Comment by jpollock

If we change the code, getting rid of if statements, it's easier to see what happens by removing if's.

I've changed BucketReduction to be a pair, and fixed the strange behavior on error. Swapping "fromBurst" and "auto_replenish" would reduce the number of throttling events. This solution does have more branches than the original, hence readability vs performance. It's still not exception safe, auto_replenish could throw and leave the state undefined.

    BucketReduction reduce(long tokens) {
        long fromBurst = min(tokens, burst);
        burst -= fromBurst;
        tokens -= fromBurst;

        if (tokens > budget) {
            auto_replenish();
        }

        long fromBudget = min(tokens, budget);
        budget -= fromBudget;
        tokens -= fromBudget;

        long totalConsumed = fromBurst + fromBudget;
        if (tokens == 0) {
            return new BucketReduction(Success, totalConsumed);
        }

        if (totalConsumed + tokens > size) {
            return new BucketReduction(OverConsumption, totalConsumed);
        }

        return new BucketReduction(Failure, totalConsumed);
    }