说明

By default when events are polled for, blocking will occur (at the PHP level) until the first event can be returned: Setting blocking mode to false will cause poll to return control if the first target polled is not ready.

This differs from setting a timeout of 0 with parallel\Events::setTimeout(), since a timeout of 0, while allowed, will cause an exception to be raised, which may be extremely slow or wasteful if what is really desired is non-blocking behaviour.

A non-blocking loop effects the return value of parallel\Events::poll(), such that it may be null before all events have been processed.

Shall set blocking mode