improved exception handling/logging in _map

setup.cfg

@@ -1,6 +1,6 @@
 [metadata]
 name = asyncio-taskpool
-version = 1.0.0-beta
+version = 1.0.0
 author = Daniil Fajnberg
 author_email = [email protected]
 description = Dynamically manage pools of asyncio tasks
@@ -11,7 +11,7 @@ url = https://git.fajnberg.de/daniil/asyncio-taskpool
 project_urls =
     Bug Tracker = https://github.com/daniil-berg/asyncio-taskpool/issues
 classifiers =
-    Development Status :: 4 - Beta
+    Development Status :: 5 - Production/Stable
     Programming Language :: Python :: 3
     Operating System :: OS Independent
     License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)

src/asyncio_taskpool/pool.py

@@ -326,6 +326,8 @@ async def _start_task(self, awaitable: Awaitable, group_name: str = DEFAULT_TASK
         """
         self._check_start(awaitable=awaitable, ignore_lock=ignore_lock)
         await self._enough_room.acquire()
+        # TODO: Make sure that cancellation (group or pool) interrupts this method after context switching!
+        #       Possibly make use of the task group register for that.
         group_reg = self._task_groups.setdefault(group_name, TaskGroupRegister())
         async with group_reg:
             task_id = self._num_started
@@ -609,8 +611,7 @@ async def _apply_spawner(self, group_name: str, func: CoroutineFunc, args: ArgsT
             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)
+                log.debug("Cancelled group '%s' after %s out of %s tasks have been spawned", group_name, i, num)
                 coroutine.close()
                 return
 
@@ -707,29 +708,31 @@ async def _arg_consumer(self, group_name: str, num_concurrent: int, func: Corout
                 The callback that was specified to execute after cancellation of the task (and the next one).
                 It is run with the task's ID as its only positional argument.
         """
-        map_semaphore = Semaphore(num_concurrent)
-        release_cb = self._get_map_end_callback(map_semaphore, actual_end_callback=end_callback)
-        for next_arg in arg_iter:
-            # 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`).
+        semaphore = Semaphore(num_concurrent)
+        release_cb = self._get_map_end_callback(semaphore, actual_end_callback=end_callback)
+        for i, next_arg in enumerate(arg_iter):
+            semaphore_acquired = False
             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)
+                coroutine = star_function(func, next_arg, arg_stars=arg_stars)
+            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__, '*' * arg_stars, str(next_arg))
+                continue
+            try:
+                # 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.
+                semaphore_acquired = await semaphore.acquire()
+                await self._start_task(coroutine, group_name=group_name, ignore_lock=True,
+                                       end_callback=release_cb, cancel_callback=cancel_callback)
             except CancelledError:
-                # This means that no more tasks are supposed to be created from this `arg_iter`;
-                # thus, we can forget about the rest of the arguments.
-                log.debug("Cancelled consumption of argument iterable in task group '%s'", group_name)
-                map_semaphore.release()
+                # 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. (This means we drop `arg_iter` without consuming it fully.)
+                log.debug("Cancelled group '%s' after %s tasks have been spawned", group_name, i)
+                coroutine.close()
+                if semaphore_acquired:
+                    semaphore.release()
                 return
-            except Exception as e:
-                # This means an exception occurred during task **creation**, meaning no task has been created.
-                # It does not imply an error within the task itself.
-                log.exception("%s occurred while trying to create task: %s(%s%s)",
-                              str(e.__class__.__name__), func.__name__, '*' * arg_stars, str(next_arg))
-                map_semaphore.release()
 
     def _map(self, group_name: str, num_concurrent: int, func: CoroutineFunc, arg_iter: ArgsT, arg_stars: int,
              end_callback: EndCB = None, cancel_callback: CancelCB = None) -> None:
@@ -943,6 +946,7 @@ async def _start_num(self, num: int, group_name: str) -> None:
                              end_callback=self._end_callback, cancel_callback=self._cancel_callback)
             for _ in range(num)
         )
+        # TODO: Same deal as with the other meta tasks, provide proper cancellation handling!
         await gather(*start_coroutines)
 
     def start(self, num: int) -> str:

tests/test_pool.py

@@ -548,20 +548,20 @@ async def test__queue_consumer(self, mock_semaphore_cls: MagicMock, mock__get_ma
         n = 2
         mock_semaphore_cls.return_value = semaphore = Semaphore(n)
         mock__get_map_end_callback.return_value = map_cb = MagicMock()
-        awaitable = 'totally an awaitable'
-        mock_star_function.side_effect = [awaitable, Exception(), awaitable]
+        awaitable1, awaitable2 = 'totally an awaitable', object()
+        mock_star_function.side_effect = [awaitable1, Exception(), awaitable2]
         arg1, arg2, bad = 123456789, 'function argument', None
         args = [arg1, bad, arg2]
-        group_name, mock_func, stars = 'whatever', MagicMock(__name__="mock"), 3
+        grp_name, mock_func, stars = 'whatever', MagicMock(__name__="mock"), 3
         end_cb, cancel_cb = MagicMock(), MagicMock()
-        self.assertIsNone(await self.task_pool._arg_consumer(group_name, n, mock_func, args, stars, end_cb, cancel_cb))
-        # We expect the semaphore to be acquired 2 times, then be released once after the exception occurs, then
-        # acquired once more is reached. Since we initialized it with a value of 2, we expect it be locked.
+        self.assertIsNone(await self.task_pool._arg_consumer(grp_name, n, mock_func, args, stars, end_cb, cancel_cb))
+        # We initialized the semaphore with a value of 2. It should have been acquired twice. We expect it be locked.
         self.assertTrue(semaphore.locked())
         mock_semaphore_cls.assert_called_once_with(n)
         mock__get_map_end_callback.assert_called_once_with(semaphore, actual_end_callback=end_cb)
-        mock__start_task.assert_has_awaits(2 * [
-            call(awaitable, group_name=group_name, ignore_lock=True, end_callback=map_cb, cancel_callback=cancel_cb)
+        mock__start_task.assert_has_awaits([
+            call(awaitable1, group_name=grp_name, ignore_lock=True, end_callback=map_cb, cancel_callback=cancel_cb),
+            call(awaitable2, group_name=grp_name, ignore_lock=True, end_callback=map_cb, cancel_callback=cancel_cb),
         ])
         mock_star_function.assert_has_calls([
             call(mock_func, arg1, arg_stars=stars),
@@ -572,17 +572,50 @@ async def test__queue_consumer(self, mock_semaphore_cls: MagicMock, mock__get_ma
         mock_semaphore_cls.reset_mock()
         mock__get_map_end_callback.reset_mock()
         mock__start_task.reset_mock()
-        mock_star_function.reset_mock()
+        mock_star_function.reset_mock(side_effect=True)
+
+        # With a CancelledError thrown while acquiring the semaphore:
+        mock_acquire = AsyncMock(side_effect=[True, CancelledError])
+        mock_semaphore_cls.return_value = mock_semaphore = MagicMock(acquire=mock_acquire)
+        mock_star_function.return_value = mock_coroutine = MagicMock()
+        arg_it = iter(arg for arg in (arg1, arg2, FOO))
+        self.assertIsNone(await self.task_pool._arg_consumer(grp_name, n, mock_func, arg_it, stars, end_cb, cancel_cb))
+        mock_semaphore_cls.assert_called_once_with(n)
+        mock__get_map_end_callback.assert_called_once_with(mock_semaphore, actual_end_callback=end_cb)
+        mock_star_function.assert_has_calls([
+            call(mock_func, arg1, arg_stars=stars),
+            call(mock_func, arg2, arg_stars=stars)
+        ])
+        mock_acquire.assert_has_awaits([call(), call()])
+        mock__start_task.assert_awaited_once_with(mock_coroutine, group_name=grp_name, ignore_lock=True,
+                                                  end_callback=map_cb, cancel_callback=cancel_cb)
+        mock_coroutine.close.assert_called_once_with()
+        mock_semaphore.release.assert_not_called()
+        self.assertEqual(FOO, next(arg_it))
+
+        mock_acquire.reset_mock(side_effect=True)
+        mock_semaphore_cls.reset_mock()
+        mock__get_map_end_callback.reset_mock()
+        mock__start_task.reset_mock()
+        mock_star_function.reset_mock(side_effect=True)
 
-        # With a CancelledError thrown while starting a task:
-        mock_semaphore_cls.return_value = semaphore = Semaphore(1)
-        mock_star_function.side_effect = CancelledError()
-        self.assertIsNone(await self.task_pool._arg_consumer(group_name, n, mock_func, args, stars, end_cb, cancel_cb))
-        self.assertFalse(semaphore.locked())
+        # With a CancelledError thrown while starting the task:
+        mock__start_task.side_effect = [None, CancelledError]
+        arg_it = iter(arg for arg in (arg1, arg2, FOO))
+        self.assertIsNone(await self.task_pool._arg_consumer(grp_name, n, mock_func, arg_it, stars, end_cb, cancel_cb))
         mock_semaphore_cls.assert_called_once_with(n)
-        mock__get_map_end_callback.assert_called_once_with(semaphore, actual_end_callback=end_cb)
-        mock__start_task.assert_not_called()
-        mock_star_function.assert_called_once_with(mock_func, arg1, arg_stars=stars)
+        mock__get_map_end_callback.assert_called_once_with(mock_semaphore, actual_end_callback=end_cb)
+        mock_star_function.assert_has_calls([
+            call(mock_func, arg1, arg_stars=stars),
+            call(mock_func, arg2, arg_stars=stars)
+        ])
+        mock_acquire.assert_has_awaits([call(), call()])
+        mock__start_task.assert_has_awaits(2 * [
+            call(mock_coroutine, group_name=grp_name, ignore_lock=True, end_callback=map_cb, cancel_callback=cancel_cb)
+        ])
+        mock_coroutine.close.assert_called_once_with()
+        mock_semaphore.release.assert_called_once_with()
+        self.assertEqual(FOO, next(arg_it))
 
     @patch.object(pool, 'create_task')
     @patch.object(pool.TaskPool, '_arg_consumer', new_callable=MagicMock)