在通过通道传递消息时，我试图对接收到的响应进行调试，但不幸的是，我的窗口冻结，当试图打印调试时，table对象的列表无限打印。
我试图挽救局面的努力已被证明是徒劳的。
之后的sql查询的目标是加载表的列表及其关系，我已经将其分配给Diagram.tables并传递消息通道
在尝试接收通道self.handle_responses();并尝试通过时雄运行时执行查询函数之后，
我终于把表的列表翻了一遍
并将该列表添加到可以呈现的方形向量。
不幸的是，表的列表不停地循环，甚至挂起了Windows。
我以为表向量会重复一次，我可以利用它，但不成功。
这是从eframe template修改而来的完整代码app.rs

use std::sync::mpsc::{self, Receiver, Sender};

use crate::meta::{get_metadata, Table};
use egui::{Color32, FontId, Sense, Vec2};
use emath::{Align2, Pos2};
use std::fmt;
use tokio::runtime;
use tokio_postgres::NoTls;

pub const INIT_POS: Pos2 = egui::pos2(10.0, 15.0);
pub const ATTR_SIZE: Vec2 = egui::vec2(150.0, 25.0);

pub enum TaskMessage {
    //Applicaple to any scenario, behaves almost like a callback
    Generic(Box<dyn FnOnce(&mut Diagram) + Send>),
}


#[derive(serde::Deserialize, serde::Serialize)]
#[serde(default = "Diagram::new")]
pub struct Diagram {
    pub shapes: Vec<Square>,
    pub tables: Vec<Table>,
    canvas_size: Vec2,
    #[serde(skip)]
    task_reciever: Receiver<TaskMessage>,
spawing them

    #[serde(skip)]
    _task_sender: Sender<TaskMessage>,
}

impl Diagram {
    fn new() -> Self {
        let (_task_sender, task_reciever) = mpsc::channel::<TaskMessage>();
        Self {
            shapes: vec![],
            tables: vec![],
            canvas_size: Vec2::splat(400.0),
            task_reciever,
            _task_sender,
        }
    }

    pub fn handle_responses(&mut self) {
        while let Ok(response) = self.task_reciever.try_recv() {
            match response {
                TaskMessage::Generic(gen_function) => {
                    gen_function(self);
                }
            }
        }
    }

}

impl egui::Widget for &mut Diagram {
    fn ui(self, ui: &mut egui::Ui) -> egui::Response {
        egui::Frame::canvas(ui.style())
            .show(ui, |ui| {
                egui::ScrollArea::new([true; 2]).show(ui, |ui| {
                    let sender = self._task_sender.clone();
                    let other_ctx = ui.ctx().clone();

                    self.handle_responses();
                    tokio::task::spawn(async {
                        let schema = "public".to_string();

                        get_metadata(schema, other_ctx, sender).await
                    });

                    eprintln!("{:#?}", self.tables);
                    for table in &self.tables {
                        if let Some(table_name) =
                            table.table.get("table_name").and_then(|v| v.as_str())
                        {
                            // println!("{:#?}", table_name);
                            let square = Square::new(table_name.to_string());
                            self.shapes.push(square);
                        }
                    }

                    for shape in self.shapes.iter_mut() {
                        shape.render(ui);
                    }
                    ui.allocate_at_least(self.canvas_size, Sense::hover());
                });
                // ui.ctx().set_debug_on_hover(true);
            })
            .response
    }
}

#[derive(serde::Deserialize, serde::Serialize, Debug)]
pub struct Square {
    position: egui::Pos2,
    dimension: egui::Vec2,
    label: String,
}

impl Square {
    fn new(label: String) -> Self {
        Self {
            position: egui::pos2(INIT_POS.x, INIT_POS.y),
            dimension: egui::vec2(ATTR_SIZE.x, ATTR_SIZE.y),
            attributes: vec![InnerSquare::new()],
            label,
        }
    }
    fn render(&mut self, ui: &mut egui::Ui) {
        let square_body = egui::Rect::from_min_size(self.position, self.dimension);
        //"finalized rect" which is offset properly
        let transformed_rect = {
            let resp = ui.allocate_rect(ui.available_rect_before_wrap(), egui::Sense::click());
            let relative_to_screen = egui::emath::RectTransform::from_to(
                egui::Rect::from_min_size(Pos2::ZERO, resp.rect.size()),
                resp.rect,
            );
            relative_to_screen.transform_rect(square_body)
        };

        let frame = {
            let rounding_radius = 2.0;
            let fill = egui::Color32::LIGHT_GREEN;
            let stroke = egui::epaint::Stroke::new(2.0, Color32::DARK_BLUE);
            egui::Frame::none()
                .rounding(rounding_radius)
                .fill(fill)
                .stroke(stroke)
                .inner_margin(10.0)
        };
        //Creates a new ui where our square is supposed to appear
        ui.allocate_ui_at_rect(transformed_rect, |ui| {
            frame.show(ui, |ui| {
                //draw each attribute
                ui.label(
                    egui::RichText::new(&self.label)
                        .heading()
                        .color(egui::Color32::BLACK),
                );
                for inner_square in self.attributes.iter_mut() {
                    inner_square.render(ui);
                }
            });
        });
    }
}

#[derive(serde::Deserialize, serde::Serialize)]
#[serde(default)] // if we add new fields, give them default values when deserializing old state
pub struct TemplateApp {
    diagram: Diagram,
    label: String,
    #[serde(skip)]
    value: f32,
    //this is what the ui thread will just to catch returns of tasks, in this case it's the std
    //mpsc channels, but any channel which has smiliar behaviour works
}

impl Default for TemplateApp {
    fn default() -> Self {
        Self {
            // Example stuff:
            label: "Hello World!".to_owned(),
            value: 2.7,
            diagram: Diagram::new(),
        }
    }
}

impl TemplateApp {
    /// Called once before the first frame.
    pub fn new(cc: &eframe::CreationContext<'_>) -> Self {
        Default::default()
    }
}

impl eframe::App for TemplateApp {
    /// Called by the frame work to save state before shutdown.
    fn save(&mut self, storage: &mut dyn eframe::Storage) {
        eframe::set_value(storage, eframe::APP_KEY, self);
    }

    /// Called each time the UI needs repainting, which may be many times per second.
    /// Put your widgets into a `SidePanel`, `TopPanel`, `CentralPanel`, `Window` or `Area`.
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        let Self {
            label,
            diagram,
            value,
        } = self;

        // #[cfg(not(target_arch = "wasm32"))] // no File->Quit on web pages!
        egui::TopBottomPanel::top("top_panel").show(ctx, |ui| {
            // The top panel is often a good place for a menu bar:
            egui::menu::bar(ui, |ui| {
                ui.menu_button("File", |ui| {
                    if ui.button("Quit").clicked() {
                        _frame.close();
                    }
                });
            });
        });

        egui::CentralPanel::default().show(ctx, |ui| {
            ui.add(&mut self.diagram) // The central panel the region left after adding TopPanel's and SidePanel's
        });

        if false {
            egui::Window::new("Window").show(ctx, |ui| {
                ui.label("Panel Area");
            });
        }
    }
}

以及负责从tokio-postgre查询数据库的代码
//meta.rs

use serde::{Deserialize, Serialize};
use serde_json::Value;
use std::error::Error;
use std::fmt;
use std::ptr::null;
use std::sync::mpsc::Sender;
use std::{thread, time};
use tokio::runtime::Runtime;
use tokio_postgres::tls::NoTlsStream;
use tokio_postgres::{Client, Connection, Error as TokioError, NoTls, Row, Socket};

// Define a custom error enum
#[derive(Debug)]
pub enum MetadataError {
    JsonResponseNotFound,
    RowNotFound,
    // PostgresError(PostgresError),
    TokioError(TokioError),
}

impl fmt::Display for MetadataError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            MetadataError::JsonResponseNotFound => write!(f, "No JSON response found"),
            MetadataError::RowNotFound => write!(f, "No row found in the result"),
            // MetadataError::PostgresError(ref err) => err.fmt(f),
            MetadataError::TokioError(ref err) => err.fmt(f),
        }
    }
}

impl From<tokio_postgres::Error> for MetadataError {
    fn from(error: tokio_postgres::Error) -> MetadataError {
        MetadataError::TokioError(error)
    }
}

impl Error for MetadataError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match *self {
            MetadataError::JsonResponseNotFound | MetadataError::RowNotFound => None,
            // MetadataError::PostgresError(ref err) => Some(err),
            MetadataError::TokioError(ref err) => Some(err),
        }
    }
}

#[derive(Debug, Serialize, Deserialize)]
pub struct Table {
    pub table: serde_json::Value,
}

impl From<Row> for Table {
    fn from(row: Row) -> Self {
        Self { table: row.get(0) }
    }
}

pub async fn get_metadata(
    schema: String,
    ctx: egui::Context,
    sender: Sender<crate::app::TaskMessage>,
) -> Result<(), MetadataError> {
    let qry = r#"
        select row_to_json(Tb) 
    --- table listing query
    "#;
    let (client, connection) = tokio_postgres::connect(
        "postgresql://postgres:chou1979@localhost/authenticate",
        NoTls,
    )
    .await
    .unwrap();
    // The connection object performs the actual communication with the database,
    // so spawn it off to run on its own.
    let conn = tokio::spawn(async move {
        if let Err(e) = connection.await {
            eprintln!("connection error: {}", e);
        }
    });

    let stmt = client.prepare(qry).await?;
    let rows = client.query(&stmt, &[&schema]).await?;

    let finalized: Vec<Table> = rows.into_iter().map(Table::from).collect();
    conn.abort();
    // println!("{:#?}", finalized);

    let gen_function = move |diagram: &mut crate::app::Diagram| {
        diagram.tables = finalized
    };
    // sender.send(Box::new(gen_function)).unwrap();
    sender
        .send(crate::app::TaskMessage::Generic(Box::new(gen_function)))
        .unwrap();
    ctx.request_repaint();

    Ok(())
}