code: void shutdown()
      {
          synchronized (this)
          {
              ivPoolCapacity = -1;
          }
  
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
              Tr.debug(tc, "shutdown : " + this);
  
          EntityManager em = ivPool.poll();
  
          while (em != null)
          {
              if (em.isOpen())
              {
                  em.close();
              }
              em = ivPool.poll();
          }
  
          synchronized (this)
          {
              ivPoolSize = 0;
          }
      }
docs: Prevents the pool from accepting any further EntityManager instances
  and closes all EntityManager instances currently in the pool. <p>