Polling is the process where the computer or controlling device waits for an external device to check for its readiness or state, often with low-level hardware. For example, when a printer is connected via a parallel port, the computer waits until the printer has received the next character. Source Wikipedia
The basic polling includes polling for a single polling-job. The Poll API returns a single PollDefinition instance that is used for executing and initiating the poll.
Asynchronous polling includes executing more than one polling-job in parallel. The Poll API returns a list or collection of the PollDefinition instances that are executed in parallel.
The entry criteria is a condition that is evaluated to determine whether to initiate the polling-job or not. It functions like setting an initial delay to the polling-job (it's an alternative to initial-delay), however, rather than a fixed time wait, this criteria is considered a pre-polling-job which is iteratively executed at polling-intervals, similar to the primary-polling-job until the entry-criteria is met.
PS: The entry criteria also uses the same time-out value to avoid endless polling. Also, the captured result of the pre-polling-job is not returned to the consumer
holdUntil(Predicate<? super T> entryCriteria, Supplier<? super T> action)
The exit-criteria is the condition that is evaluated by the primary polling-job (executed iteratively at polling-intervals) to determine when to exit the iterative process. If the exit-criteria is not met before the polling time-out is reached, the polling-job is aborted and is said to be timed-out.
until(Predicate<? super T> exitCriteria, Supplier<? super T> action)
The maximum time until which the polling should continue unless an exit-criteria is not. The result returned has the isTimedOut flag as true in such a case.
PS: This time-out won't be reached if the exit-criteria is met earlier
pollFor(Integer timeOut, TimeUnit timeOutUnit)
Polling iterations is an alternative to Polling time-out, where instead of waiting for a maximum time-out, a specific number of iterations would be executed unless an exit-criteria is met.
pollFor(Integer pollIterations)
The time-interval at which the job should be executed/queried to determine if it meets the exit-criteria or not.
every(Integer timeInterval, TimeUnit timeIntervalUnit)
Polling initial delay is an initial wait before the 1st polling-job is executed/queried. This is an alternative to entry-criteria.
holdFor(Integer intialDelay, TimeUnit intialDelayUnit)
####Synchronous Polling
Poll using a