From 2fbd4793c182d20dd34b0ca4319e02b9ff4fdf81 Mon Sep 17 00:00:00 2001
From: Nikolai Ryzhkov <dev@namezys.com>
Date: Fri, 28 Feb 2025 11:48:12 +0100
Subject: [PATCH 1/3] Reproduce issue #495

---
 tests/test_sync.py | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tests/test_sync.py b/tests/test_sync.py
index 0c67308c..ef5391c1 100644
--- a/tests/test_sync.py
+++ b/tests/test_sync.py
@@ -8,7 +8,7 @@
 from concurrent.futures import ThreadPoolExecutor
 from functools import wraps
 from typing import Any
-from unittest import TestCase
+from unittest import TestCase, mock
 
 import pytest
 
@@ -197,6 +197,22 @@ def test_method(self):
     assert method.__self__ == instance
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("exc_cls", (RuntimeError, ValueError, Exception))
+async def test_sync_to_async_broken_executor(exc_cls):
+    """
+    Tests sync_to_async catch error in executor and avoid deadlock
+    """
+    with mock.patch.object(ThreadPoolExecutor, "submit") as mock_run:
+        mock_run.side_effect = exc_cls("Test Error")
+        async_function = sync_to_async(lambda: None, thread_sensitive=True)
+        with pytest.raises(exc_cls, match="Test Error"):
+            await async_function()
+        with pytest.raises(exc_cls, match="Test Error"):
+            await async_function()
+
+
+
 @pytest.mark.asyncio
 async def test_async_to_sync_to_async():
     """

From 30039d1bc27ddc60bfe43e28145dcaec7b44eb70 Mon Sep 17 00:00:00 2001
From: Nikolai Ryzhkov <dev@namezys.com>
Date: Fri, 28 Feb 2025 11:50:03 +0100
Subject: [PATCH 2/3] Rollback state of SyncToAsync if loop.run_in_executor
 raises an exception

---
 asgiref/sync.py | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/asgiref/sync.py b/asgiref/sync.py
index 377075d1..82c8279d 100644
--- a/asgiref/sync.py
+++ b/asgiref/sync.py
@@ -452,22 +452,29 @@ async def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _R:
         func = context.run
         task_context: List[asyncio.Task[Any]] = []
 
-        # Run the code in the right thread
-        exec_coro = loop.run_in_executor(
-            executor,
-            functools.partial(
-                self.thread_handler,
-                loop,
-                sys.exc_info(),
-                task_context,
-                func,
-                child,
-            ),
-        )
+        try:
+            # Run the code in the right thread
+            exec_coro = loop.run_in_executor(
+                executor,
+                functools.partial(
+                    self.thread_handler,
+                    loop,
+                    sys.exc_info(),
+                    task_context,
+                    func,
+                    child,
+                ),
+            )
+        except:
+            _restore_context(context)
+            self.deadlock_context.set(False)
+            raise
+
         ret: _R
         try:
             ret = await asyncio.shield(exec_coro)
         except asyncio.CancelledError:
+            # catch CancelledError only in await
             cancel_parent = True
             try:
                 task = task_context[0]

From c8ce675b99e8f0c1d54fb9d2506dc71ad0c7775b Mon Sep 17 00:00:00 2001
From: Nikolai Ryzhkov <dev@namezys.com>
Date: Fri, 28 Feb 2025 12:27:30 +0100
Subject: [PATCH 3/3] Style fix

---
 asgiref/sync.py    | 2 +-
 tests/test_sync.py | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/asgiref/sync.py b/asgiref/sync.py
index 82c8279d..7f9e6f50 100644
--- a/asgiref/sync.py
+++ b/asgiref/sync.py
@@ -465,7 +465,7 @@ async def __call__(self, *args: _P.args, **kwargs: _P.kwargs) -> _R:
                     child,
                 ),
             )
-        except:
+        except Exception:
             _restore_context(context)
             self.deadlock_context.set(False)
             raise
diff --git a/tests/test_sync.py b/tests/test_sync.py
index ef5391c1..c8253c2b 100644
--- a/tests/test_sync.py
+++ b/tests/test_sync.py
@@ -212,7 +212,6 @@ async def test_sync_to_async_broken_executor(exc_cls):
             await async_function()
 
 
-
 @pytest.mark.asyncio
 async def test_async_to_sync_to_async():
     """