Epore - Learning how to use epoll to Event Queue for non-blocking I/O

Files Structure

• ffi.rs: This module will contain the code related to the syscalls we need to communicate with the host operating system.
• main.rs: This is the example program itself
• poll.rs: This module contains the main abstraction, which is a thin layer over epoll

Overview

• Poll: Struct to interface with the OS's event notification system aka event queue (io_uring, epoll, kqueue, IOCP).

  • new(): To create a new interface to OS's event queue. Similar to epoll_create
  • registry(): Returns a reference to the registry that we can use to register interest to be notified about new events. Similar to int epoll_ctl(int epfd, int op, int fd, struct epoll_event *_Nullable event);
  • poll(): blocks the thread it's called on until an event is ready or its times out, whichever occurs first.

• Registry: Struct to register interest in a certain Event.

• Token: Using Token to track which TcpStream socket generated the event.

Sample Usage

let queue = Poll::new().unwrap();
let id = 1;

// register interest in events on a TcpStream
queue.registry().register(&stream, id, ...).unwrap();

// store the to be tracked events
let mut events = Vec::with_capacity(1);

// This will block the current thread
queue.poll(&mut events, None).unwrap();
//...data is ready on one of the tracked streams

How To Run

• Get and run the delayServer from Packt's Asynchronous-Programming-in-Rust repo.

• In another window, run this program with cargo run.

Notes

Registry and Poll Relationship

We can see that the struct Poll has an internal struct Registry inside of it. By moving the struct Registry inside of the Poll struct, we can call Registry::try_clone() to get an owned Registry instance.

Therefore, we can pass the Registry to other threads with Arc, allowing multiple threads to register their interest to the same Poll instance even when Poll is blocking another thread while waiting for new events to happen in Poll::poll

Poll::poll() requires exclusive access since it takes a &mut self, so when we're waiting for events in Poll::poll(), there is no way to register interest from a different thread at the same time if we rely on using Poll to register.