improved exception handling/logging in apply meta task

src/asyncio_taskpool/internals/types.py

@@ -23,7 +23,7 @@ This module should **not** be considered part of the public API.
 
 from asyncio.streams import StreamReader, StreamWriter
 from pathlib import Path
-from typing import Any, Awaitable, Callable, Iterable, Mapping, Tuple, TypeVar, Union
+from typing import Any, Awaitable, Callable, Coroutine, Iterable, Mapping, Tuple, TypeVar, Union
 
 
 T = TypeVar('T')
@@ -32,7 +32,7 @@ ArgsT = Iterable[Any]
 KwArgsT = Mapping[str, Any]
 
 AnyCallableT = Callable[[...], Union[T, Awaitable[T]]]
-CoroutineFunc = Callable[[...], Awaitable[Any]]
+CoroutineFunc = Callable[[...], Coroutine]
 
 EndCB = Callable
 CancelCB = Callable

src/asyncio_taskpool/pool.py

@@ -528,6 +528,8 @@ class BaseTaskPool:
         self._tasks_cancelled.clear()
         self._tasks_running.clear()
         self._closed = True
+        # TODO: Turn the `_closed` attribute into an `Event` and add something like a `until_closed` method that will
+        #       await it to allow blocking until a closing command comes from a server.
 
 
 class TaskPool(BaseTaskPool):
@@ -566,36 +568,51 @@ class TaskPool(BaseTaskPool):
                 return name
             i += 1
 
-    async def _apply_num(self, group_name: str, func: CoroutineFunc, args: ArgsT = (), kwargs: KwArgsT = None,
+    async def _apply_spawner(self, group_name: str, func: CoroutineFunc, args: ArgsT = (), kwargs: KwArgsT = None,
-                         num: int = 1, end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
+                             num: int = 1, end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
         """
-        Creates a coroutine with the supplied arguments and runs it as a new task in the pool.
+        Creates coroutines with the supplied arguments and runs them as new tasks in the pool.
 
         This method blocks, **only if** the pool has not enough room to accommodate `num` new tasks.
 
         Args:
             group_name:
-                Name of the task group to add the new task to.
+                Name of the task group to add the new tasks to.
             func:
-                The coroutine function to be run as a task within the task pool.
+                The coroutine function to be run in `num` tasks within the task pool.
             args (optional):
-                The positional arguments to pass into the function call.
+                The positional arguments to pass into each function call.
             kwargs (optional):
-                The keyword-arguments to pass into the function call.
+                The keyword-arguments to pass into each function call.
             num (optional):
                 The number of tasks to spawn with the specified parameters.
             end_callback (optional):
-                A callback to execute after the task has ended.
+                A callback to execute after each task has ended.
                 It is run with the task's ID as its only positional argument.
             cancel_callback (optional):
-                A callback to execute after cancellation of the task.
+                A callback to execute after cancellation of each task.
                 It is run with the task's ID as its only positional argument.
         """
         if kwargs is None:
             kwargs = {}
-        # TODO: Add exception logging
+        for i in range(num):
-        await gather(*(self._start_task(func(*args, **kwargs), group_name=group_name, end_callback=end_callback,
+            try:
-                                        cancel_callback=cancel_callback) for _ in range(num)))
+                coroutine = func(*args, **kwargs)
+            except Exception as e:
+                # This means there was probably something wrong with the function arguments.
+                log.exception("%s occurred in group '%s' while trying to create coroutine: %s(*%s, **%s)",
+                              str(e.__class__.__name__), group_name, func.__name__, repr(args), repr(kwargs))
+                continue
+            try:
+                await self._start_task(coroutine, group_name=group_name, end_callback=end_callback,
+                                       cancel_callback=cancel_callback)
+            except CancelledError:
+                # Either the task group or all tasks were cancelled, so this meta tasks is not supposed to spawn any
+                # more tasks and can return immediately.
+                log.debug("Cancelled spawning tasks in group '%s' after %s out of %s tasks have been spawned",
+                          group_name, i, num)
+                coroutine.close()
+                return
 
     def apply(self, func: CoroutineFunc, args: ArgsT = (), kwargs: KwArgsT = None, num: int = 1, group_name: str = None,
               end_callback: EndCB = None, cancel_callback: CancelCB = None) -> str:
@@ -650,8 +667,8 @@ class TaskPool(BaseTaskPool):
             raise exceptions.InvalidGroupName(f"Group named {group_name} already exists!")
         self._task_groups.setdefault(group_name, TaskGroupRegister())
         meta_tasks = self._group_meta_tasks_running.setdefault(group_name, set())
-        meta_tasks.add(create_task(self._apply_num(group_name, func, args, kwargs, num,
+        meta_tasks.add(create_task(self._apply_spawner(group_name, func, args, kwargs, num,
-                                                   end_callback=end_callback, cancel_callback=cancel_callback)))
+                                                       end_callback=end_callback, cancel_callback=cancel_callback)))
         return group_name
 
     @staticmethod
@@ -696,6 +713,8 @@ class TaskPool(BaseTaskPool):
             # When the number of running tasks spawned by this method reaches the specified maximum,
             # this next line will block, until one of them ends and releases the semaphore.
             await map_semaphore.acquire()
+            # TODO: Clean up exception handling/logging. Cancellation can also occur while awaiting the semaphore.
+            #       Wrap `star_function` call in a separate `try` block (similar to `_apply_spawner`).
             try:
                 await self._start_task(star_function(func, next_arg, arg_stars=arg_stars), group_name=group_name,
                                        ignore_lock=True, end_callback=release_cb, cancel_callback=cancel_callback)

tests/test_pool.py

@@ -455,49 +455,65 @@ class TaskPoolTestCase(CommonTestCase):
         self.assertEqual(expected_output, output)
 
     @patch.object(pool.TaskPool, '_start_task')
-    async def test__apply_num(self, mock__start_task: AsyncMock):
+    async def test__apply_spawner(self, mock__start_task: AsyncMock):
-        group_name = FOO + BAR
+        grp_name = FOO + BAR
-        mock_awaitable = object()
+        mock_awaitable1, mock_awaitable2 = object(), object()
-        mock_func = MagicMock(return_value=mock_awaitable)
+        mock_func = MagicMock(side_effect=[mock_awaitable1, Exception(), mock_awaitable2], __name__='func')
-        args, kwargs, num = (FOO, BAR), {'a': 1, 'b': 2}, 3
+        args, kw, num = (FOO, BAR), {'a': 1, 'b': 2}, 3
         end_cb, cancel_cb = MagicMock(), MagicMock()
-        self.assertIsNone(await self.task_pool._apply_num(group_name, mock_func, args, kwargs, num, end_cb, cancel_cb))
+        self.assertIsNone(await self.task_pool._apply_spawner(grp_name, mock_func, args, kw, num, end_cb, cancel_cb))
-        mock_func.assert_has_calls(3 * [call(*args, **kwargs)])
+        mock_func.assert_has_calls(num * [call(*args, **kw)])
-        mock__start_task.assert_has_awaits(3 * [
+        mock__start_task.assert_has_awaits([
-            call(mock_awaitable, group_name=group_name, end_callback=end_cb, cancel_callback=cancel_cb)
+            call(mock_awaitable1, group_name=grp_name, end_callback=end_cb, cancel_callback=cancel_cb),
+            call(mock_awaitable2, group_name=grp_name, end_callback=end_cb, cancel_callback=cancel_cb),
         ])
 
-        mock_func.reset_mock()
+        mock_func.reset_mock(side_effect=True)
         mock__start_task.reset_mock()
 
-        self.assertIsNone(await self.task_pool._apply_num(group_name, mock_func, args, None, num, end_cb, cancel_cb))
+        # Simulate cancellation while the second task is being started.
-        mock_func.assert_has_calls(num * [call(*args)])
+        mock__start_task.side_effect = [None, CancelledError, None]
-        mock__start_task.assert_has_awaits(num * [
+        mock_coroutine_to_close = MagicMock()
-            call(mock_awaitable, group_name=group_name, end_callback=end_cb, cancel_callback=cancel_cb)
+        mock_func.side_effect = [mock_awaitable1, mock_coroutine_to_close, 'never called']
+        self.assertIsNone(await self.task_pool._apply_spawner(grp_name, mock_func, args, None, num, end_cb, cancel_cb))
+        mock_func.assert_has_calls(2 * [call(*args)])
+        mock__start_task.assert_has_awaits([
+            call(mock_awaitable1, group_name=grp_name, end_callback=end_cb, cancel_callback=cancel_cb),
+            call(mock_coroutine_to_close, group_name=grp_name, end_callback=end_cb, cancel_callback=cancel_cb),
         ])
+        mock_coroutine_to_close.close.assert_called_once_with()
 
     @patch.object(pool, 'create_task')
-    @patch.object(pool.TaskPool, '_apply_num', new_callable=MagicMock())
+    @patch.object(pool.TaskPool, '_apply_spawner', new_callable=MagicMock())
     @patch.object(pool, 'TaskGroupRegister')
     @patch.object(pool.TaskPool, '_generate_group_name')
     @patch.object(pool.BaseTaskPool, '_check_start')
     def test_apply(self, mock__check_start: MagicMock, mock__generate_group_name: MagicMock,
-                   mock_reg_cls: MagicMock, mock__apply_num: MagicMock, mock_create_task: MagicMock):
+                   mock_reg_cls: MagicMock, mock__apply_spawner: MagicMock, mock_create_task: MagicMock):
         mock__generate_group_name.return_value = generated_name = 'name 123'
         mock_group_reg = set_up_mock_group_register(mock_reg_cls)
-        mock__apply_num.return_value = mock_apply_coroutine = object()
+        mock__apply_spawner.return_value = mock_apply_coroutine = object()
         mock_create_task.return_value = fake_task = object()
         mock_func, num, group_name = MagicMock(), 3, FOO + BAR
         args, kwargs = (FOO, BAR), {'a': 1, 'b': 2}
         end_cb, cancel_cb = MagicMock(), MagicMock()
+
+        self.task_pool._task_groups = {group_name: 'causes error'}
+        with self.assertRaises(exceptions.InvalidGroupName):
+            self.task_pool.apply(mock_func, args, kwargs, num, group_name, end_cb, cancel_cb)
+        mock__check_start.assert_called_once_with(function=mock_func)
+        mock__apply_spawner.assert_not_called()
+        mock_create_task.assert_not_called()
+
+        mock__check_start.reset_mock()
         self.task_pool._task_groups = {}
 
         def check_assertions(_group_name, _output):
             self.assertEqual(_group_name, _output)
             mock__check_start.assert_called_once_with(function=mock_func)
             self.assertEqual(mock_group_reg, self.task_pool._task_groups[_group_name])
-            mock__apply_num.assert_called_once_with(_group_name, mock_func, args, kwargs, num,
+            mock__apply_spawner.assert_called_once_with(_group_name, mock_func, args, kwargs, num,
-                                                    end_callback=end_cb, cancel_callback=cancel_cb)
+                                                        end_callback=end_cb, cancel_callback=cancel_cb)
             mock_create_task.assert_called_once_with(mock_apply_coroutine)
             self.assertSetEqual({fake_task}, self.task_pool._group_meta_tasks_running[group_name])
 
@@ -507,7 +523,7 @@ class TaskPoolTestCase(CommonTestCase):
 
         mock__check_start.reset_mock()
         self.task_pool._task_groups.clear()
-        mock__apply_num.reset_mock()
+        mock__apply_spawner.reset_mock()
         mock_create_task.reset_mock()
 
         output = self.task_pool.apply(mock_func, args, kwargs, num, None, end_cb, cancel_cb)
@@ -695,6 +711,7 @@ class SimpleTaskPoolTestCase(CommonTestCase):
 
     def tearDown(self) -> None:
         self.base_class_init_patcher.stop()
+        super().tearDown()
 
     def test_init(self):
         self.assertEqual(self.TEST_POOL_FUNC, self.task_pool._func)