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What are the concepts of Poll, Epoll and Future in high concurrency? in order to solve this problem, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible method.

There are several important concepts in high concurrency: Poll, Epoll, Future.

Future is not a mainstream implementation, but the concept of Future and Poll is so important that we must put it at the beginning, so we first focus on Rust, because Rust is more complete for Future implementation than Go and Java, and the feature support is also thorough. So the following code takes Rust as an example.

Simply put, Future is not a value, but a value type, a value type that can only be obtained in the future. The Future object must implement the std::future:: future interface in the Rust standard library. The output Output of Future is a value that cannot be generated until Future is complete. In Rust, Future calls Future::poll through the manager to promote the operation of Future. Future is essentially a state machine and can be nested. Let's take a look at the following example. In the main function, we instantiate MainFuture and call .await, while MainFuture, in addition to migrating between several states, calls a Delay Future to achieve nesting of Future.

MainFuture takes the State0 state as its initial state. When the scheduler calls the poll method, MainFuture tries to improve its state as much as possible. If the future is complete, Poll::Ready is returned, and if the MainFuture is not completed, it is because the DelayFuture it is waiting for does not reach the Ready state, then Pending is returned at this time. When the scheduler receives the Pending result, it will put the MainFuture back into the queue to be scheduled, and later call the Poll method again to promote the execution of the Future. The details are as follows:

Usestd:: future::Future;use std::pin::Pin;usestd::task:: {Context, Poll}; usestd::time:: {Duration, Instant}; struct Delay {when: Instant,} impl Future forDelay {type Output = & 'static str; fn poll (self: Pin, cx:&mut Context {if Instant::now () > = self.when {println! ("Hello world") Poll::Ready ("done")} else {cx.waker (). Wake_by_ref (); Poll::Pending}} enum MainFuture {State0, State1 (Delay), Terminated,} impl Future forMainFuture {type Output = (); fn poll (mut self: Pin,cx: & mut Context

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