presto-main/src/main/java/io/prestosql/execution/SplitConcurrencyController.java/SplitConcurrencyController/splitFinished
class SplitConcurrencyController:    public void splitFinished(long splitThreadNanos, double utilization, int currentConcurrency)
    {
        checkArgument(splitThreadNanos >= 0, "nanos is negative");
        checkArgument(isFinite(utilization), "utilization must be finite");
        checkArgument(utilization >= 0, "utilization is negative");
        checkArgument(currentConcurrency >= 0, "currentConcurrency is negative");

        if (threadNanosSinceLastAdjustment >= adjustmentIntervalNanos || threadNanosSinceLastAdjustment >= splitThreadNanos) {
            if (utilization > TARGET_UTILIZATION && targetConcurrency > 1) {
                threadNanosSinceLastAdjustment = 0;
                targetConcurrency--;
            }
            else if (utilization < TARGET_UTILIZATION && currentConcurrency >= targetConcurrency) {
                threadNanosSinceLastAdjustment = 0;
                targetConcurrency++;
            }
        }
    }