Determines information necessary to poll this main loop.
You should be careful to pass the resulting
fds array and its length
fds.length as is when calling
check, as this function relies on assumptions made when the array is filled.
You must have successfully acquired the context with acquire before you may call this function.
a MainContext (if null, the global-default main context will be used)
maximum priority source to check
location to store timeout to be used in polling
location to store PollFD records that need to be polled.
the number of records actually stored in