Repository: tokio-rs/tokio
File: tokio-util/src/io/sync_bridge.rs (Rust)

Code before:
use std::io::{BufRead, Read, Seek, Write};
use tokio::io::{
    AsyncBufRead, AsyncBufReadExt, AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt, AsyncWrite,
    AsyncWriteExt,
};

/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
/// a [`tokio::io::AsyncWrite`] as a [`std::io::Write`].
///
/// # Alternatives
///
/// In many cases, there are better alternatives to using `SyncIoBridge`, especially if you
/// want to avoid blocking the async runtime. Consider the following scenarios:
///
/// ## Example 1: Hashing Data
///
/// When hashing data, using `SyncIoBridge` can lead to suboptimal performance and might not fully leverage the async capabilities of the system.
/// Instead, consider reading the data into memory and then hashing it, or processing the data in chunks.
///
/// ```rust, no_run
/// let mut data = Vec::new();
/// reader.read_to_end(&mut data).await?;
/// let hash = blake3::hash(&data);
/// ```
///
/// Or, for more complex cases:
///
/// ```rust, no_run
/// let mut data = vec![0; 64 * 1024];
/// loop {
///     let len = reader.read(&mut data).await?;
///     if len == 0 { break; }
///     hasher.update(&data[..len]);
/// }
/// let hash = hasher.finalize();
/// ```
///
/// ## Example 2: Compressing Data
///
/// When compressing data, avoid using `SyncIoBridge`` with non-async compression libraries, as it may lead to inefficient and blocking code.
/// Instead, use `async-compression`, which is designed to work with asynchronous data streams.
///
/// ```rust, no_run
/// use async_compression::tokio::write::GzipEncoder;
///
/// let mut encoder = GzipEncoder::new(writer);
/// tokio::io::copy(&mut reader, &mut encoder).await?;

Review comment (suggestion):
For async/await to work in the docs you actually also need a runtime since the doc test will be run by a synchronous main function by default. 

See this from tokio as an example:
```
    /// ```rust,no_run
    /// use std::error::Error;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let tokio_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await?;
    ///     let std_listener = tokio_listener.into_std()?;
    ///     std_listener.set_nonblocking(false)?;
    ///     Ok(())
    /// }
    /// ```
```

Code after:
use std::io::{BufRead, Read, Seek, Write};
use tokio::io::{
    AsyncBufRead, AsyncBufReadExt, AsyncRead, AsyncReadExt, AsyncSeek, AsyncSeekExt, AsyncWrite,
    AsyncWriteExt,
};

/// Use a [`tokio::io::AsyncRead`] synchronously as a [`std::io::Read`] or
/// a [`tokio::io::AsyncWrite`] synchronously as a [`std::io::Write`].
///
/// # Alternatives
///
/// In many cases, there are better alternatives to using `SyncIoBridge`, especially
/// if you want to avoid blocking the async runtime. Consider the following scenarios:
///
/// When hashing data, using `SyncIoBridge` can lead to suboptimal performance and
/// might not fully leverage the async capabilities of the system.
///
/// ### Why It Matters:
///
/// `SyncIoBridge` allows you to use asynchronous I/O operations in an synchronous
/// context by blocking the current thread. However, this can be inefficient because:
/// - **Inefficient Resource Usage**: `SyncIoBridge` takes up an entire OS thread,
///   which is inefficient compared to asynchronous code that can multiplex many
///   tasks on a single thread.
/// - **Thread Pool Saturation**: Excessive use of `SyncIoBridge` can exhaust the
///   async runtime's thread pool, reducing the number of threads available for
///   other tasks and impacting overall performance.
/// - **Missed Concurrency Benefits**: By using synchronous operations with
///   `SyncIoBridge`, you lose the ability to interleave tasks efficiently,
///   which is a key advantage of asynchronous programming.
///
/// ## Example 1: Hashing Data
///
/// The use of `SyncIoBridge` is unnecessary when hashing data. Instead, you can
/// process the data asynchronously by reading it into memory, which avoids blocking
/// the async runtime.
///
/// There are two strategies for avoiding `SyncIoBridge` when hashing data. When
/// the data fits into memory, the easiest is to read the data into a `Vec<u8>`
/// and hash it:
///
/// Explanation: This example demonstrates how to asynchronously read data from a
/// reader into memory and hash it using a synchronous hashing function. The
/// `SyncIoBridge` is avoided, ensuring that the async runtime is not blocked.
/// ```rust
/// use tokio::io::AsyncReadExt;
/// use tokio::io::AsyncRead;