implement Worker.terminate() and self.close() (#4684)

12 files changed, 370 insertions, 102 deletions

diff --git a/cli/compilers/ts.rs b/cli/compilers/ts.rs
index 641f16bca..c78d7ef57 100644
--- a/cli/compilers/ts.rs
+++ b/cli/compilers/ts.rs
@@ -16,8 +16,8 @@ use crate::startup_data;
 use crate::state::*;
 use crate::tokio_util;
 use crate::version;
+use crate::web_worker::WebWorkerHandle;
 use crate::worker::WorkerEvent;
-use crate::worker::WorkerHandle;
 use deno_core::Buf;
 use deno_core::ErrBox;
 use deno_core::ModuleSpecifier;
@@ -609,7 +609,7 @@ async fn execute_in_thread(
   req: Buf,
 ) -> Result<Buf, ErrBox> {
   let (handle_sender, handle_receiver) =
-    std::sync::mpsc::sync_channel::<Result<WorkerHandle, ErrBox>>(1);
+    std::sync::mpsc::sync_channel::<Result<WebWorkerHandle, ErrBox>>(1);
   let builder =
     std::thread::Builder::new().name("deno-ts-compiler".to_string());
   let join_handle = builder.spawn(move || {
@@ -618,15 +618,16 @@ async fn execute_in_thread(
     drop(handle_sender);
     tokio_util::run_basic(worker).expect("Panic in event loop");
   })?;
-  let mut handle = handle_receiver.recv().unwrap()?;
-  handle.post_message(req).await?;
+  let handle = handle_receiver.recv().unwrap()?;
+  handle.post_message(req)?;
   let event = handle.get_event().await.expect("Compiler didn't respond");
   let buf = match event {
     WorkerEvent::Message(buf) => Ok(buf),
     WorkerEvent::Error(error) => Err(error),
+    WorkerEvent::TerminalError(error) => Err(error),
   }?;
   // Shutdown worker and wait for thread to finish
-  handle.sender.close_channel();
+  handle.terminate();
   join_handle.join().unwrap();
   Ok(buf)
 }
diff --git a/cli/compilers/wasm.rs b/cli/compilers/wasm.rs
index d81138482..4e8ba78f3 100644
--- a/cli/compilers/wasm.rs
+++ b/cli/compilers/wasm.rs
@@ -6,8 +6,8 @@ use crate::global_state::GlobalState;
 use crate::startup_data;
 use crate::state::*;
 use crate::tokio_util;
+use crate::web_worker::WebWorkerHandle;
 use crate::worker::WorkerEvent;
-use crate::worker::WorkerHandle;
 use deno_core::Buf;
 use deno_core::ErrBox;
 use deno_core::ModuleSpecifier;
@@ -118,7 +118,7 @@ async fn execute_in_thread(
   req: Buf,
 ) -> Result<Buf, ErrBox> {
   let (handle_sender, handle_receiver) =
-    std::sync::mpsc::sync_channel::<Result<WorkerHandle, ErrBox>>(1);
+    std::sync::mpsc::sync_channel::<Result<WebWorkerHandle, ErrBox>>(1);
   let builder =
     std::thread::Builder::new().name("deno-wasm-compiler".to_string());
   let join_handle = builder.spawn(move || {
@@ -127,15 +127,16 @@ async fn execute_in_thread(
     drop(handle_sender);
     tokio_util::run_basic(worker).expect("Panic in event loop");
   })?;
-  let mut handle = handle_receiver.recv().unwrap()?;
-  handle.post_message(req).await?;
+  let handle = handle_receiver.recv().unwrap()?;
+  handle.post_message(req)?;
   let event = handle.get_event().await.expect("Compiler didn't respond");
   let buf = match event {
     WorkerEvent::Message(buf) => Ok(buf),
     WorkerEvent::Error(error) => Err(error),
+    WorkerEvent::TerminalError(error) => Err(error),
   }?;
   // Shutdown worker and wait for thread to finish
-  handle.sender.close_channel();
+  handle.terminate();
   join_handle.join().unwrap();
   Ok(buf)
 }
diff --git a/cli/js/web/workers.ts b/cli/js/web/workers.ts
index a62ca0b77..7a0abbbdb 100644
--- a/cli/js/web/workers.ts
+++ b/cli/js/web/workers.ts
@@ -127,6 +127,14 @@ export class WorkerImpl extends EventTarget implements Worker {
 
       const type = event.type;
 
+      if (type === "terminalError") {
+        this.#terminated = true;
+        if (!this.#handleError(event.error)) {
+          throw Error(event.error.message);
+        }
+        continue;
+      }
+
       if (type === "msg") {
         if (this.onmessage) {
           const message = decodeMessage(new Uint8Array(event.data));
diff --git a/cli/ops/web_worker.rs b/cli/ops/web_worker.rs
index dd7b6e34a..8cade7d40 100644
--- a/cli/ops/web_worker.rs
+++ b/cli/ops/web_worker.rs
@@ -3,10 +3,10 @@ use super::dispatch_json::{JsonOp, Value};
 use crate::op_error::OpError;
 use crate::ops::json_op;
 use crate::state::State;
+use crate::web_worker::WebWorkerHandle;
 use crate::worker::WorkerEvent;
 use deno_core::*;
 use futures::channel::mpsc;
-use futures::sink::SinkExt;
 use std::convert::From;
 
 pub fn web_worker_op<D>(
@@ -25,7 +25,32 @@ where
         -> Result<JsonOp, OpError> { dispatcher(&sender, args, zero_copy) }
 }
 
-pub fn init(i: &mut Isolate, s: &State, sender: &mpsc::Sender<WorkerEvent>) {
+pub fn web_worker_op2<D>(
+  handle: WebWorkerHandle,
+  sender: mpsc::Sender<WorkerEvent>,
+  dispatcher: D,
+) -> impl Fn(Value, Option<ZeroCopyBuf>) -> Result<JsonOp, OpError>
+where
+  D: Fn(
+    WebWorkerHandle,
+    &mpsc::Sender<WorkerEvent>,
+    Value,
+    Option<ZeroCopyBuf>,
+  ) -> Result<JsonOp, OpError>,
+{
+  move |args: Value,
+        zero_copy: Option<ZeroCopyBuf>|
+        -> Result<JsonOp, OpError> {
+    dispatcher(handle.clone(), &sender, args, zero_copy)
+  }
+}
+
+pub fn init(
+  i: &mut Isolate,
+  s: &State,
+  sender: &mpsc::Sender<WorkerEvent>,
+  handle: WebWorkerHandle,
+) {
   i.register_op(
     "op_worker_post_message",
     s.core_op(json_op(web_worker_op(
@@ -35,7 +60,11 @@ pub fn init(i: &mut Isolate, s: &State, sender: &mpsc::Sender<WorkerEvent>) {
   );
   i.register_op(
     "op_worker_close",
-    s.core_op(json_op(web_worker_op(sender.clone(), op_worker_close))),
+    s.core_op(json_op(web_worker_op2(
+      handle,
+      sender.clone(),
+      op_worker_close,
+    ))),
   );
 }
 
@@ -47,18 +76,23 @@ fn op_worker_post_message(
 ) -> Result<JsonOp, OpError> {
   let d = Vec::from(data.unwrap().as_ref()).into_boxed_slice();
   let mut sender = sender.clone();
-  let fut = sender.send(WorkerEvent::Message(d));
-  futures::executor::block_on(fut).expect("Failed to post message to host");
+  sender
+    .try_send(WorkerEvent::Message(d))
+    .expect("Failed to post message to host");
   Ok(JsonOp::Sync(json!({})))
 }
 
 /// Notify host that guest worker closes
 fn op_worker_close(
+  handle: WebWorkerHandle,
   sender: &mpsc::Sender<WorkerEvent>,
   _args: Value,
   _data: Option<ZeroCopyBuf>,
 ) -> Result<JsonOp, OpError> {
   let mut sender = sender.clone();
+  // Notify parent that we're finished
   sender.close_channel();
+  // Terminate execution of current worker
+  handle.terminate();
   Ok(JsonOp::Sync(json!({})))
 }
diff --git a/cli/ops/worker_host.rs b/cli/ops/worker_host.rs
index ee448eb83..a04250099 100644
--- a/cli/ops/worker_host.rs
+++ b/cli/ops/worker_host.rs
@@ -1,7 +1,6 @@
 // Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
 use super::dispatch_json::{Deserialize, JsonOp, Value};
 use crate::fmt_errors::JSError;
-use crate::futures::SinkExt;
 use crate::global_state::GlobalState;
 use crate::op_error::OpError;
 use crate::permissions::DenoPermissions;
@@ -9,11 +8,10 @@ use crate::startup_data;
 use crate::state::State;
 use crate::tokio_util::create_basic_runtime;
 use crate::web_worker::WebWorker;
+use crate::web_worker::WebWorkerHandle;
 use crate::worker::WorkerEvent;
-use crate::worker::WorkerHandle;
 use deno_core::*;
 use futures::future::FutureExt;
-use futures::future::TryFutureExt;
 use std::convert::From;
 use std::thread::JoinHandle;
 
@@ -58,9 +56,9 @@ fn run_worker_thread(
   specifier: ModuleSpecifier,
   has_source_code: bool,
   source_code: String,
-) -> Result<(JoinHandle<()>, WorkerHandle), ErrBox> {
+) -> Result<(JoinHandle<()>, WebWorkerHandle), ErrBox> {
   let (handle_sender, handle_receiver) =
-    std::sync::mpsc::sync_channel::<Result<WorkerHandle, ErrBox>>(1);
+    std::sync::mpsc::sync_channel::<Result<WebWorkerHandle, ErrBox>>(1);
 
   let builder =
     std::thread::Builder::new().name(format!("deno-worker-{}", name));
@@ -78,6 +76,7 @@ fn run_worker_thread(
     }
 
     let mut worker = result.unwrap();
+    let name = worker.name.to_string();
     // Send thread safe handle to newly created worker to host thread
     handle_sender.send(Ok(worker.thread_safe_handle())).unwrap();
     drop(handle_sender);
@@ -109,7 +108,8 @@ fn run_worker_thread(
 
     if let Err(e) = result {
       let mut sender = worker.internal_channels.sender.clone();
-      futures::executor::block_on(sender.send(WorkerEvent::Error(e)))
+      sender
+        .try_send(WorkerEvent::TerminalError(e))
         .expect("Failed to post message to host");
 
       // Failure to execute script is a terminal error, bye, bye.
@@ -120,6 +120,7 @@ fn run_worker_thread(
     // that means that we should store JoinHandle to thread to ensure
     // that it actually terminates.
     rt.block_on(worker).expect("Panic in event loop");
+    debug!("Worker thread shuts down {}", &name);
   })?;
 
   let worker_handle = handle_receiver.recv().unwrap()?;
@@ -205,6 +206,28 @@ fn op_host_terminate_worker(
 fn serialize_worker_event(event: WorkerEvent) -> Value {
   match event {
     WorkerEvent::Message(buf) => json!({ "type": "msg", "data": buf }),
+    WorkerEvent::TerminalError(error) => {
+      let mut serialized_error = json!({
+        "type": "terminalError",
+        "error": {
+          "message": error.to_string(),
+        }
+      });
+
+      if let Ok(js_error) = error.downcast::<JSError>() {
+        serialized_error = json!({
+          "type": "terminalError",
+          "error": {
+            "message": js_error.message,
+            "fileName": js_error.script_resource_name,
+            "lineNumber": js_error.line_number,
+            "columnNumber": js_error.start_column,
+          }
+        });
+      }
+
+      serialized_error
+    }
     WorkerEvent::Error(error) => {
       let mut serialized_error = json!({
         "type": "error",
@@ -247,13 +270,30 @@ fn op_host_get_message(
   let state_ = state.clone();
   let op = async move {
     let response = match worker_handle.get_event().await {
-      Some(event) => serialize_worker_event(event),
+      Some(event) => {
+        // Terminal error means that worker should be removed from worker table.
+        if let WorkerEvent::TerminalError(_) = &event {
+          let mut state_ = state_.borrow_mut();
+          if let Some((join_handle, mut worker_handle)) =
+            state_.workers.remove(&id)
+          {
+            worker_handle.sender.close_channel();
+            join_handle.join().expect("Worker thread panicked");
+          }
+        }
+        serialize_worker_event(event)
+      }
       None => {
+        // Worker shuts down
         let mut state_ = state_.borrow_mut();
-        let (join_handle, mut worker_handle) =
-          state_.workers.remove(&id).expect("No worker handle found");
-        worker_handle.sender.close_channel();
-        join_handle.join().expect("Worker thread panicked");
+        // Try to remove worker from workers table - NOTE: `Worker.terminate()` might have been called
+        // already meaning that we won't find worker in table - in that case ignore.
+        if let Some((join_handle, mut worker_handle)) =
+          state_.workers.remove(&id)
+        {
+          worker_handle.sender.close_channel();
+          join_handle.join().expect("Worker thread panicked");
+        }
         json!({ "type": "close" })
       }
     };
@@ -276,9 +316,8 @@ fn op_host_post_message(
   let state = state.borrow();
   let (_, worker_handle) =
     state.workers.get(&id).expect("No worker handle found");
-  let fut = worker_handle
+  worker_handle
     .post_message(msg)
-    .map_err(|e| OpError::other(e.to_string()));
-  futures::executor::block_on(fut)?;
+    .map_err(|e| OpError::other(e.to_string()))?;
   Ok(JsonOp::Sync(json!({})))
 }
diff --git a/cli/state.rs b/cli/state.rs
index d55e4e5eb..228ef1200 100644
--- a/cli/state.rs
+++ b/cli/state.rs
@@ -8,7 +8,7 @@ use crate::op_error::OpError;
 use crate::ops::JsonOp;
 use crate::ops::MinimalOp;
 use crate::permissions::DenoPermissions;
-use crate::worker::WorkerHandle;
+use crate::web_worker::WebWorkerHandle;
 use deno_core::Buf;
 use deno_core::CoreOp;
 use deno_core::ErrBox;
@@ -62,7 +62,7 @@ pub struct StateInner {
   pub import_map: Option<ImportMap>,
   pub metrics: Metrics,
   pub global_timer: GlobalTimer,
-  pub workers: HashMap<u32, (JoinHandle<()>, WorkerHandle)>,
+  pub workers: HashMap<u32, (JoinHandle<()>, WebWorkerHandle)>,
   pub next_worker_id: u32,
   pub start_time: Instant,
   pub seeded_rng: Option<StdRng>,
diff --git a/cli/tests/subdir/busy_worker.js b/cli/tests/subdir/busy_worker.js
new file mode 100644
index 000000000..7deba0321
--- /dev/null
+++ b/cli/tests/subdir/busy_worker.js
@@ -0,0 +1,8 @@
+self.onmessage = function (_evt) {
+  // infinite loop
+  for (let i = 0; true; i++) {
+    if (i % 1000 == 0) {
+      postMessage(i);
+    }
+  }
+};
diff --git a/cli/tests/subdir/racy_worker.js b/cli/tests/subdir/racy_worker.js
new file mode 100644
index 000000000..83756b791
--- /dev/null
+++ b/cli/tests/subdir/racy_worker.js
@@ -0,0 +1,21 @@
+// See issue for details
+// https://github.com/denoland/deno/issues/4080
+//
+// After first call to `postMessage() this worker schedules
+// [close(), postMessage()] ops on the same turn of microtask queue
+// (because message is rather big).
+// Only single `postMessage()` call should make it
+// to host, ie. after calling `close()` no more code should be run.
+
+setTimeout(() => {
+  close();
+}, 50);
+
+while (true) {
+  await new Promise((done) => {
+    setTimeout(() => {
+      postMessage({ buf: new Array(999999) });
+      done();
+    });
+  });
+}
diff --git a/cli/tests/workers_test.out b/cli/tests/workers_test.out
index efc0ce57c..ca7500917 100644
--- a/cli/tests/workers_test.out
+++ b/cli/tests/workers_test.out
@@ -1,7 +1,9 @@
-running 4 tests
-test workersBasic ... ok [WILDCARD]
-test nestedWorker ... ok [WILDCARD]
-test workerThrowsWhenExecuting ... ok [WILDCARD]
-test workerCanUseFetch ... ok [WILDCARD]
+running 6 tests
+test worker terminate ... ok [WILDCARD]
+test worker nested ... ok [WILDCARD]
+test worker throws when executing ... ok [WILDCARD]
+test worker fetch API ... ok [WILDCARD]
+test worker terminate busy loop ... ok [WILDCARD]
+test worker race condition ... ok [WILDCARD]
 
-test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out [WILDCARD]
+test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out [WILDCARD]
diff --git a/cli/tests/workers_test.ts b/cli/tests/workers_test.ts
index 42bd96d96..2c56a491c 100644
--- a/cli/tests/workers_test.ts
+++ b/cli/tests/workers_test.ts
@@ -28,11 +28,10 @@ export function createResolvable<T>(): Resolvable<T> {
 }
 
 Deno.test({
-  name: "workersBasic",
-  // FIXME(bartlomieju):
-  disableOpSanitizer: true,
+  name: "worker terminate",
   fn: async function (): Promise<void> {
     const promise = createResolvable();
+
     const jsWorker = new Worker("../tests/subdir/test_worker.js", {
       type: "module",
       name: "jsWorker",
@@ -59,13 +58,13 @@ Deno.test({
 
     jsWorker.postMessage("Hello World");
     await promise;
+    tsWorker.terminate();
+    jsWorker.terminate();
   },
 });
 
 Deno.test({
-  name: "nestedWorker",
-  // FIXME(bartlomieju):
-  disableOpSanitizer: true,
+  name: "worker nested",
   fn: async function (): Promise<void> {
     const promise = createResolvable();
 
@@ -81,13 +80,12 @@ Deno.test({
 
     nestedWorker.postMessage("Hello World");
     await promise;
+    nestedWorker.terminate();
   },
 });
 
 Deno.test({
-  name: "workerThrowsWhenExecuting",
-  // FIXME(bartlomieju):
-  disableOpSanitizer: true,
+  name: "worker throws when executing",
   fn: async function (): Promise<void> {
     const promise = createResolvable();
     const throwingWorker = new Worker("../tests/subdir/throwing_worker.js", {
@@ -102,13 +100,12 @@ Deno.test({
     };
 
     await promise;
+    throwingWorker.terminate();
   },
 });
 
 Deno.test({
-  name: "workerCanUseFetch",
-  // FIXME(bartlomieju):
-  disableOpSanitizer: true,
+  name: "worker fetch API",
   fn: async function (): Promise<void> {
     const promise = createResolvable();
 
@@ -129,5 +126,61 @@ Deno.test({
     };
 
     await promise;
+    fetchingWorker.terminate();
+  },
+});
+
+Deno.test({
+  name: "worker terminate busy loop",
+  fn: async function (): Promise<void> {
+    const promise = createResolvable();
+
+    const busyWorker = new Worker("../tests/subdir/busy_worker.js", {
+      type: "module",
+    });
+
+    let testResult = 0;
+
+    busyWorker.onmessage = (e): void => {
+      testResult = e.data;
+      if (testResult >= 10000) {
+        busyWorker.terminate();
+        busyWorker.onmessage = (_e): void => {
+          throw new Error("unreachable");
+        };
+        setTimeout(() => {
+          assertEquals(testResult, 10000);
+          promise.resolve();
+        }, 100);
+      }
+    };
+
+    busyWorker.postMessage("ping");
+    await promise;
+  },
+});
+
+Deno.test({
+  name: "worker race condition",
+  fn: async function (): Promise<void> {
+    // See issue for details
+    // https://github.com/denoland/deno/issues/4080
+    const promise = createResolvable();
+
+    const racyWorker = new Worker("../tests/subdir/racy_worker.js", {
+      type: "module",
+    });
+
+    racyWorker.onmessage = (e): void => {
+      assertEquals(e.data.buf.length, 999999);
+      racyWorker.onmessage = (_e): void => {
+        throw new Error("unreachable");
+      };
+      setTimeout(() => {
+        promise.resolve();
+      }, 100);
+    };
+
+    await promise;
   },
 });
diff --git a/cli/web_worker.rs b/cli/web_worker.rs
index 683ba9ef4..795409175 100644
--- a/cli/web_worker.rs
+++ b/cli/web_worker.rs
@@ -3,17 +3,68 @@ use crate::ops;
 use crate::state::State;
 use crate::worker::Worker;
 use crate::worker::WorkerEvent;
+use crate::worker::WorkerHandle;
+use deno_core::v8;
 use deno_core::ErrBox;
 use deno_core::StartupData;
+use futures::channel::mpsc;
 use futures::future::FutureExt;
 use futures::stream::StreamExt;
-use futures::SinkExt;
 use std::future::Future;
 use std::ops::Deref;
 use std::ops::DerefMut;
 use std::pin::Pin;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
 use std::task::Context;
 use std::task::Poll;
+
+/// Wrapper for `WorkerHandle` that adds functionality
+/// for terminating workers.
+///
+/// This struct is used by host as well as worker itself.
+///
+/// Host uses it to communicate with worker and terminate it,
+/// while worker uses it only to finish execution on `self.close()`.
+#[derive(Clone)]
+pub struct WebWorkerHandle {
+  worker_handle: WorkerHandle,
+  terminate_tx: mpsc::Sender<()>,
+  terminated: Arc<AtomicBool>,
+  isolate_handle: v8::IsolateHandle,
+}
+
+impl Deref for WebWorkerHandle {
+  type Target = WorkerHandle;
+  fn deref(&self) -> &Self::Target {
+    &self.worker_handle
+  }
+}
+
+impl DerefMut for WebWorkerHandle {
+  fn deref_mut(&mut self) -> &mut Self::Target {
+    &mut self.worker_handle
+  }
+}
+
+impl WebWorkerHandle {
+  pub fn terminate(&self) {
+    // This function can be called multiple times by whomever holds
+    // the handle. However only a single "termination" should occur so
+    // we need a guard here.
+    let already_terminated = self.terminated.swap(true, Ordering::Relaxed);
+
+    if !already_terminated {
+      self.isolate_handle.terminate_execution();
+      let mut sender = self.terminate_tx.clone();
+      // This call should be infallible hence the `expect`.
+      // This might change in the future.
+      sender.try_send(()).expect("Failed to terminate");
+    }
+  }
+}
+
 /// This worker is implementation of `Worker` Web API
 ///
 /// At the moment this type of worker supports only
@@ -23,17 +74,50 @@ use std::task::Poll;
 /// `WebWorker`.
 pub struct WebWorker {
   worker: Worker,
-  is_ready: bool,
+  event_loop_idle: bool,
+  terminate_rx: mpsc::Receiver<()>,
+  handle: WebWorkerHandle,
 }
 
 impl WebWorker {
   pub fn new(name: String, startup_data: StartupData, state: State) -> Self {
     let state_ = state.clone();
     let mut worker = Worker::new(name, startup_data, state_);
+
+    let terminated = Arc::new(AtomicBool::new(false));
+    let isolate_handle = worker
+      .isolate
+      .v8_isolate
+      .as_mut()
+      .unwrap()
+      .thread_safe_handle();
+    let (terminate_tx, terminate_rx) = mpsc::channel::<()>(1);
+
+    let handle = WebWorkerHandle {
+      worker_handle: worker.thread_safe_handle(),
+      terminated,
+      isolate_handle,
+      terminate_tx,
+    };
+
+    let mut web_worker = Self {
+      worker,
+      event_loop_idle: false,
+      terminate_rx,
+      handle,
+    };
+
+    let handle = web_worker.thread_safe_handle();
+
     {
-      let isolate = &mut worker.isolate;
+      let isolate = &mut web_worker.worker.isolate;
       ops::runtime::init(isolate, &state);
-      ops::web_worker::init(isolate, &state, &worker.internal_channels.sender);
+      ops::web_worker::init(
+        isolate,
+        &state,
+        &web_worker.worker.internal_channels.sender,
+        handle,
+      );
       ops::worker_host::init(isolate, &state);
       ops::io::init(isolate, &state);
       ops::resources::init(isolate, &state);
@@ -42,10 +126,14 @@ impl WebWorker {
       ops::fetch::init(isolate, &state);
     }
 
-    Self {
-      worker,
-      is_ready: false,
-    }
+    web_worker
+  }
+}
+
+impl WebWorker {
+  /// Returns a way to communicate with the Worker from other threads.
+  pub fn thread_safe_handle(&self) -> WebWorkerHandle {
+    self.handle.clone()
   }
 }
 
@@ -69,47 +157,67 @@ impl Future for WebWorker {
     let inner = self.get_mut();
     let worker = &mut inner.worker;
 
-    if !inner.is_ready {
+    let terminated = inner.handle.terminated.load(Ordering::Relaxed);
+
+    if terminated {
+      return Poll::Ready(Ok(()));
+    }
+
+    if !inner.event_loop_idle {
       match worker.poll_unpin(cx) {
         Poll::Ready(r) => {
+          let terminated = inner.handle.terminated.load(Ordering::Relaxed);
+          if terminated {
+            return Poll::Ready(Ok(()));
+          }
+
           if let Err(e) = r {
             let mut sender = worker.internal_channels.sender.clone();
-            futures::executor::block_on(sender.send(WorkerEvent::Error(e)))
+            sender
+              .try_send(WorkerEvent::Error(e))
               .expect("Failed to post message to host");
           }
-          inner.is_ready = true;
+          inner.event_loop_idle = true;
         }
         Poll::Pending => {}
       }
     }
 
-    let maybe_msg = {
-      match worker.internal_channels.receiver.poll_next_unpin(cx) {
-        Poll::Ready(r) => match r {
-          Some(msg) => {
-            let msg_str = String::from_utf8(msg.to_vec()).unwrap();
-            debug!("received message from host: {}", msg_str);
-            Some(msg_str)
-          }
-          None => {
-            debug!("channel closed by host, worker event loop shuts down");
-            return Poll::Ready(Ok(()));
+    if let Poll::Ready(r) = inner.terminate_rx.poll_next_unpin(cx) {
+      // terminate_rx should never be closed
+      assert!(r.is_some());
+      return Poll::Ready(Ok(()));
+    }
+
+    if let Poll::Ready(r) =
+      worker.internal_channels.receiver.poll_next_unpin(cx)
+    {
+      match r {
+        Some(msg) => {
+          let msg = String::from_utf8(msg.to_vec()).unwrap();
+          debug!("received message from host: {}", msg);
+          let script = format!("workerMessageRecvCallback({})", msg);
+
+          if let Err(e) = worker.execute(&script) {
+            // If execution was terminated during message callback then
+            // just ignore it
+            if inner.handle.terminated.load(Ordering::Relaxed) {
+              return Poll::Ready(Ok(()));
+            }
+
+            // Otherwise forward error to host
+            let mut sender = worker.internal_channels.sender.clone();
+            sender
+              .try_send(WorkerEvent::Error(e))
+              .expect("Failed to post message to host");
           }
-        },
-        Poll::Pending => None,
-      }
-    };
 
-    if let Some(msg) = maybe_msg {
-      // TODO: just add second value and then bind using rusty_v8
-      // to get structured clone/transfer working
-      let script = format!("workerMessageRecvCallback({})", msg);
-      worker
-        .execute(&script)
-        .expect("Failed to execute message cb");
-      // Let worker be polled again
-      inner.is_ready = false;
-      worker.waker.wake();
+          // Let event loop be polled again
+          inner.event_loop_idle = false;
+          worker.waker.wake();
+        }
+        None => unreachable!(),
+      }
     }
 
     Poll::Pending
@@ -123,7 +231,6 @@ mod tests {
   use crate::state::State;
   use crate::tokio_util;
   use crate::worker::WorkerEvent;
-  use crate::worker::WorkerHandle;
 
   fn create_test_worker() -> WebWorker {
     let state = State::mock("./hello.js");
@@ -138,7 +245,7 @@ mod tests {
   #[test]
   fn test_worker_messages() {
     let (handle_sender, handle_receiver) =
-      std::sync::mpsc::sync_channel::<WorkerHandle>(1);
+      std::sync::mpsc::sync_channel::<WebWorkerHandle>(1);
 
     let join_handle = std::thread::spawn(move || {
       let mut worker = create_test_worker();
@@ -165,13 +272,13 @@ mod tests {
 
     tokio_util::run_basic(async move {
       let msg = json!("hi").to_string().into_boxed_str().into_boxed_bytes();
-      let r = handle.post_message(msg.clone()).await;
+      let r = handle.post_message(msg.clone());
       assert!(r.is_ok());
 
       let maybe_msg = handle.get_event().await;
       assert!(maybe_msg.is_some());
 
-      let r = handle.post_message(msg.clone()).await;
+      let r = handle.post_message(msg.clone());
       assert!(r.is_ok());
 
       let maybe_msg = handle.get_event().await;
@@ -187,7 +294,7 @@ mod tests {
         .to_string()
         .into_boxed_str()
         .into_boxed_bytes();
-      let r = handle.post_message(msg).await;
+      let r = handle.post_message(msg);
       assert!(r.is_ok());
       let event = handle.get_event().await;
       assert!(event.is_none());
@@ -199,7 +306,7 @@ mod tests {
   #[test]
   fn removed_from_resource_table_on_close() {
     let (handle_sender, handle_receiver) =
-      std::sync::mpsc::sync_channel::<WorkerHandle>(1);
+      std::sync::mpsc::sync_channel::<WebWorkerHandle>(1);
 
     let join_handle = std::thread::spawn(move || {
       let mut worker = create_test_worker();
@@ -214,7 +321,7 @@ mod tests {
 
     tokio_util::run_basic(async move {
       let msg = json!("hi").to_string().into_boxed_str().into_boxed_bytes();
-      let r = handle.post_message(msg.clone()).await;
+      let r = handle.post_message(msg.clone());
       assert!(r.is_ok());
       let event = handle.get_event().await;
       assert!(event.is_none());
diff --git a/cli/worker.rs b/cli/worker.rs
index 9e1a646d5..c2a1ecc57 100644
--- a/cli/worker.rs
+++ b/cli/worker.rs
@@ -11,8 +11,6 @@ use deno_core::ModuleSpecifier;
 use deno_core::StartupData;
 use futures::channel::mpsc;
 use futures::future::FutureExt;
-use futures::future::TryFutureExt;
-use futures::sink::SinkExt;
 use futures::stream::StreamExt;
 use futures::task::AtomicWaker;
 use std::env;
@@ -32,6 +30,7 @@ use url::Url;
 pub enum WorkerEvent {
   Message(Buf),
   Error(ErrBox),
+  TerminalError(ErrBox),
 }
 
 pub struct WorkerChannelsInternal {
@@ -43,18 +42,13 @@ pub struct WorkerChannelsInternal {
 pub struct WorkerHandle {
   pub sender: mpsc::Sender<Buf>,
   pub receiver: Arc<AsyncMutex<mpsc::Receiver<WorkerEvent>>>,
-  // terminate_channel
 }
 
 impl WorkerHandle {
-  pub fn terminate(&self) {
-    todo!()
-  }
-
   /// Post message to worker as a host.
-  pub async fn post_message(&self, buf: Buf) -> Result<(), ErrBox> {
+  pub fn post_message(&self, buf: Buf) -> Result<(), ErrBox> {
     let mut sender = self.sender.clone();
-    sender.send(buf).map_err(ErrBox::from).await
+    sender.try_send(buf).map_err(ErrBox::from)
   }
 
   // TODO: should use `try_lock` and return error if
@@ -205,6 +199,7 @@ impl Future for Worker {
 
   fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
     let inner = self.get_mut();
+
     if let Some(deno_inspector) = inner.inspector.as_mut() {
       // We always poll the inspector if it exists.
       let _ = deno_inspector.poll_unpin(cx);
@@ -249,7 +244,6 @@ impl MainWorker {
       ops::timers::init(isolate, &state);
       ops::tty::init(isolate, &state);
       ops::worker_host::init(isolate, &state);
-      ops::web_worker::init(isolate, &state, &worker.internal_channels.sender);
     }
     Self(worker)
   }