title: Gatling: Keep fixed number of users/requests at any instant
body: <p>how can we keep fixed number of active concurrent users/requests at time for a scenario.</p>
  
  <p>I have an unique testing problem where I am required to do the performance testing of services with fixed number of request at a given moment for a given time periods like 10 minutes or 30 minutes or 1 hour.</p>
  
  <p>I am not looking for per second thing, what I am looking for is that we start with N number of requests and as any of request out of N requests completes we add one more so that at any given moment we have N concurrent requests only.</p>
  
  <p>Things which I tried are <code>rampUsers(100) over 10 seconds</code> but what I see is sometimes there are more than 50 users at a given instance. </p>
  
  <p><code>constantUsersPerSec(20) during (1 minute)</code> also took the number of requests t0 50+ for sometime.</p>
  
  <p><code>atOnceUsers(20)</code> seems related but I don't see any way to keep it running for given number of seconds and adding more requests as previous ones completes.</p>
  
  <p>Thankyou community in advance, expecting some direction from your side.</p>