         let index = Int(arc4random_uniform(UInt32(senders.count)))
         senders[index] <- i
       }
+      NSThread.sleepForTimeInterval(sleepInterval > 0 ? sleepInterval : 1e-6)
       for sender in senders { sender.close() }
     }
 

//    syncprint("\(i) messages received")
    syncprintwait()

    XCTAssert(i == iterations, "incorrect number of messages received")
  }

  func testPerformanceSelectBufferedSender()

      if let message: Int = selection.getData() { i++ }
    }

    syncprintwait()
    
    XCTAssert(i == iterations, "Received \(i) messages; expected \(iterations)")
  }

  func testPerformanceSelectBufferedReceiver()
