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Level-triggered versus edge-triggered events – Create Your Own Event Queue
In a perfect world, we wouldn’t need to discuss this, but when working with epoll, it’s almost impossible to avoid having to know about the difference. It’s not obvious by reading the documentation, especially not if you haven’t had previous experience with these terms before. The interesting part of this is that it allows us…
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WHAT DOES #[REPR(PACKED)] DO? – Create Your Own Event Queue
The #[repr(packed)] annotation is new to us. Usually, a struct will have padding either between fields or at the end of the struct. This happens even when we’ve specified #[repr(C)]. The reason has to do with efficient access to the data stored in the struct by not having to make multiple fetches to get the…
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The ffi module – Create Your Own Event Queue-2
The last part of the code in this file is the Event struct: ch04/a-epoll/src/ffi.rs#[derive(Debug)]#[repr(C, packed)]pub struct Event { pub(crate) events: u32, // Token to identify event pub(crate) epoll_data: usize,}impl Event { pub fn token(&self) -> usize { self.epoll_data }} This structure is used to communicate to the operating system in epoll_ctl, and the operating system uses the same structure to communicate…
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The ffi module – Create Your Own Event Queue-1
Note The reason for doing file I/O in a thread pool is that there have historically been poor cross-platform APIs for non-blocking file I/O. While it’s true that many runtimes choose to relegate this task to a thread pool making blocking calls to the OS, it might not be true in the future as the…
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Is all I/O blocking? – Create Your Own Event Queue
Finally, a question that’s easy to answer. The answer is a big, resounding… maybe. The thing is that not all I/O operations will block in the sense that the operating system will park the calling thread and it will be more efficient to switch to another task. The reason for this is that the operating…
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IMPORTANT NOTE – Create Your Own Event Queue
By moving the concern of registering interests to a separate struct like this, users can call Registry::try_clone to get an owned Registry instance. This instance can be passed to, or shared through Arc<Registry> with, other threads, allowing multiple threads to register interest to the same Poll instance even when Poll is blocking another thread while…
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MIO – Create Your Own Event Queue-2
We’ll also use the std::io::Result type as our own Result type. It’s convenient since most errors will stem from one of our calls into the operating system, and an operating system error can be mapped to an io::Error type. There are two main abstractions over epoll. One is a structure called Poll and the other…
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MIO – Create Your Own Event Queue-1
mio describes itself as a “fast, low-level I/O library for Rust focusing on non-blocking APIs and event notification for building performance I/O apps with as little overhead as possible over the OS abstractions.” mio drives the event queue in Tokio, which is one of the most popular and widely used asynchronous runtimes in Rust. This…
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THE DELAY SERVER – Create Your Own Event Queue
This example relies on calls made to a server that delays the response for a configurable duration. In the repository, there is a project named delayserver in the root folder. You can set up the server by simply entering the folder in a separate console window and writing cargo run. Just leave the server running…
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Technical requirements – Create Your Own Event Queue
In this chapter, we’ll create a simple version of an event queue using epoll. We’ll take inspiration from mio (https://github.com/tokio-rs/mio), a low-level I/O library written in Rust that underpins much of the Rust async ecosystem. Taking inspiration from mio has the added benefit of making it easier to dive into their code base if you…
