Smaller locking window for the background processor (#183)

spiffworkflow-backend/src/spiffworkflow_backend/services/process_instance_queue_service.py

@@ -1,5 +1,6 @@
 import time
 from typing import List
+from typing import Optional
 
 from flask import current_app
 
@@ -84,8 +85,33 @@ class ProcessInstanceQueueService:
 
         ProcessInstanceLockService.lock(process_instance.id, queue_entry)
 
-    @staticmethod
+    @classmethod
+    def entries_with_status(
+        cls,
+        status_value: str = ProcessInstanceStatus.waiting.value,
+        locked_by: Optional[str] = None,
+    ) -> List[ProcessInstanceQueueModel]:
+        return (
+            db.session.query(ProcessInstanceQueueModel)
+            .filter(
+                ProcessInstanceQueueModel.status == status_value,
+                ProcessInstanceQueueModel.locked_by == locked_by,
+            )
+            .all()
+        )
+
+    @classmethod
+    def peek_many(
+        cls,
+        status_value: str = ProcessInstanceStatus.waiting.value,
+    ) -> List[int]:
+        queue_entries = cls.entries_with_status(status_value, None)
+        ids_with_status = [entry.process_instance_id for entry in queue_entries]
+        return ids_with_status
+
+    @classmethod
     def dequeue_many(
+        cls,
         status_value: str = ProcessInstanceStatus.waiting.value,
     ) -> List[int]:
         locked_by = ProcessInstanceLockService.locked_by()
@@ -102,14 +128,7 @@ class ProcessInstanceQueueService:
 
         db.session.commit()
 
-        queue_entries = (
+        queue_entries = cls.entries_with_status(status_value, locked_by)
-            db.session.query(ProcessInstanceQueueModel)
-            .filter(
-                ProcessInstanceQueueModel.status == status_value,
-                ProcessInstanceQueueModel.locked_by == locked_by,
-            )
-            .all()
-        )
 
         locked_ids = ProcessInstanceLockService.lock_many(queue_entries)
 

spiffworkflow-backend/src/spiffworkflow_backend/services/process_instance_service.py

@@ -84,15 +84,15 @@ class ProcessInstanceService:
     @staticmethod
     def do_waiting(status_value: str = ProcessInstanceStatus.waiting.value) -> None:
         """Do_waiting."""
-        locked_process_instance_ids = ProcessInstanceQueueService.dequeue_many(
+        process_instance_ids_to_check = ProcessInstanceQueueService.peek_many(
             status_value
         )
-        if len(locked_process_instance_ids) == 0:
+        if len(process_instance_ids_to_check) == 0:
             return
 
         records = (
             db.session.query(ProcessInstanceModel)
-            .filter(ProcessInstanceModel.id.in_(locked_process_instance_ids))  # type: ignore
+            .filter(ProcessInstanceModel.id.in_(process_instance_ids_to_check))  # type: ignore
             .all()
         )
         process_instance_lock_prefix = "Background"