Implements a task scheduler for resumable potentially long running tasks (#15891)

1 files changed, 186 insertions, 0 deletions

diff --git a/tests/util/test_task_scheduler.py b/tests/util/test_task_scheduler.py
new file mode 100644
index 0000000000..3a97559bf0
--- /dev/null
+++ b/tests/util/test_task_scheduler.py
@@ -0,0 +1,186 @@
+# Copyright 2023 The Matrix.org Foundation C.I.C.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from typing import Optional, Tuple
+
+from twisted.internet.task import deferLater
+from twisted.test.proto_helpers import MemoryReactor
+
+from synapse.server import HomeServer
+from synapse.types import JsonMapping, ScheduledTask, TaskStatus
+from synapse.util import Clock
+from synapse.util.task_scheduler import TaskScheduler
+
+from tests import unittest
+
+
+class TestTaskScheduler(unittest.HomeserverTestCase):
+    def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
+        self.task_scheduler = hs.get_task_scheduler()
+        self.task_scheduler.register_action(self._test_task, "_test_task")
+        self.task_scheduler.register_action(self._sleeping_task, "_sleeping_task")
+        self.task_scheduler.register_action(self._raising_task, "_raising_task")
+        self.task_scheduler.register_action(self._resumable_task, "_resumable_task")
+
+    async def _test_task(
+        self, task: ScheduledTask, first_launch: bool
+    ) -> Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]:
+        # This test task will copy the parameters to the result
+        result = None
+        if task.params:
+            result = task.params
+        return (TaskStatus.COMPLETE, result, None)
+
+    def test_schedule_task(self) -> None:
+        """Schedule a task in the future with some parameters to be copied as a result and check it executed correctly.
+        Also check that it get removed after `KEEP_TASKS_FOR_MS`."""
+        timestamp = self.clock.time_msec() + 30 * 1000
+        task_id = self.get_success(
+            self.task_scheduler.schedule_task(
+                "_test_task",
+                timestamp=timestamp,
+                params={"val": 1},
+            )
+        )
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        assert task is not None
+        self.assertEqual(task.status, TaskStatus.SCHEDULED)
+        self.assertIsNone(task.result)
+
+        # The timestamp being 30s after now the task should been executed
+        # after the first scheduling loop is run
+        self.reactor.advance(TaskScheduler.SCHEDULE_INTERVAL_MS / 1000)
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        assert task is not None
+        self.assertEqual(task.status, TaskStatus.COMPLETE)
+        assert task.result is not None
+        # The passed parameter should have been copied to the result
+        self.assertTrue(task.result.get("val") == 1)
+
+        # Let's wait for the complete task to be deleted and hence unavailable
+        self.reactor.advance((TaskScheduler.KEEP_TASKS_FOR_MS / 1000) + 1)
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        self.assertIsNone(task)
+
+    async def _sleeping_task(
+        self, task: ScheduledTask, first_launch: bool
+    ) -> Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]:
+        # Sleep for a second
+        await deferLater(self.reactor, 1, lambda: None)
+        return TaskStatus.COMPLETE, None, None
+
+    def test_schedule_lot_of_tasks(self) -> None:
+        """Schedule more than `TaskScheduler.MAX_CONCURRENT_RUNNING_TASKS` tasks and check the behavior."""
+        timestamp = self.clock.time_msec() + 30 * 1000
+        task_ids = []
+        for i in range(TaskScheduler.MAX_CONCURRENT_RUNNING_TASKS + 1):
+            task_ids.append(
+                self.get_success(
+                    self.task_scheduler.schedule_task(
+                        "_sleeping_task",
+                        timestamp=timestamp,
+                        params={"val": i},
+                    )
+                )
+            )
+
+        # The timestamp being 30s after now the task should been executed
+        # after the first scheduling loop is run
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000))
+
+        # This is to give the time to the sleeping tasks to finish
+        self.reactor.advance(1)
+
+        # Check that only MAX_CONCURRENT_RUNNING_TASKS tasks has run and that one
+        # is still scheduled.
+        tasks = [
+            self.get_success(self.task_scheduler.get_task(task_id))
+            for task_id in task_ids
+        ]
+
+        self.assertEquals(
+            len(
+                [t for t in tasks if t is not None and t.status == TaskStatus.COMPLETE]
+            ),
+            TaskScheduler.MAX_CONCURRENT_RUNNING_TASKS,
+        )
+
+        scheduled_tasks = [
+            t for t in tasks if t is not None and t.status == TaskStatus.SCHEDULED
+        ]
+        self.assertEquals(len(scheduled_tasks), 1)
+
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000))
+        self.reactor.advance(1)
+
+        # Check that the last task has been properly executed after the next scheduler loop run
+        prev_scheduled_task = self.get_success(
+            self.task_scheduler.get_task(scheduled_tasks[0].id)
+        )
+        assert prev_scheduled_task is not None
+        self.assertEquals(
+            prev_scheduled_task.status,
+            TaskStatus.COMPLETE,
+        )
+
+    async def _raising_task(
+        self, task: ScheduledTask, first_launch: bool
+    ) -> Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]:
+        raise Exception("raising")
+
+    def test_schedule_raising_task(self) -> None:
+        """Schedule a task raising an exception and check it runs to failure and report exception content."""
+        task_id = self.get_success(self.task_scheduler.schedule_task("_raising_task"))
+
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000))
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        assert task is not None
+        self.assertEqual(task.status, TaskStatus.FAILED)
+        self.assertEqual(task.error, "raising")
+
+    async def _resumable_task(
+        self, task: ScheduledTask, first_launch: bool
+    ) -> Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]:
+        if task.result and "in_progress" in task.result:
+            return TaskStatus.COMPLETE, {"success": True}, None
+        else:
+            await self.task_scheduler.update_task(task.id, result={"in_progress": True})
+            # Await forever to simulate an aborted task because of a restart
+            await deferLater(self.reactor, 2**16, lambda: None)
+            # This should never been called
+            return TaskStatus.ACTIVE, None, None
+
+    def test_schedule_resumable_task(self) -> None:
+        """Schedule a resumable task and check that it gets properly resumed and complete after simulating a synapse restart."""
+        task_id = self.get_success(self.task_scheduler.schedule_task("_resumable_task"))
+
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000))
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        assert task is not None
+        self.assertEqual(task.status, TaskStatus.ACTIVE)
+
+        # Simulate a synapse restart by emptying the list of running tasks
+        self.task_scheduler._running_tasks = set()
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000))
+
+        task = self.get_success(self.task_scheduler.get_task(task_id))
+        assert task is not None
+        self.assertEqual(task.status, TaskStatus.COMPLETE)
+        assert task.result is not None
+        self.assertTrue(task.result.get("success"))