I want to share an anecdote of confusing programming language features as a caution to my fellow programmers.
Reviewing our application logs, I noticed that the API requests were interspersed with pauses of irregular durations. The interval between each successful request is supposed to be fixed; and the interval between each failed request, exponentially growing up to a configured maximum. For example, after the first failure, the application pauses for 5 seconds; after the second, 10 seconds; after the third, 20 seconds; and so on. However, the logs showed intervals of 15 seconds, 30 seconds, 60 seconds, then 0 second—this was odd, especially the last 0 second.
This behaviour remained a mystery even after a colleague helped me look for errors in our C# code. We reviewed this line of code together but found nothing wrong; it clearly showed that on every retry the base interval was doubled.
int tmp = RetryIntervalInMs * (2 ^ retryCounter);By coincidence, I needed the same calculation of intervals in my hobby embedded project. As I started to write the code that evening, I made an epiphanic realisation.
In our C# code, we had used the ^ operator, interpreting it as raised to the power of. This is true in some languages – BASIC, for example – but not in C#, where it is actually the operator for XOR. I was amazed that this mistake escaped our scrutiny..
Once we had identified the cause, it was easy to fix the error by using the correct library method Math.Pow(int, int).
int tmp = RetryIntervalInMs * (int)Math.Pow(2, retryCounter);