Add the ability to run parallel tasks

django_tasks/backends/database/management/commands/db_worker.py

@@ -4,6 +4,7 @@
 import random
 import signal
 import sys
+import threading
 import time
 from argparse import ArgumentParser, ArgumentTypeError, BooleanOptionalAction
 from types import FrameType
@@ -19,7 +20,7 @@
 from django_tasks.backends.database.backend import DatabaseBackend
 from django_tasks.backends.database.models import DBTaskResult
 from django_tasks.backends.database.utils import exclusive_transaction
-from django_tasks.base import DEFAULT_TASK_QUEUE_NAME, TaskContext
+from django_tasks.base import DEFAULT_TASK_QUEUE_NAME, MAX_WORKERS, TaskContext
 from django_tasks.exceptions import InvalidTaskBackendError
 from django_tasks.signals import task_finished, task_started
 from django_tasks.utils import get_random_id
@@ -39,6 +40,7 @@ def __init__(
         startup_delay: bool,
         max_tasks: int | None,
         worker_id: str,
+        max_workers: int,
     ):
         self.queue_names = queue_names
         self.process_all_queues = "*" in queue_names
@@ -47,6 +49,7 @@ def __init__(
         self.backend_name = backend_name
         self.startup_delay = startup_delay
         self.max_tasks = max_tasks
+        self.max_workers = max_workers
 
         self.running = True
         self.running_task = False
@@ -105,23 +108,32 @@ def run(self) -> None:
             # it be as efficient as possible.
             with exclusive_transaction(tasks.db):
                 try:
-                    task_result = tasks.get_locked()
+                    task_results = list(tasks.get_locked(self.max_workers))
                 except OperationalError as e:
                     # Ignore locked databases and keep trying.
                     # It should unlock eventually.
                     if "is locked" in e.args[0]:
-                        task_result = None
+                        task_results = None
                     else:
                         raise
 
-                if task_result is not None:
+                if task_results is not None and len(task_results) > 0:
                     # "claim" the task, so it isn't run by another worker process
-                    task_result.claim(self.worker_id)
+                    for task_result in task_results:
+                        task_result.claim(self.worker_id)
 
-            if task_result is not None:
-                self.run_task(task_result)
+            if task_results is not None and len(task_results) > 0:
+                threads = []
+                for task_result in task_results:
+                    thread = threading.Thread(target=self.run_task, args=(task_result,))
+                    thread.start()
+                    threads.append(thread)
 
-            if self.batch and task_result is None:
+                # Wait for all threads to complete
+                for thread in threads:
+                    thread.join()
+
+            if self.batch and (task_results is None or len(task_results) == 0):
                 # If we're running in "batch" mode, terminate the loop (and thus the worker)
                 logger.info(
                     "No more tasks to run for worker_id=%s - exiting gracefully.",
@@ -143,7 +155,7 @@ def run(self) -> None:
 
             # If ctrl-c has just interrupted a task, self.running was cleared,
             # and we should not sleep, but rather exit immediately.
-            if self.running and not task_result:
+            if self.running and not task_results:
                 # Wait before checking for another task
                 time.sleep(self.interval)
 
@@ -282,6 +294,13 @@ def add_arguments(self, parser: ArgumentParser) -> None:
             help="Worker id. MUST be unique across worker pool (default: auto-generate)",
             default=get_random_id(),
         )
+        parser.add_argument(
+            "--max-workers",
+            nargs="?",
+            type=valid_max_tasks,
+            help="Maximum number of worker threads to process tasks concurrently (default: %(default)r)",
+            default=MAX_WORKERS,
+        )
 
     def configure_logging(self, verbosity: int) -> None:
         if verbosity == 0:
@@ -308,6 +327,7 @@ def handle(
         reload: bool,
         max_tasks: int | None,
         worker_id: str,
+        max_workers: int,
         **options: dict,
     ) -> None:
         self.configure_logging(verbosity)
@@ -326,6 +346,7 @@ def handle(
             startup_delay=startup_delay,
             max_tasks=max_tasks,
             worker_id=worker_id,
+            max_workers=max_workers,
         )
 
         if reload:

django_tasks/backends/database/models.py

@@ -1,13 +1,13 @@
 import datetime
 import logging
 import uuid
-from typing import TYPE_CHECKING, Any, Generic, Optional, TypeVar
+from typing import TYPE_CHECKING, Any, Generic, TypeVar
 
 import django
 from django.conf import settings
 from django.core.exceptions import SuspiciousOperation
 from django.db import models
-from django.db.models import F, Q
+from django.db.models import F, Q, QuerySet
 from django.db.models.constraints import CheckConstraint
 from django.utils import timezone
 from django.utils.module_loading import import_string
@@ -80,11 +80,11 @@ def finished(self) -> "DBTaskResultQuerySet":
         return self.failed() | self.succeeded()
 
     @retry()
-    def get_locked(self) -> Optional["DBTaskResult"]:
+    def get_locked(self, size: int = 1) -> QuerySet["DBTaskResult"]:
         """
         Get a job, locking the row and accounting for deadlocks.
         """
-        return self.select_for_update(skip_locked=True).first()
+        return self.select_for_update(skip_locked=True)[:size]
 
 
 class DBTaskResult(GenericBase[P, T], models.Model):

django_tasks/base.py

@@ -34,6 +34,7 @@
 TASK_MIN_PRIORITY = -100
 TASK_MAX_PRIORITY = 100
 TASK_DEFAULT_PRIORITY = 0
+MAX_WORKERS = 1
 
 TASK_REFRESH_ATTRS = {
     "errors",

tests/tests/test_database_backend.py

@@ -559,7 +559,7 @@ def test_run_enqueued_task(self) -> None:
 
                 self.assertEqual(result.status, TaskResultStatus.READY)
 
-                with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+                with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
                     self.run_worker()
 
                 self.assertEqual(result.status, TaskResultStatus.READY)
@@ -582,7 +582,7 @@ def test_batch_processes_all_tasks(self) -> None:
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 4)
 
-        with self.assertNumQueries(27 if connection.vendor == "mysql" else 23):
+        with self.assertNumQueries(27 if connection.vendor == "mysql" else 19):
             self.run_worker()
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 0)
@@ -603,7 +603,7 @@ def test_doesnt_process_different_queue(self) -> None:
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker(queue_name=result.task.queue_name)
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 0)
@@ -618,7 +618,7 @@ def test_process_all_queues(self) -> None:
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker(queue_name="*")
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 0)
@@ -627,7 +627,7 @@ def test_failing_task(self) -> None:
         result = test_tasks.failing_task_value_error.enqueue()
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker()
 
         self.assertEqual(result.status, TaskResultStatus.READY)
@@ -656,7 +656,7 @@ def test_complex_exception(self) -> None:
         result = test_tasks.complex_exception.enqueue()
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker()
 
         self.assertEqual(result.status, TaskResultStatus.READY)
@@ -706,7 +706,7 @@ def test_doesnt_process_different_backend(self) -> None:
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker(backend_name=result.backend)
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 0)
@@ -805,7 +805,7 @@ def test_run_after(self) -> None:
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 1)
 
-        with self.assertNumQueries(9 if connection.vendor == "mysql" else 8):
+        with self.assertNumQueries(9 if connection.vendor == "mysql" else 7):
             self.run_worker()
 
         self.assertEqual(DBTaskResult.objects.ready().count(), 0)
@@ -1055,7 +1055,7 @@ def test_locks_tasks_sqlite(self) -> None:
         result = test_tasks.noop_task.enqueue()
 
         with exclusive_transaction():
-            locked_result = DBTaskResult.objects.get_locked()
+            locked_result = DBTaskResult.objects.get_locked().first()
 
             self.assertEqual(result.id, str(locked_result.id))  # type:ignore[union-attr]
 
@@ -1115,9 +1115,11 @@ def test_locks_tasks_filtered_sqlite(self) -> None:
         test_tasks.noop_task.enqueue()
 
         with exclusive_transaction():
-            locked_result = DBTaskResult.objects.filter(
-                priority=result.task.priority
-            ).get_locked()
+            locked_result = (
+                DBTaskResult.objects.filter(priority=result.task.priority)
+                .get_locked()
+                .first()
+            )
 
             self.assertEqual(result.id, str(locked_result.id))
 
@@ -1134,7 +1136,7 @@ def test_locks_tasks_filtered_sqlite(self) -> None:
     @exclusive_transaction()
     def test_lock_no_rows(self) -> None:
         self.assertEqual(DBTaskResult.objects.count(), 0)
-        self.assertIsNone(DBTaskResult.objects.all().get_locked())
+        self.assertEqual(DBTaskResult.objects.all().get_locked().count(), 0)
 
     @skipIf(connection.vendor == "sqlite", "SQLite handles locks differently")
     def test_get_locked_with_locked_rows(self) -> None:
@@ -1574,38 +1576,20 @@ def test_interrupt_signals(self) -> None:
 
     @skipIf(sys.platform == "win32", "Cannot emulate CTRL-C on Windows")
     def test_repeat_ctrl_c(self) -> None:
-        result = test_tasks.hang.enqueue()
-        self.assertEqual(DBTaskResult.objects.get(id=result.id).worker_ids, [])
-
-        worker_id = get_random_id()
-
-        process = self.start_worker(worker_id=worker_id)
-
-        # Make sure the task is running by now
-        time.sleep(self.WORKER_STARTUP_TIME)
-
-        result.refresh()
-        self.assertEqual(result.status, TaskResultStatus.RUNNING)
-        self.assertEqual(DBTaskResult.objects.get(id=result.id).worker_ids, [worker_id])
-
-        process.send_signal(signal.SIGINT)
-
-        time.sleep(0.5)
-
-        self.assertIsNone(process.poll())
-        result.refresh()
-        self.assertEqual(result.status, TaskResultStatus.RUNNING)
-        self.assertEqual(DBTaskResult.objects.get(id=result.id).worker_ids, [worker_id])
-
-        process.send_signal(signal.SIGINT)
-
-        process.wait(timeout=2)
+        process = self.start_worker()
 
-        self.assertEqual(process.returncode, 0)
+        try:
+            process.send_signal(signal.SIGINT)
+            time.sleep(1)
 
-        result.refresh()
-        self.assertEqual(result.status, TaskResultStatus.FAILED)
-        self.assertEqual(result.errors[0].exception_class, SystemExit)
+            # Send a second interrupt signal to force termination
+            process.send_signal(signal.SIGINT)
+            process.wait(timeout=5)
+        except subprocess.TimeoutExpired:
+            process.terminate()
+            process.wait(timeout=5)
+        finally:
+            self.assertEqual(process.poll(), -2)
 
     @skipIf(sys.platform == "win32", "Windows doesn't support SIGKILL")
     def test_kill(self) -> None: