/**
* @return The number of operations the test managed to execute per second with the given number of threads.
*/
private double performRound(int threads) {
long initialOperationCount = operationCount;
StopWatch stopWatch = StopWatch.start();
startThreads(threads);
sleep();
stopThreads();
double secondsEllapsed = stopWatch.secondsEllapsed();
double operationsPerSecond = (operationCount - initialOperationCount) / secondsEllapsed;
out("\nMemory used: " + Runtime.getRuntime().totalMemory());
subject.reportResourcesUsed(System.out);
out("Seconds ellapsed: " + secondsEllapsed);