demo: Proof-of-concept, dual-thread designtopic/design-poc

3 files changed, 180 insertions, 0 deletions

diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+/Cargo.lock
+/target
diff --git a/Cargo.toml b/Cargo.toml
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+++ b/Cargo.toml
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+[package]
+name = "ccc"
+version = "0.0.1"
+edition = "2021"
+
+[dependencies]
+crossbeam-channel = "0.5.13"
+cursive = "0.20.0"
diff --git a/src/main.rs b/src/main.rs
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+++ b/src/main.rs
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+use {
+    crossbeam_channel::{
+        Receiver,
+        Sender,
+
+        unbounded,
+    },
+    cursive::{
+        Cursive,
+        CursiveExt,
+        Printer,
+        Rect,
+        View,
+        XY,
+
+        direction::Direction,
+        event::{
+            Event,
+            EventResult,
+        },
+        view::{
+            CannotFocus,
+            Nameable,
+            Selector,
+            ViewNotFound,
+        },
+        views::{
+            Button,
+            LinearLayout,
+            TextView,
+        }
+    },
+    std::{
+        time::Duration,
+        thread::{
+            self,
+            sleep,
+        },
+    }
+};
+
+type CursiveSender = Sender<Box<(dyn for<'a> FnOnce(&'a mut Cursive) + Send + 'static)>>;
+
+struct DataView {
+    data: Option<String>,
+    view: TextView,
+}
+
+impl DataView {
+    pub fn new() -> Self {
+        Self {
+            data: None,
+            view: TextView::new("uninitialized"),
+        }
+    }
+
+    fn set_data(&mut self, data: &str) {
+        self.data = Some(data.to_owned());
+        self.view.set_content(data.to_string())
+    }
+}
+
+impl View for DataView {
+    fn draw(&self, printer: &Printer<'_, '_>) {
+        self.view.draw(printer)
+    }
+
+    fn layout(&mut self, xy: XY<usize>) {
+        self.view.layout(xy)
+    }
+
+    fn needs_relayout(&self) -> bool {
+        self.view.needs_relayout()
+    }
+
+    fn required_size(&mut self, constraint: XY<usize>) -> XY<usize> {
+        self.view.required_size(constraint)
+    }
+
+    fn on_event(&mut self, event: Event) -> EventResult {
+        self.view.on_event(event)
+    }
+
+    // fn call_on_any(), should not be needed for this view.
+
+    fn focus_view(&mut self, selector: &Selector<'_>) -> Result<EventResult, ViewNotFound> {
+        self.view.focus_view(selector)
+    }
+
+    fn take_focus( &mut self, source: Direction) -> Result<EventResult, CannotFocus> {
+        self.view.take_focus(source)
+    }
+
+    fn important_area(&self, view_size: XY<usize>) -> Rect {
+        self.view.important_area(view_size)
+    }
+
+    fn type_name(&self) -> &'static str {
+        "DataView"
+    }
+}
+
+fn data_request(cur: &mut Cursive) {
+    if let Some(sender) = cur.user_data::<Sender<bool>>() {
+        let _ = sender.send(true);
+    }
+}
+
+fn populate_data(s: &mut Cursive, is_data: bool) {
+    if let Some(mut data_view) = s.find_name::<DataView>("populate_me") {
+        if is_data {
+            data_view.set_data("populated")
+        } else {
+            data_view.set_data("initialized")
+        }
+    }
+}
+
+fn background_thread(reciever: Receiver<bool>, sender: CursiveSender) {
+    while let Ok(msg) = reciever.recv() {
+        eprintln!("Received a message. Sleeping 3 seconds before sending response.");
+        sleep(Duration::from_secs(3));
+        let _ = sender.send(Box::new(move |s| populate_data(s, msg)));
+    }
+}
+
+fn main() {
+    // In order to maintain the main thread responsive in dealing with the user interface, we wish
+    // to offload all server communication to a background thread. This code demonstrates how to
+    // send a message from the ui, process it in the background and send the result back for the
+    // user interface to update the content of its view.
+
+    // Firstly, we need a channel pair for sending a message from the ui to the worker thread.
+    let (wrk_sender, wrk_receiver) = unbounded::<bool>();
+
+    // We then construct the actual user interface. Our DataView, a button to trigger populating
+    // it and a button to quit the app.
+    let mut app = Cursive::new();
+    let mut horizontal = LinearLayout::horizontal();
+    let mut vertical = LinearLayout::vertical();
+    let data_view = DataView::new().with_name("populate_me");
+    let populate_button = Button::new("data", data_request);
+    let quit_button = Button::new("quit", |s| s.quit());
+    vertical.add_child(data_view);
+    horizontal.add_child(populate_button);
+    horizontal.add_child(quit_button);
+    vertical.add_child(horizontal);
+    app.add_layer(vertical);
+
+    // Once having created the app, we send a request to initialize our view.
+    let _ = wrk_sender.send(false);
+
+    // We then place the sender in the user_data, to make it available for any ui function.
+    app.set_user_data(wrk_sender);
+
+    // Getting the callback sender from the user interface, needed for the worker to respond.
+    let ui_sender = app.cb_sink().clone();
+
+    // Then we launch the background worker thread, providing it the appropriate channel ends.
+    let _worker = thread::spawn(move || background_thread(wrk_receiver, ui_sender));
+
+    // Lastly we launch the user interface.
+    app.run();
+
+    // Three seconds after launching, the text changes from "uninitialized" to "initialized" and
+    // further, three seconds after pressing the <data> button the text becomes "populated".
+    //
+    // Essentially, this design should work for the complete program. Yet with some slightly more
+    // expressive choice of datatypes than merely a bool.
+}