docs: add docs for poll-io (#311)

docs/en/poll-io.md

@@ -0,0 +1,99 @@
+---
+title: Poll IO Support
+date: 2024-10-21 17:00:00
+author: ihciah
+---
+
+Poll IO is a new IO Driver capability provided in Monoio, which allows for good compatibility with components that use poll-style IO interfaces.
+
+By default, for example, `TcpStream` will implement the `AsyncReadRent`/`AsyncWriteRent` traits. These traits require ownership transfer during read and write operations to ensure memory safety when using io-uring as the driver. Code written this way can run directly without modification, leveraging Monoio’s internal fallback mechanism, regardless of whether the runtime environment supports io-uring or not. Since this IO trait is completion-based, we refer to IOs implementing this type of trait as `CompIo` in the following text.
+
+However, many components still use mainstream poll-style IO interfaces, including `tokio::io::AsyncRead`, `async_std::io::Read`, and components like hyper, which abstract Read/Write interfaces to support multiple runtimes. Converting between these different poll-style IO interfaces is relatively easy. Since this IO trait is a synchronous attempt executed when ready, we will refer to it as `PollIo` in the following text.
+
+To support these components, Monoio provides:
+
+1. `IntoPollIo`/`IntoCompIo`: for converting between `PollIo` and `CompIo`.
+2. Structures like `TcpStreamPoll`, which implement `tokio::io::AsyncRead/AsyncWrite`.
+
+## Usage Example
+
+1. First, ensure that your project enables the `poll-io` feature when adding `monoio` as a dependency(Requires version 0.2.2 or higher):
+
+    ```toml
+    [dependencies]
+    monoio = { version = "0.2.4", features = ["poll-io"] }
+    ```
+
+2. Import and use `IntoPollIo` to convert `CompIo` to `PollIo`.
+
+    In the example below, we will start a listener, convert accepted connections to `PollIo`, and then use tokio’s `AsyncRead`/`AsyncWrite` traits for reading and writing.
+
+    ```rust
+    use monoio::{
+        io::{
+            // Here AsyncReadExt and AsyncWriteExt are re-exported from and equivalent with tokio
+            poll_io::{AsyncReadExt, AsyncWriteExt},
+            IntoPollIo,
+        },
+        net::{TcpListener, TcpStream},
+    };
+
+    #[monoio::main(driver = "fusion")]
+    async fn main() {
+        let listener = TcpListener::bind("127.0.0.1:50002").unwrap();
+        println!("listening");
+        loop {
+            let incoming = listener.accept().await;
+            match incoming {
+                Ok((stream, addr)) => {
+                    println!("accepted a connection from {addr}");
+                    monoio::spawn(echo(stream));
+                }
+                Err(e) => {
+                    println!("accepted connection failed: {e}");
+                    return;
+                }
+            }
+        }
+    }
+
+    async fn echo(stream: TcpStream) -> std::io::Result<()> {
+        // Convert completion-based io to poll-based io(which impl tokio::io)
+        let mut stream = stream.into_poll_io()?;
+        let mut buf: Vec<u8> = vec![0; 1024];
+        let mut res;
+        loop {
+            // read
+            res = stream.read(&mut buf).await?;
+            if res == 0 {
+                return Ok(());
+            }
+
+            // write all
+            stream.write_all(&buf[0..res]).await?;
+        }
+    }
+    ```
+
+    More examples can be found in [examples/h2_client.rs](../../examples/h2_client.rs) and [examples/h2_server.rs](../../examples/h2_server.rs).
+
+## Underlying Implementation
+
+Poll IO capability is implemented based on epoll over io-uring:
+
+1. If the current driver is a legacy driver (e.g., on macOS or lower version Linux platforms), Poll IO capability can be provided directly;
+2. If the current driver is an io-uring driver, enabling this feature will add an epoll fd to io-uring, and the Poll IO capability will be provided via this epoll fd.
+
+When we convert a `CompIo` to `PollIo`, if running on io-uring, it is necessary to obtain the epoll fd maintained within and register the file descriptor corresponding to the `CompIo` with it. This way, when CompIo becomes ready, the runtime can detect the readiness of the epoll fd via io-uring’s completion notifications and call `epoll_wait(0)` to get all the ready events on it.
+
+If the current driver is not io-uring, the conversion has almost no cost.
+
+On Linux platforms, the relationship between IO traits and underlying drivers is as follows:
+
+1. `CompIo` -> `io-uring` / `epoll`
+2. `PollIo` -> `epoll` / `epoll over io-uring`
+
+## Notes
+
+1. This feature provides good support for libraries such as hyper and h2. However, to fully utilize io-uring’s capabilities, it is recommended to use CompIo-style IO interfaces (`AsyncReadRent`, `AsyncWriteRent`) in hot paths;
+2. This feature has undergone extensive production environment validation, but some components may not yet support the `IntoPollIo`/`IntoCompIo` conversion capabilities. Please feel free to report any related issues.

docs/zh/poll-io.md

@@ -0,0 +1,98 @@
+---
+title: Poll IO 支持
+date: 2024-10-21 17:00:00
+author: ihciah
+---
+
+Poll IO 是 Monoio 中提供的一种新的 IO Driver 相关能力，借助这个能力可以良好地兼容使用 poll 风格 IO 接口的组件。
+
+默认情况下，例如 `TcpStream` 会实现 `AsyncReadRent`/`AsyncWriteRent` trait。这种 trait 要求读写时转移所有权，因为只有这样才能在使用 io-uring 作为 driver 时保证内存安全。无论运行环境是否支持 io-uring，以该方式编写的代码都可以在不做任何修改的情况下借助 Monoio 内部的 fallback 机制直接运行。由于这种 IO trait 是面向完成通知的，下文将实现该类 trait 的 IO 称之为 `CompIo`。
+
+但是，仍有大量的组件使用当前主流的 poll 风格 IO 接口，包括 `tokio::io::AsyncRead`，`async_std::io::Read`，以及 hyper 等组件为了支持多种 runtime 抽象出的 Read/Write 接口。在这些不同的 poll 风格 IO 接口之间转换是非常容易的。由于这种 IO trait 是在就绪是同步尝试执行的，下文中称之为 `PollIo`。
+
+为了支持这些组件，Monoio 提供了：
+
+1. `IntoPollIo`/`IntoCompIo`：在 `PollIo` 和 `CompIo` 之间转换。
+2. `TcpStreamPoll` 等结构，实现 `tokio::io::AsyncRead/AsyncWrite`。
+
+## 使用例子
+
+1. 首先请确保你的项目在引入 `monoio` 时开启了 `poll-io` feature（需要 0.2.2 及以上版本）：
+
+    ```toml
+    [dependencies]
+    monoio = { version = "0.2.4", features = ["poll-io"] }
+    ```
+
+2. 引入并使用 `IntoPollIo` 来将 `CompIo` 转换为 `PollIo`。
+    在下面的例子中，我们将启动一个 Listener，并将 accept 到的连接转换为 PollIo，之后使用 tokio 的 `AsyncRead`/`AsyncWrite` trait 进行读写。
+
+    ```rust
+    use monoio::{
+        io::{
+            // Here AsyncReadExt and AsyncWriteExt are re-exported from and equivalent with tokio
+            poll_io::{AsyncReadExt, AsyncWriteExt},
+            IntoPollIo,
+        },
+        net::{TcpListener, TcpStream},
+    };
+
+    #[monoio::main(driver = "fusion")]
+    async fn main() {
+        let listener = TcpListener::bind("127.0.0.1:50002").unwrap();
+        println!("listening");
+        loop {
+            let incoming = listener.accept().await;
+            match incoming {
+                Ok((stream, addr)) => {
+                    println!("accepted a connection from {addr}");
+                    monoio::spawn(echo(stream));
+                }
+                Err(e) => {
+                    println!("accepted connection failed: {e}");
+                    return;
+                }
+            }
+        }
+    }
+
+    async fn echo(stream: TcpStream) -> std::io::Result<()> {
+        // Convert completion-based io to poll-based io(which impl tokio::io)
+        let mut stream = stream.into_poll_io()?;
+        let mut buf: Vec<u8> = vec![0; 1024];
+        let mut res;
+        loop {
+            // read
+            res = stream.read(&mut buf).await?;
+            if res == 0 {
+                return Ok(());
+            }
+
+            // write all
+            stream.write_all(&buf[0..res]).await?;
+        }
+    }
+    ```
+
+    更多例子可以参考 [examples/h2_client.rs](../../examples/h2_client.rs) 和 [examples/h2_server.rs](../../examples/h2_server.rs)。
+
+## 底层实现
+
+Poll IO 能力基于 epoll over io-uring 实现：
+
+1. 如果当前 driver 为 Legacy Driver（例如，在 macOS，或低版本 Linux 平台上），那么可以直接对外提供 Poll IO 能力；
+2. 如果当前 driver 为 io-uring Driver，那么开启本 feature 后，会在 io-uring 上添加一个 epoll fd，并基于这个 epoll fd 对外提供 Poll IO 能力。
+
+当我们将一个 `CompIo` 转换为 `PollIo` 时，如果当前运行在 io-uring 上，则需要取得在其中维护的 epoll fd 并向其注册该 `CompIo` 对应的文件描述符。这样，当 `CompIo` 就绪时，Runtime 就可以通过 io-uring 的完成通知感知到 epoll fd 就绪，并执行 `epoll_wait(0)` 以获得所有在其上的就绪事件。
+
+如果当前 driver 非 io-uring，则转换操作是几乎没有成本的。
+
+在 Linux 平台上，IO trait 与底层 driver 对应关系：
+
+1. `CompIo` -> `io-uring` / `epoll`
+2. `PollIo` -> `epoll` / `epoll over io-uring`
+
+## 注意事项
+
+1. 使用该功能可以良好地支持 hyper、h2 等库；但为了充分利用 io-uring 的能力，建议在 hot path 上使用 `CompIo` 风格的 IO 接口（`AsyncReadRent`、`AsyncWriteRent`）；
+2. 该功能已经过较大规模的生产环境验证，但当前可能有部分组件没有支持 `IntoPollIo`/`IntoCompIo` 转换能力，欢迎汇报相关问题；