Polling, as the name suggests, involves the client periodically checking a service for any new events. This is often the least desirable means of asynchronous communication as polling increases system utilization and becomes difficult to scale. Yet, it might be the only feasible solution in a legacy system.
A polling system works as follows:
- The client calls a service
- The call returns immediately with new events or the status of the task
- The client waits and repeats step two at periodic intervals
There might be some degree of synchronous delay while retrieving the status of the service. The client might be blocking until the response arrives. Hence, it is sometimes referred to as busy-waiting.