Test that start_blocking_portal doesn't deadlock when used by async t…

…hreads

pyproject.toml

@@ -48,6 +48,7 @@ test = [
     "hypothesis >= 4.0",
     "pytest >= 7.0",
     "pytest-mock >= 3.6.1",
+    "pytest-timeout >= 2.0",
     "trustme",
     "uvloop >= 0.17; platform_python_implementation == 'CPython' and platform_system != 'Windows'",
 ]

tests/test_from_thread.py

@@ -26,6 +26,9 @@
 from anyio.abc import TaskStatus
 from anyio.from_thread import BlockingPortal, start_blocking_portal
 from anyio.lowlevel import checkpoint
+from anyio.pytest_plugin import anyio_backend_name, anyio_backend_options
+
+from .conftest import anyio_backend
 
 if sys.version_info >= (3, 8):
     from typing import Literal
@@ -63,6 +66,23 @@ def thread_worker_sync(func: Callable[..., T_Retval], *args: Any) -> T_Retval:
     return from_thread.run_sync(func, *args)
 
 
+# Duplicate anyio_backend for BlockingPortal tests that need to be parametrized with
+# pairs of backends.
+portal_backend = anyio_backend
+
+
+@pytest.fixture
+def portal_backend_name(portal_backend: Any) -> str:
+    return anyio_backend_name.__wrapped__(portal_backend)  # type: ignore[attr-defined]
+
+
+@pytest.fixture
+def portal_backend_options(portal_backend: Any) -> dict[str, Any]:
+    return anyio_backend_options.__wrapped__(  # type: ignore[attr-defined]
+        portal_backend
+    )
+
+
 class TestRunAsyncFromThread:
     async def test_run_corofunc_from_thread(self) -> None:
         result = await to_thread.run_sync(thread_worker_async, async_add, 1, 2)
@@ -524,3 +544,13 @@ async def raise_baseexception() -> None:
                     portal.call(raise_baseexception)
 
                 assert exc.value.__context__ is None
+
+    @pytest.mark.timeout(1)
+    async def test_from_async(
+        self, portal_backend_name: str, portal_backend_options: dict[str, Any]
+    ) -> None:
+        """Test that portals don't deadlock when started/used from async code."""
+        with start_blocking_portal(
+            portal_backend_name, portal_backend_options
+        ) as portal:
+            portal.call(checkpoint)