[Bug Report] Slowness when multiple threads try to call messagingClient.send(deviceId, message, 10000) continuously

**Java Iothub Lib:**
iot-service-client: 2.1.6

**Azure IotHub Units:**
S1: 100

**Observation:**
Currently we are re-using same Messaging client by multiple threads, Just in case there are some issues connecting to IotHub, we close and open a new one. And re-use the same.

When there is a demand to send lot of iothub messages continuously, There is a sudden drop on the speed of sending iothub messages.

Is there a way to enhance this speed when there is a high demand to send lot of iothub messages **(however the number of messages are under the max throttle limit of Iothub Units, in our case there are approx. S1-100 Units.**) ?

Is it like using same Messaging Client by Multiple threads slow down the speed or can messaging client be used with a pool of connections and Threads can borrow them and use when needed. Instead of having just 1 client, by using pool we can have a little more number of clients like 5 or 10?

Any suggestions or comments would be greatly appreciated.