6 files changed, 65 insertions, 18 deletions
diff --git a/cli/tests/integration/run_tests.rs b/cli/tests/integration/run_tests.rs
index df92ad422..5116db295 100644
--- a/cli/tests/integration/run_tests.rs
+++ b/cli/tests/integration/run_tests.rs
@@ -1188,6 +1188,12 @@ itest!(worker_close_race {
   output: "worker_close_race.js.out",
 });
 
+itest!(worker_drop_handle_race {
+  args: "run --quiet --reload --allow-read worker_drop_handle_race.js",
+  output: "worker_drop_handle_race.js.out",
+  exit_code: 1,
+});
+
 itest!(worker_message_before_close {
   args: "run --quiet --reload --allow-read worker_message_before_close.js",
   output: "worker_message_before_close.js.out",
diff --git a/cli/tests/testdata/worker_drop_handle_race.js b/cli/tests/testdata/worker_drop_handle_race.js
new file mode 100644
index 000000000..d637ac8c2
--- /dev/null
+++ b/cli/tests/testdata/worker_drop_handle_race.js
@@ -0,0 +1,12 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+// https://github.com/denoland/deno/issues/11342
+// Test for a panic that happens when the main thread's event loop finishes
+// running while the worker's event loop is still spinning.
+
+// The exception thrown in the worker will not terminate the worker, but it will
+// propagate to the main thread and cause it to exit.
+new Worker(
+  new URL("./workers/drop_handle_race.js", import.meta.url).href,
+  { type: "module" },
+);
diff --git a/cli/tests/testdata/worker_drop_handle_race.js.out b/cli/tests/testdata/worker_drop_handle_race.js.out
new file mode 100644
index 000000000..71dfde620
--- /dev/null
+++ b/cli/tests/testdata/worker_drop_handle_race.js.out
@@ -0,0 +1,8 @@
+error: Uncaught (in worker "") Error
+  throw new Error();
+        ^
+    at [WILDCARD]/workers/drop_handle_race.js:2:9
+    at fire (deno:ext/timers/[WILDCARD])
+    at handleTimerMacrotask (deno:ext/timers/[WILDCARD])
+error: Uncaught (in promise) Error: Unhandled error event reached main worker.
+    at Worker.#pollControl (deno:runtime/js/11_workers.js:[WILDCARD])
diff --git a/cli/tests/testdata/workers/drop_handle_race.js b/cli/tests/testdata/workers/drop_handle_race.js
new file mode 100644
index 000000000..30676a600
--- /dev/null
+++ b/cli/tests/testdata/workers/drop_handle_race.js
@@ -0,0 +1,3 @@
+setTimeout(() => {
+  throw new Error();
+}, 1000);
diff --git a/runtime/ops/worker_host.rs b/runtime/ops/worker_host.rs
index 829681ab6..f749e495c 100644
--- a/runtime/ops/worker_host.rs
+++ b/runtime/ops/worker_host.rs
@@ -65,7 +65,8 @@ pub type CreateWebWorkerCb = dyn Fn(CreateWebWorkerArgs) -> (WebWorker, Sendable
 pub struct CreateWebWorkerCbHolder(Arc<CreateWebWorkerCb>);
 
 pub struct WorkerThread {
-  join_handle: JoinHandle<Result<(), AnyError>>,
+  // It's an Option so we can take the value before dropping the WorkerThread.
+  join_handle: Option<JoinHandle<Result<(), AnyError>>>,
   worker_handle: WebWorkerHandle,
 
   // A WorkerThread that hasn't been explicitly terminated can only be removed
@@ -75,6 +76,34 @@ pub struct WorkerThread {
   message_closed: bool,
 }
 
+impl WorkerThread {
+  fn terminate(mut self) {
+    self.worker_handle.clone().terminate();
+    self
+      .join_handle
+      .take()
+      .unwrap()
+      .join()
+      .expect("Worker thread panicked")
+      .expect("Panic in worker event loop");
+
+    // Optimization so the Drop impl doesn't try to terminate the worker handle
+    // again.
+    self.ctrl_closed = true;
+    self.message_closed = true;
+  }
+}
+
+impl Drop for WorkerThread {
+  fn drop(&mut self) {
+    // If either of the channels is closed, the worker thread has at least
+    // started closing, and its event loop won't start another run.
+    if !(self.ctrl_closed || self.message_closed) {
+      self.worker_handle.clone().terminate();
+    }
+  }
+}
+
 pub type WorkersTable = HashMap<WorkerId, WorkerThread>;
 
 pub fn init(create_web_worker_cb: Arc<CreateWebWorkerCb>) -> Extension {
@@ -557,7 +586,7 @@ fn op_create_worker(
   let worker_handle = handle_receiver.recv().unwrap()?;
 
   let worker_thread = WorkerThread {
-    join_handle,
+    join_handle: Some(join_handle),
     worker_handle: worker_handle.into(),
     ctrl_closed: false,
     message_closed: false,
@@ -578,12 +607,7 @@ fn op_host_terminate_worker(
   _: (),
 ) -> Result<(), AnyError> {
   if let Some(worker_thread) = state.borrow_mut::<WorkersTable>().remove(&id) {
-    worker_thread.worker_handle.terminate();
-    worker_thread
-      .join_handle
-      .join()
-      .expect("Panic in worker thread")
-      .expect("Panic in worker event loop");
+    worker_thread.terminate();
   } else {
     debug!("tried to terminate non-existent worker {}", id);
   }
@@ -625,13 +649,7 @@ fn close_channel(
     };
 
     if terminate {
-      let worker_thread = entry.remove();
-      worker_thread.worker_handle.terminate();
-      worker_thread
-        .join_handle
-        .join()
-        .expect("Worker thread panicked")
-        .expect("Panic in worker event loop");
+      entry.remove().terminate();
     }
   }
 }
diff --git a/runtime/web_worker.rs b/runtime/web_worker.rs
index 975028b16..07f6facc5 100644
--- a/runtime/web_worker.rs
+++ b/runtime/web_worker.rs
@@ -206,9 +206,9 @@ impl WebWorkerHandle {
   /// Terminate the worker
   /// This function will set terminated to true, terminate the isolate and close the message channel
   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.
+    // A WebWorkerHandle can be terminated / dropped after `self.close()` has
+    // been called inside the worker, but only a single "termination" can occur,
+    // so we need a guard here.
     let already_terminated = self.terminated.swap(true, Ordering::SeqCst);
 
     if !already_terminated {