) will always evaluate to false returning nothing.

Other than that, I think your solution is sound.