Threading.md

use std::thread;
use std::time::Duration;

thread::spawn(move || loop {
    println!("Hi from Ted the thread. I print to stdout every 1_000 ms.");
    thread::sleep(Duration::from_millis(1_000));
});

mpsc

let (tx_to_worker, rx_to_worker) = mpsc::channel::<Vec<u8>>();
let (tx_from_worker, rx_from_worker) = mpsc::channel::<Vec<u8>>();

Let me break down this channel creation code:

In Rust, mpsc stands for "Multiple Producer, Single Consumer" and provides a way for threads to communicate by sending messages to each other. Let's analyze each part:

// First channel: Main thread -> Worker thread
let (tx_to_worker, rx_to_worker) = mpsc::channel::<Vec<u8>>();
// tx_to_worker: Sender - Main thread uses this to send data
// rx_to_worker: Receiver - Worker thread uses this to receive data

// Second channel: Worker thread -> Main thread
let (tx_from_worker, rx_from_worker) = mpsc::channel::<Vec<u8>>();
// tx_from_worker: Sender - Worker thread uses this to send data
// rx_from_worker: Receiver - Main thread uses this to receive data

Think of it like two one-way pipes:

1. First pipe (tx_to_worker -> rx_to_worker):

   • Main thread writes data using tx_to_worker.send()
   • Worker thread reads data using rx_to_worker.recv()

2. Second pipe (tx_from_worker -> rx_from_worker):

   • Worker thread writes data using tx_from_worker.send()
   • Main thread reads data using rx_from_worker.recv()

Here's a visual representation:

flowchart LR
    M[Main Thread] --> |tx_to_worker| W[Worker Thread]
    W --> |tx_from_worker| M
    
    subgraph Channel 1
    tx_to_worker --- rx_to_worker
    end
    
    subgraph Channel 2
    tx_from_worker --- rx_from_worker
    end

Loading

The Vec<u8> part specifies that we're sending vectors of bytes through these channels. For example:

// In main thread
tx_to_worker.send(vec![1, 2, 3])?; // Sends bytes to worker

// In worker thread
let received = rx_to_worker.recv()?; // Receives those bytes
// received would be vec![1, 2, 3]

// Worker can then send back data
tx_from_worker.send(vec![4, 5, 6])?;

// Main thread receives it
let response = rx_from_worker.recv()?; // Gets vec![4, 5, 6]

This setup allows for safe, concurrent communication between the threads. Some key points:

• Each channel is one-way only
• Channels are thread-safe by design
• If all Senders or all Receivers are dropped, the channel is closed
• You can clone Senders (tx) but not Receivers (rx) - that's why it's "Multiple Producer, Single Consumer"

Questions about mpsc

1. Channel Sending Efficiency:

• By default, channels pass ownership of the data by moving it (not copying)
• For Vec<u8>, only the vector's metadata (pointer, length, capacity) is moved through the channel - the actual heap data isn't copied
• However, if multiple threads need access to large data, consider using Arc to share ownership:

// Instead of sending large data directly
tx.send(huge_vector)?;

// You could send a shared reference
let shared_data = Arc::new(huge_vector);
tx.send(Arc::clone(&shared_data))?;

2. Rust provides several ways to handle channel reception:

use std::sync::mpsc::{self, TryRecvError, RecvTimeoutError};
use std::time::Duration;

// 1. Blocking recv() - waits indefinitely
let value = rx.recv()?; // Blocks until data arrives

// 2. Non-blocking try_recv() - returns immediately
match rx.try_recv() {
    Ok(value) => println!("Got value: {:?}", value),
    Err(TryRecvError::Empty) => println!("No data available"),
    Err(TryRecvError::Disconnected) => println!("Channel closed"),
}

// 3. Timeout-based recv_timeout()
match rx.recv_timeout(Duration::from_secs(1)) {
    Ok(value) => println!("Got value: {:?}", value),
    Err(RecvTimeoutError::Timeout) => println!("Timed out"),
    Err(RecvTimeoutError::Disconnected) => println!("Channel closed"),
}

// 4. Iterator-based approach for multiple values
for received in rx.iter() {
    println!("Got: {:?}", received);
}

// 5. Using select! macro (requires tokio or similar async runtime)
use tokio::select;

async fn handle_channels(rx1: mpsc::Receiver<i32>, rx2: mpsc::Receiver<String>) {
    loop {
        select! {
            val = rx1.recv() => println!("Got number: {:?}", val),
            msg = rx2.recv() => println!("Got message: {:?}", msg),
        }
    }
}

If you need more sophisticated async handling, you might want to consider using Tokio's channels instead of std::sync::mpsc. Tokio provides async versions of channels with additional features:

use tokio::sync::mpsc;

async fn example() {
    let (tx, mut rx) = mpsc::channel(32); // With buffer size

    // Sender task
    tokio::spawn(async move {
        tx.send(42).await.unwrap();
    });

    // Receiver task
    while let Some(value) = rx.recv().await {
        println!("got = {}", value);
    }
}

For your specific serial port communication case, you might want to consider a hybrid approach:

use std::sync::{mpsc, Arc};
use std::time::Duration;

pub struct SerialComms {
    tx: mpsc::Sender<Vec<u8>>,
    rx: mpsc::Receiver<Vec<u8>>,
    shared_buffer: Arc<Vec<u8>>, // For large, shared data
}

impl SerialComms {
    pub fn receive_with_timeout(&self, timeout: Duration) -> Result<Vec<u8>, RecvTimeoutError> {
        self.rx.recv_timeout(timeout)
    }
    
    pub fn try_receive(&self) -> Result<Vec<u8>, TryRecvError> {
        self.rx.try_recv()
    }
    
    // For handling large shared data
    pub fn send_shared(&self, data: Arc<Vec<u8>>) -> Result<(), mpsc::SendError<Arc<Vec<u8>>>> {
        self.tx.send(Arc::clone(&data))
    }
}

This gives you flexibility in how you want to handle the communication:

• Use non-blocking try_receive() for polling
• Use timeouts for bounded waiting
• Share large data efficiently with Arc
• Could be extended to use async/await if needed