Implements a task scheduler for resumable potentially long running tasks

changelog.d/15891.feature

@@ -0,0 +1 @@
+Implements a task scheduler for	resumable potentially long running tasks.

synapse/app/generic_worker.py

@@ -91,6 +91,7 @@ from synapse.storage.databases.main.state import StateGroupWorkerStore
 from synapse.storage.databases.main.stats import StatsStore
 from synapse.storage.databases.main.stream import StreamWorkerStore
 from synapse.storage.databases.main.tags import TagsWorkerStore
+from synapse.storage.databases.main.task_scheduler import TaskSchedulerWorkerStore
 from synapse.storage.databases.main.transactions import TransactionWorkerStore
 from synapse.storage.databases.main.ui_auth import UIAuthWorkerStore
 from synapse.storage.databases.main.user_directory import UserDirectoryStore
@@ -144,6 +145,7 @@ class GenericWorkerStore(
     TransactionWorkerStore,
     LockStore,
     SessionStore,
+    TaskSchedulerWorkerStore,
 ):
     # Properties that multiple storage classes define. Tell mypy what the
     # expected type is.

synapse/server.py

@@ -141,6 +141,7 @@ from synapse.util.distributor import Distributor
 from synapse.util.macaroons import MacaroonGenerator
 from synapse.util.ratelimitutils import FederationRateLimiter
 from synapse.util.stringutils import random_string
+from synapse.util.task_scheduler import TaskScheduler
 
 logger = logging.getLogger(__name__)
 
@@ -359,6 +360,7 @@ class HomeServer(metaclass=abc.ABCMeta):
         """
         for i in self.REQUIRED_ON_BACKGROUND_TASK_STARTUP:
             getattr(self, "get_" + i + "_handler")()
+        self.get_task_scheduler()
 
     def get_reactor(self) -> ISynapseReactor:
         """
@@ -912,3 +914,7 @@ class HomeServer(metaclass=abc.ABCMeta):
     def get_common_usage_metrics_manager(self) -> CommonUsageMetricsManager:
         """Usage metrics shared between phone home stats and the prometheus exporter."""
         return CommonUsageMetricsManager(self)
+
+    @cache_in_self
+    def get_task_scheduler(self) -> TaskScheduler:
+        return TaskScheduler(self)

synapse/storage/databases/main/__init__.py

@@ -70,6 +70,7 @@ from .state import StateStore
 from .stats import StatsStore
 from .stream import StreamWorkerStore
 from .tags import TagsStore
+from .task_scheduler import TaskSchedulerWorkerStore
 from .transactions import TransactionWorkerStore
 from .ui_auth import UIAuthStore
 from .user_directory import UserDirectoryStore
@@ -127,6 +128,7 @@ class DataStore(
     CacheInvalidationWorkerStore,
     LockStore,
     SessionStore,
+    TaskSchedulerWorkerStore,
 ):
     def __init__(
         self,

synapse/storage/databases/main/task_scheduler.py

@@ -0,0 +1,173 @@
+# 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.
+
+import json
+from typing import TYPE_CHECKING, Any, Dict, List, Optional
+
+from synapse.storage._base import SQLBaseStore
+from synapse.storage.database import DatabasePool, LoggingDatabaseConnection
+from synapse.types import JsonDict, JsonMapping, ScheduledTask, TaskStatus
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+
+class TaskSchedulerWorkerStore(SQLBaseStore):
+    def __init__(
+        self,
+        database: DatabasePool,
+        db_conn: LoggingDatabaseConnection,
+        hs: "HomeServer",
+    ):
+        super().__init__(database, db_conn, hs)
+
+    @staticmethod
+    def _convert_row_to_task(row: Dict[str, Any]) -> ScheduledTask:
+        row["status"] = TaskStatus(row["status"])
+        if row["params"] is not None:
+            row["params"] = json.loads(row["params"])
+        if row["result"] is not None:
+            row["result"] = json.loads(row["result"])
+        return ScheduledTask(**row)
+
+    async def get_scheduled_tasks(
+        self, action: Optional[str] = None, resource_id: Optional[str] = None
+    ) -> List[ScheduledTask]:
+        """Get a list of scheduled tasks from the DB.
+
+        If the parameters are `None` all the tasks are returned.
+
+        Args:
+            action: Limit the returned tasks to this specific action name
+            resource_id: Limit the returned tasks to this specific resource id
+
+        Returns: a list of `ScheduledTask`
+        """
+        keyvalues = {}
+        if action:
+            keyvalues["action"] = action
+        if resource_id:
+            keyvalues["resource_id"] = resource_id
+
+        rows = await self.db_pool.simple_select_list(
+            table="scheduled_tasks",
+            keyvalues=keyvalues,
+            retcols=(
+                "id",
+                "action",
+                "status",
+                "timestamp",
+                "resource_id",
+                "params",
+                "result",
+                "error",
+            ),
+            desc="get_scheduled_tasks",
+        )
+
+        return [TaskSchedulerWorkerStore._convert_row_to_task(row) for row in rows]
+
+    async def upsert_scheduled_task(self, task: ScheduledTask) -> None:
+        """Upsert a specified `ScheduledTask` in the DB.
+
+        Args:
+            task: the `ScheduledTask` to upsert
+        """
+        await self.db_pool.simple_upsert(
+            "scheduled_tasks",
+            {"id": task.id},
+            {
+                "action": task.action,
+                "status": task.status,
+                "timestamp": task.timestamp,
+                "resource_id": task.resource_id,
+                "params": None if task.params is None else json.dumps(task.params),
+                "result": None if task.result is None else json.dumps(task.result),
+                "error": task.error,
+            },
+            desc="upsert_scheduled_task",
+        )
+
+    async def update_scheduled_task(
+        self,
+        id: str,
+        *,
+        timestamp: Optional[int] = None,
+        status: Optional[TaskStatus] = None,
+        result: Optional[JsonMapping] = None,
+        error: Optional[str] = None,
+    ) -> None:
+        """Update a scheduled task in the DB with some new value(s).
+
+        Args:
+            id: id of the `ScheduledTask` to update
+            timestamp: new timestamp of the task
+            status: new status of the task
+            result: new result of the task
+            error: new error of the task
+        """
+        updatevalues: JsonDict = {}
+        if timestamp is not None:
+            updatevalues["timestamp"] = timestamp
+        if status is not None:
+            updatevalues["status"] = status
+        if result is not None:
+            updatevalues["result"] = json.dumps(result)
+        if error is not None:
+            updatevalues["error"] = error
+        await self.db_pool.simple_update(
+            "scheduled_tasks",
+            {"id": id},
+            updatevalues,
+            desc="update_scheduled_task",
+        )
+
+    async def get_scheduled_task(self, id: str) -> Optional[ScheduledTask]:
+        """Get a specific `ScheduledTask` from its id.
+
+        Args:
+            id: the id of the task to retrieve
+
+        Returns: the task if available, `None` otherwise
+        """
+        row = await self.db_pool.simple_select_one(
+            table="scheduled_tasks",
+            keyvalues={"id": id},
+            retcols=(
+                "id",
+                "action",
+                "status",
+                "timestamp",
+                "resource_id",
+                "params",
+                "result",
+                "error",
+            ),
+            allow_none=True,
+            desc="get_scheduled_task",
+        )
+
+        return TaskSchedulerWorkerStore._convert_row_to_task(row) if row else None
+
+    async def delete_scheduled_task(self, id: str) -> None:
+        """Delete a specific task from its id.
+
+        Args:
+            id: the id of the task to delete
+        """
+        await self.db_pool.simple_delete(
+            "scheduled_tasks",
+            keyvalues={"id": id},
+            desc="delete_scheduled_task",
+        )

synapse/storage/schema/main/delta/79/03_scheduled_tasks.sql

@@ -0,0 +1,26 @@
+/* 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.
+ */
+
+-- cf ScheduledTask docstring for the meaning of the fields.
+CREATE TABLE IF NOT EXISTS scheduled_tasks(
+    id text PRIMARY KEY,
+    action text NOT NULL,
+    status text NOT NULL,
+    timestamp bigint NOT NULL,
+    resource_id text,
+    params text,
+    result text,
+    error text
+);

synapse/types/__init__.py

@@ -15,6 +15,7 @@
 import abc
 import re
 import string
+from enum import Enum
 from typing import (
     TYPE_CHECKING,
     AbstractSet,
@@ -979,3 +980,40 @@ class UserProfile(TypedDict):
 class RetentionPolicy:
     min_lifetime: Optional[int] = None
     max_lifetime: Optional[int] = None
+
+
+class TaskStatus(str, Enum):
+    """Status of a scheduled task"""
+
+    # Task is scheduled but not active
+    SCHEDULED = "scheduled"
+    # Task is active and probably running, and if not
+    # will be run on next scheduler loop run
+    ACTIVE = "active"
+    # Task has completed successfully
+    COMPLETE = "complete"
+    # Task is over and either returned a failed status, or had an exception
+    FAILED = "failed"
+
+
+@attr.s(auto_attribs=True, frozen=True, slots=True)
+class ScheduledTask:
+    """Description of a scheduled task"""
+
+    # id used to identify the task
+    id: str
+    # name of the action to be run by this task
+    action: str
+    # current status of this task
+    status: TaskStatus
+    # if the status is SCHEDULED then this represents when it should be launched,
+    # otherwise it represents the last time this task got a change of state
+    timestamp: int
+    # Optionally bind a task to some resource id for easy retrieval
+    resource_id: Optional[str]
+    # Optional parameters that will be passed to the function ran by the task
+    params: Optional[JsonMapping]
+    # Optional result that can be updated by the running task
+    result: Optional[JsonMapping]
+    # Optional error that should be assigned a value when the status is FAILED
+    error: Optional[str]

synapse/util/task_scheduler.py

@@ -0,0 +1,244 @@
+# 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.
+
+import logging
+from typing import TYPE_CHECKING, Awaitable, Callable, Dict, List, Optional, Set, Tuple
+
+from twisted.python.failure import Failure
+
+from synapse.metrics.background_process_metrics import run_as_background_process
+from synapse.types import JsonMapping, ScheduledTask, TaskStatus
+from synapse.util.stringutils import random_string
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+logger = logging.getLogger(__name__)
+
+
+class TaskScheduler:
+    # Precision of the scheduler, evaluation of tasks to run will only happen
+    # every `SCHEDULE_INTERVAL_MS` ms
+    SCHEDULE_INTERVAL_MS = 5 * 60 * 1000  # 5mn
+    # Time before a complete or failed task is deleted from the DB
+    KEEP_TASKS_FOR_MS = 7 * 24 * 60 * 60 * 1000  # 1 week
+
+    def __init__(self, hs: "HomeServer"):
+        self.store = hs.get_datastores().main
+        self.clock = hs.get_clock()
+        self.running_tasks: Set[str] = set()
+        self.actions: Dict[
+            str,
+            Callable[
+                [ScheduledTask, bool],
+                Awaitable[Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]],
+            ],
+        ] = {}
+        self.run_background_tasks = hs.config.worker.run_background_tasks
+
+        if self.run_background_tasks:
+            self.clock.looping_call(
+                run_as_background_process,
+                TaskScheduler.SCHEDULE_INTERVAL_MS,
+                "scheduled_tasks_loop",
+                self._scheduled_tasks_loop,
+            )
+
+    def register_action(
+        self,
+        function: Callable[
+            [ScheduledTask, bool],
+            Awaitable[Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]],
+        ],
+        action_name: str,
+    ) -> None:
+        """Register a function to be executed when an action is scheduled with
+        the specified action name.
+
+        Actions need to be registered as early as possible so that a resumed action
+        can find its matching function. It's usually better to NOT do that right before
+        calling `schedule_task` but rather in an `__init__` method.
+
+        Args:
+            function: The function to be executed for this action. The parameters
+            passed to the function when launched are the `ScheduledTask` being run,
+            and a `first_launch` boolean to signal if it's a resumed task or the first
+            launch of it. The function should return a tuple of new `status`, `result`
+            and `error` as specified in `ScheduledTask`.
+            action_name: The name of the action to be associated with the function
+        """
+        self.actions[action_name] = function
+
+    async def schedule_task(
+        self,
+        action: str,
+        *,
+        resource_id: Optional[str] = None,
+        timestamp: Optional[int] = None,
+        params: Optional[JsonMapping] = None,
+    ) -> str:
+        """Schedule a new potentially resumable task. A function matching the specified
+        `action` should have been previously registered with `register_action`.
+
+        Args:
+            action: the name of a previously registered action
+            resource_id: a task can be associated with a resource id to facilitate
+                getting all tasks associated with a specific resource
+            timestamp: if `None`, the task will be launched immediately, otherwise it
+                will be launch after the `timestamp` value. Note that this scheduler
+                is not meant to be precise, and the scheduling could be delayed if
+                too many tasks are already running
+            params: a set of parameters that can be easily accessed from inside the
+                executed function
+
+        Returns: the id of the scheduled task
+        """
+        if action not in self.actions:
+            raise Exception(
+                f"No function associated with the action {action} of the scheduled task"
+            )
+
+        launch_now = False
+        if timestamp is None or timestamp < self.clock.time_msec():
+            timestamp = self.clock.time_msec()
+            launch_now = True
+
+        task = ScheduledTask(
+            random_string(16),
+            action,
+            TaskStatus.SCHEDULED,
+            timestamp,
+            resource_id,
+            params,
+            None,
+            None,
+        )
+        await self.store.upsert_scheduled_task(task)
+
+        if launch_now and self.run_background_tasks:
+            await self._launch_task(task, True)
+
+        return task.id
+
+    async def update_task(
+        self,
+        id: str,
+        *,
+        status: Optional[TaskStatus] = None,
+        result: Optional[JsonMapping] = None,
+        error: Optional[str] = None,
+    ) -> None:
+        """Update some task associated values.
+
+        This is used internally, and also exposed publically so it can be used inside task functions.
+        This allows to store in DB the progress of a task so it can be resumed properly after a restart of synapse.
+
+        Args:
+            id: the id of the task to update
+            status: the new `TaskStatus` of the task
+            result: the new result of the task
+            error: the new error of the task
+        """
+        await self.store.update_scheduled_task(
+            id,
+            timestamp=self.clock.time_msec(),
+            status=status,
+            result=result,
+            error=error,
+        )
+
+    async def get_task(self, id: str) -> Optional[ScheduledTask]:
+        """Get a specific task description by id.
+
+        Args:
+            id: the id of the task to retrieve
+
+        Returns: the task description or `None` if it doesn't exist
+            or it has already been cleaned
+        """
+        return await self.store.get_scheduled_task(id)
+
+    async def get_tasks(
+        self, action: str, resource_id: Optional[str]
+    ) -> List[ScheduledTask]:
+        """Get a list of tasks associated with an action name, and
+        optionally with a resource id.
+
+        Args:
+            action: the action name of the tasks to retrieve
+            resource_id: if `None`, returns all associated tasks for
+                the specified action name, regardless of the resource id
+
+        Returns: a list of `ScheduledTask`
+        """
+        return await self.store.get_scheduled_tasks(action, resource_id)
+
+    async def _scheduled_tasks_loop(self) -> None:
+        """Main loop taking care of launching the scheduled tasks when needed."""
+        for task in await self.store.get_scheduled_tasks():
+            if task.id not in self.running_tasks:
+                if (
+                    task.status == TaskStatus.SCHEDULED
+                    and task.timestamp < self.clock.time_msec()
+                ):
+                    await self._launch_task(task, True)
+                elif task.status == TaskStatus.ACTIVE:
+                    await self._launch_task(task, False)
+                elif (
+                    task.status == TaskStatus.COMPLETE
+                    or task.status == TaskStatus.FAILED
+                ) and self.clock.time_msec() > task.timestamp + TaskScheduler.KEEP_TASKS_FOR_MS:
+                    await self.store.delete_scheduled_task(task.id)
+
+    async def _launch_task(self, task: ScheduledTask, first_launch: bool) -> None:
+        """Launch a scheduled task now.
+
+        Args:
+            task: the task to launch
+            first_launch: `True` if it's the first time is launched, `False` otherwise
+        """
+        if task.action not in self.actions:
+            raise Exception(
+                f"No function associated with the action {task.action} of the scheduled task"
+            )
+
+        function = self.actions[task.action]
+
+        async def wrapper() -> None:
+            try:
+                (status, result, error) = await function(task, first_launch)
+            except Exception:
+                f = Failure()
+                logger.error(
+                    f"scheduled task {task.id} failed",
+                    exc_info=(f.type, f.value, f.getTracebackObject()),
+                )
+                status = TaskStatus.FAILED
+                result = None
+                error = f.getErrorMessage()
+
+            await self.update_task(
+                task.id,
+                status=status,
+                result=result,
+                error=error,
+            )
+            self.running_tasks.remove(task.id)
+
+        await self.update_task(task.id, status=TaskStatus.ACTIVE)
+        self.running_tasks.add(task.id)
+        description = task.action
+        if task.resource_id:
+            description += f"-{task.resource_id}"
+        run_as_background_process(description, wrapper)

tests/util/test_task_scheduler.py

@@ -0,0 +1,132 @@
+# 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._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() + 2 * 60 * 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 2mn after now the task should been executed
+        # after the first scheduling loop is run
+        self.reactor.advance((TaskScheduler.SCHEDULE_INTERVAL_MS / 1000) + 1)
+
+        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)
+
+    def test_schedule_task_now(self) -> None:
+        """Schedule a task now and check it runs fine to completion."""
+        task_id = self.get_success(
+            self.task_scheduler.schedule_task("_test_task", params={"val": 1})
+        )
+
+        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("val") == 1)
+
+    async def _raising_task(
+        self, task: ScheduledTask, first_launch: bool
+    ) -> Tuple[TaskStatus, Optional[JsonMapping], Optional[str]]:
+        raise Exception("raising")
+
+    def test_schedule_raising_task_now(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"))
+
+        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, None)
+            # This should never been called
+            return TaskStatus.ACTIVE, None, None
+
+    def test_schedule_resumable_task_now(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"))
+
+        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) + 1)
+
+        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"))