public int getWaitingTime(int rampUpInterval, int rampUpStep,
		                          int rampUpInitialThread, int rampUpInitialSleep, int threadNumber) {
			// 100 2 1 0 3   ==> 100
			if (threadNumber < rampUpInitialThread) {
				return 0;
			}
			int remained = (threadNumber - rampUpInitialThread);
			int threadStep = (remained / rampUpStep) + 1;
			return Math.max(rampUpInitialSleep + (threadStep * rampUpInterval), 0);
		}
The number of worker threads that have been created but not run to completion.
ngrinder-runtime/src/main/java/net/grinder/engine/process/GrinderProcess.java