implement the queue

src/routes/answers.py

@@ -7,6 +7,8 @@ from utils.observer import SocketObserver, Status, Subject, request2status
 import functools
 import json, uuid
 
+from utils.queue_manager import QueueManager
+
 router = Blueprint('answers', __name__, url_prefix='/answers')
 
 ALLOWED_EXT = {'json'}
@@ -47,6 +49,9 @@ def validate_json_format_for_code_refinement(data: str) -> dict[str, dict[str, s
         raise InvalidJsonFormatError()
 
 
+QUEUE_MANAGER = QueueManager(1)
+
+
 def handler(type_: str, validate_json: Callable, evaluate_submission: Callable):
     file = request.files.get('file')
     if file is None or file.filename is None or file.filename.split('.')[-1] not in ALLOWED_EXT:
@@ -71,7 +76,7 @@ def handler(type_: str, validate_json: Callable, evaluate_submission: Callable):
         obs = SocketObserver(sid, socket_emit)
         subject.registerObserver(obs)
 
-    subject.launch_task(validated)
+    QUEUE_MANAGER.submit(subject, validated)
     url = url_for(f".status", id=process_id, _external=True)
     return jsonify(
         {
@@ -124,6 +129,8 @@ def status(id):
             obs.updatePercentage(subject.percent)
             subject.registerObserver(obs)
         return jsonify({"status": "processing", "percent": subject.percent})
+    elif subject.status == Status.WAITING:
+        return jsonify({"status": "waiting", "queue_position": QUEUE_MANAGER.get_position(id)})
     elif subject.status == Status.CREATED:
         return jsonify({"status": "created"})
 

src/utils/observer.py

@@ -6,6 +6,7 @@ from typing import Callable, Optional, Set, Any
 
 class Status(Enum):
     CREATED = "created"
+    WAITING = "waiting"
     PROCESSING = "processing"
     COMPLETE = "complete"
 
@@ -65,19 +66,5 @@ class Subject:
         self.results = results
         # TODO: maybe save results to disk here?
 
-    def launch_task(self, *args, **kwargs):
-        self.status = Status.PROCESSING
-        t = Thread(
-            target=self.task,
-            args=args,
-            kwargs={
-                **kwargs,
-                "percent_cb": self.notifyPercentage,
-                "complete_cb": self.notifyComplete,
-            },
-            daemon=True,
-        )
-        t.start()
-
 
 request2status: dict[str, Subject] = {}

src/utils/queue_manager.py

@@ -0,0 +1,46 @@
+from concurrent.futures import ThreadPoolExecutor
+from collections import deque
+from utils.observer import Subject, Status
+
+
+class QueueManager:
+    """
+    Manages a queue of Subjects, handling status transitions and allowing position queries:
+      CREATED -> WAITING -> PROCESSING -> COMPLETE
+    """
+
+    def __init__(self, max_workers: int = 5) -> None:
+        self.executor = ThreadPoolExecutor(max_workers=max_workers)
+        self.wait_queue: deque[str] = deque()
+
+    def submit(self, subject: Subject, *args, **kwargs) -> None:
+        subject.status = Status.WAITING
+        # Add to waiting queue
+        self.wait_queue.append(subject.id)
+        # Schedule the task on the executor
+        self.executor.submit(self._run, subject, *args, **kwargs)
+
+    def get_position(self, subject_id: str) -> int:
+        """
+        Returns 1-based position in waiting queue, or 0 if not waiting.
+        """
+        try:
+            # index returns 0-based, so +1
+            return self.wait_queue.index(subject_id) + 1
+        except ValueError:
+            return 0
+
+    def _run(self, subject: Subject, *args, **kwargs) -> None:
+        # Remove from waiting queue as it's now processing
+        try:
+            self.wait_queue.remove(subject.id)
+        except ValueError:
+            pass
+        subject.status = Status.PROCESSING
+        # Execute the user-defined task synchronously in this worker thread
+        subject.task(
+            *args,
+            percent_cb=subject.notifyPercentage,
+            complete_cb=subject.notifyComplete,
+            **kwargs,
+        )