Fix deadlock detection failing during exceptions

Author: andrewgodwin

asgiref/sync.py

@@ -427,25 +427,27 @@ async def __call__(self, *args, **kwargs):
         else:
             func = self.func
 
-        # Run the code in the right thread
-        future = loop.run_in_executor(
-            executor,
-            functools.partial(
-                self.thread_handler,
-                loop,
-                self.get_current_task(),
-                sys.exc_info(),
-                func,
-                *args,
-                **kwargs,
-            ),
-        )
-        ret = await asyncio.wait_for(future, timeout=None)
+        try:
+            # Run the code in the right thread
+            future = loop.run_in_executor(
+                executor,
+                functools.partial(
+                    self.thread_handler,
+                    loop,
+                    self.get_current_task(),
+                    sys.exc_info(),
+                    func,
+                    *args,
+                    **kwargs,
+                ),
+            )
+            ret = await asyncio.wait_for(future, timeout=None)
 
-        if contextvars is not None:
-            _restore_context(context)
-        if self.deadlock_context:
-            self.deadlock_context.set(False)
+        finally:
+            if contextvars is not None:
+                _restore_context(context)
+            if self.deadlock_context:
+                self.deadlock_context.set(False)
 
         return ret
 

tests/test_sync.py

@@ -694,3 +694,26 @@ async def server_entry():
 
     with pytest.raises(RuntimeError):
         asyncio.run(server_entry())
+
+
+@pytest.mark.skipif(sys.version_info < (3, 7), reason="Issue persists with 3.6")
+def test_sync_to_async_deadlock_ignored_with_exception():
+    """
+    Ensures that throwing an exception from inside a deadlock-protected block
+    still resets the deadlock detector's status.
+    """
+
+    def view():
+        raise ValueError()
+
+    async def server_entry():
+        try:
+            await sync_to_async(view)()
+        except ValueError:
+            pass
+        try:
+            await sync_to_async(view)()
+        except ValueError:
+            pass
+
+    asyncio.run(server_entry())