aiotools.shield_fg()

kvmd/aiotools.py

@@ -84,6 +84,47 @@ _RetvalT = TypeVar("_RetvalT")
 
 
 # =====
+class _ArmoredFuture(asyncio.Future):
+    def cancel(self, *_, **__) -> bool:  # type: ignore
+        # FIXME: Выяснить, почему это работает
+        return False
+
+    def forced_cancel(self) -> bool:
+        return super().cancel()
+
+
+def shield_fg(aw: Awaitable):  # type: ignore
+    # XXX: Копия asyncio.shield() с небольшими изменениями
+
+    inner = asyncio.ensure_future(aw)
+    if inner.done():
+        return inner
+    outer = _ArmoredFuture(loop=inner.get_loop())
+
+    def inner_done(_) -> None:  # type: ignore
+        if outer.cancelled():
+            if not inner.cancelled():
+                inner.exception()  # Mark inner's result as retrieved
+            return
+
+        if inner.cancelled():
+            outer.forced_cancel()
+        else:
+            err = inner.exception()
+            if err is not None:
+                outer.set_exception(err)
+            else:
+                outer.set_result(inner.result())
+
+    def outer_done(_) -> None:  # type: ignore
+        if not inner.done():
+            inner.remove_done_callback(inner_done)
+
+    inner.add_done_callback(inner_done)
+    outer.add_done_callback(outer_done)
+    return outer
+
+
 def atomic(func: _FunctionT) -> _FunctionT:
     @functools.wraps(func)
     async def wrapper(*args: Any, **kwargs: Any) -> Any:

testenv/tests/test_aiotools.py

@@ -22,9 +22,12 @@
 
 import asyncio
 
+from typing import List
+
 import pytest
 
 from kvmd.aiotools import AioExclusiveRegion
+from kvmd.aiotools import shield_fg
 
 
 # =====
@@ -115,3 +118,34 @@ async def test_fail__region__access_two() -> None:
     assert not region.is_busy()
     await region.exit()
     assert not region.is_busy()
+
+
+# =====
+@pytest.mark.asyncio
+async def test_ok__shield_fg() -> None:
+    ops: List[str] = []
+
+    async def foo(op: str, delay: float) -> None:  # pylint: disable=disallowed-name
+        await asyncio.sleep(delay)
+        ops.append(op)
+
+    async def bar() -> None:  # pylint: disable=disallowed-name
+        try:
+            try:
+                try:
+                    raise RuntimeError()
+                finally:
+                    await shield_fg(foo("foo1", 2.0))
+                    ops.append("foo1-noexc")
+            finally:
+                await shield_fg(foo("foo2", 1.0))
+                ops.append("foo2-noexc")
+        finally:
+            ops.append("done")
+
+    task = asyncio.create_task(bar())
+    await asyncio.sleep(0.1)
+    task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await task
+    assert ops == ["foo1", "foo2", "foo2-noexc", "done"]