make display thread dedicated, move to display.rs

display thread should be dedicated to not steal resources from tokio

src/api.rs

@@ -1,4 +1,4 @@
-use crate::display::EInkPanel;
+use crate::display::{create_display_thread, EInkPanel};
 use crate::dither::{DitherMethod, DitheredImage};
 use crate::eink::Palette;
 use axum::async_trait;
@@ -10,10 +10,10 @@ use image::{ImageReader, RgbImage};
 use std::io::Cursor;
 use std::str;
 use std::str::FromStr;
+use std::sync::mpsc;
 use std::sync::Arc;
+use std::thread::JoinHandle;
 use std::time::Duration;
-use tokio::sync::mpsc::{self, Receiver, Sender};
-use tokio::task::JoinHandle;
 use tracing::{error, info, instrument};
 
 #[derive(thiserror::Error, Debug)]
@@ -24,18 +24,17 @@ pub enum ApiError {
 
 #[derive(Clone)]
 pub struct AppState {
-    display_channel: Sender<DisplaySetCommand>,
+    display_channel: mpsc::Sender<Box<DitheredImage>>,
     display_task: Arc<JoinHandle<()>>,
 }
 
 impl AppState {
     #[must_use]
     pub fn new(disp: Box<dyn EInkPanel + Send>) -> Self {
-        let (tx, rx) = mpsc::channel(2);
+        let (handle, tx) = create_display_thread(disp);
-        let task = tokio::spawn(display_task(rx, disp));
         Self {
             display_channel: tx,
-            display_task: Arc::new(task),
+            display_task: Arc::new(handle),
         }
     }
 }
@@ -65,25 +64,6 @@ where
     }
 }
 
-#[derive(Debug)]
-pub struct DisplaySetCommand {
-    img: Box<DitheredImage>,
-}
-
-#[instrument(skip_all)]
-pub async fn display_task(
-    mut rx: Receiver<DisplaySetCommand>,
-    mut display: Box<dyn EInkPanel + Send>,
-) {
-    while let Some(cmd) = rx.recv().await {
-        info!("Got a display set command");
-        if let Err(e) = display.display(&cmd.img) {
-            error!("Error displaying command {e}");
-        }
-        info!("Done setting display");
-    }
-}
-
 /// API routes for axum
 /// Start with the basics: Send an image, crop it, dither, and upload.
 /// we defer the upload to a separate task.
@@ -163,10 +143,7 @@ async fn set_image(
         let mut dither = img_req.dither_method.get_ditherer();
         dither.dither(&img_req.image, &mut buf);
     }
-    let cmd = DisplaySetCommand { img: Box::new(buf) };
+    ctx.display_channel.send(Box::new(buf))?;
-    ctx.display_channel
-        .send_timeout(cmd, Duration::from_secs(10))
-        .await?;
     Ok(StatusCode::OK)
 }
 

src/display.rs

@@ -1,14 +1,16 @@
+// Manages display hardware
+use crate::dither::DitheredImage;
+use anyhow::Result;
 use epd_waveshare::{epd7in3f::Epd7in3f, prelude::WaveshareDisplay};
+use linux_embedded_hal::gpio_cdev::{Chip, LineRequestFlags};
 use linux_embedded_hal::spidev::SpiModeFlags;
 use linux_embedded_hal::spidev::SpidevOptions;
 use linux_embedded_hal::{CdevPin, Delay, SpidevDevice};
+use std::sync::mpsc;
+use std::thread;
 use tracing::instrument;
-use tracing::{debug, warn};
+use tracing::span;
-
+use tracing::{debug, error, info, warn, Level};
-use anyhow::Result;
-use linux_embedded_hal::gpio_cdev::{Chip, LineRequestFlags};
-
-use crate::dither::DitheredImage;
 
 pub trait EInkPanel {
     fn display(&mut self, buf: &DitheredImage) -> Result<()>;
@@ -88,3 +90,34 @@ impl EInkPanel for FakeEInk {
         Ok(())
     }
 }
+
+/// Create a thread that can take dithered images and display them. This allows the display to be
+/// used in an async context since updating the display can take ~30 seconds.
+#[must_use]
+pub fn create_display_thread(
+    mut display: Box<dyn EInkPanel + Send>,
+) -> (thread::JoinHandle<()>, mpsc::Sender<Box<DitheredImage>>) {
+    let (tx, rx) = mpsc::channel::<Box<DitheredImage>>();
+    let handle = thread::spawn(move || {
+        let span = span!(Level::INFO, "display_thread");
+        let _enter = span.enter();
+        loop {
+            let res = rx.recv();
+            match res {
+                Ok(img) => {
+                    info!("Received an image to display");
+                    if let Err(e) = display.display(&img) {
+                        error!("Error displaying image: {e}");
+                        return;
+                    }
+                    info!("Successfully set display image");
+                }
+                Err(e) => {
+                    error!("Error reading image from channel: {e}");
+                    return;
+                }
+            }
+        }
+    });
+    (handle, tx)
+}