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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
use deno_core::anyhow::Error;use deno_core::op;use deno_core::Extension;use deno_core::JsRuntime;use deno_core::OpState;use deno_core::RuntimeOptions;use futures::channel::mpsc;use futures::stream::StreamExt;use std::task::Poll;
// This is a hack to make the `#[op]` macro work with// deno_core examples.// You can remove this:use deno_core::*;
type Task = Box<dyn FnOnce()>;
fn main() {  let my_ext = Extension::builder()    .ops(vec![op_schedule_task::decl()])    .event_loop_middleware(|state, cx| {      let recv = state.borrow_mut::<mpsc::UnboundedReceiver<Task>>();      let mut ref_loop = false;      while let Poll::Ready(Some(call)) = recv.poll_next_unpin(cx) {        call();        ref_loop = true; // `call` can callback into runtime and schedule new callbacks :-)      }      ref_loop    })    .state(move |state| {      let (tx, rx) = mpsc::unbounded::<Task>();      state.put(tx);      state.put(rx);
      Ok(())    })    .build();
  // Initialize a runtime instance  let mut js_runtime = JsRuntime::new(RuntimeOptions {    extensions: vec![my_ext],    ..Default::default()  });  let runtime = tokio::runtime::Builder::new_current_thread()    .enable_all()    .build()    .unwrap();
  let future = async move {    // Schedule 10 tasks.    js_runtime    .execute_script(      "<usage>",       r#"for (let i = 1; i <= 10; i++) Deno.core.opSync("op_schedule_task", i);"#    )    .unwrap();    js_runtime.run_event_loop(false).await  };  runtime.block_on(future).unwrap();}
#[op]fn op_schedule_task(state: &mut OpState, i: u8) -> Result<(), Error> {  let tx = state.borrow_mut::<mpsc::UnboundedSender<Task>>();  tx.unbounded_send(Box::new(move || println!("Hello, world! x{}", i)))    .expect("unbounded_send failed");  Ok(())}