Prizetap: drawing the raffle automatically

brightIDfaucet/celery.py

@@ -45,6 +45,10 @@
     'update-donation-receipt-status': {
         "task": "faucet.tasks.update_donation_receipt_pending_status",
         "schedule": 60,
+    },
+    "draw-prizetap-raffles": {
+        "task": "prizetap.tasks.draw_the_expired_raffles",
+        "schedule": 60
     }
 }
 

core/helpers.py

@@ -0,0 +1,20 @@
+import time
+from contextlib import contextmanager
+from django.core.cache import cache
+
+@contextmanager
+def memcache_lock(lock_id, oid, lock_expire=60):
+    timeout_at = time.monotonic() + lock_expire
+    # cache.add fails if the key already exists
+    status = cache.add(lock_id, oid, lock_expire)
+    try:
+        yield status
+    finally:
+        # memcache delete is very slow, but we have to use it to take
+        # advantage of using add() for atomic locking
+        if time.monotonic() < timeout_at and status:
+            # don't release the lock if we exceeded the timeout
+            # to lessen the chance of releasing an expired lock
+            # owned by someone else
+            # also don't release the lock if we didn't acquire it
+            cache.delete(lock_id)

prizetap/tasks.py

@@ -0,0 +1,30 @@
+from celery import shared_task
+from django.utils import timezone
+from core.helpers import memcache_lock
+from .models import Raffle
+from .utils import PrizetapContractClient
+
+
+@shared_task(bind=True)
+def draw_the_expired_raffles(self):
+
+    id = f"{self.name}-LOCK"
+
+    with memcache_lock(id, self.app.oid) as acquired:
+        if not acquired:
+            print(f"Could not acquire process lock at {self.name}")
+            return
+
+        raffles_queryset = (
+            Raffle.objects
+            .filter(deadline__lt=timezone.now())
+            .filter(is_active=True)
+        )
+        if raffles_queryset.count() > 0:
+            for raffle in raffles_queryset:
+                if raffle.number_of_onchain_entries > 0 and not raffle.winner_entry:
+                    print(f"Drawing the raffle {raffle.name}")
+                    raffle_client = PrizetapContractClient(raffle)
+                    if raffle_client.draw_raffle():
+                        raffle.is_active = False
+                        raffle.save()