fix(events): keep registration status reads nonblocking

apps/events/tests/integration/test_checkout_lock_contention.py

@@ -0,0 +1,78 @@
+"""PostgreSQL contention checks for the checkout expiry worker and status API."""
+
+import threading
+import time
+from datetime import timedelta
+
+import pytest
+from django.db import connection, connections, transaction
+from django.test import Client
+from django.utils import timezone
+
+from apps.events.checkout import expire_stale_registration_checkouts
+from apps.events.models import Event, Registration
+from apps.users.models import User
+from core.authentication import create_jwt_token
+
+
+@pytest.mark.django_db(transaction=True)
+@pytest.mark.integration
+def test_status_reads_and_expiry_worker_progress_around_a_locked_checkout():
+    if connection.vendor != "postgresql":
+        pytest.skip("PostgreSQL row locks are required")
+
+    now = timezone.now()
+    event = Event.objects.create(
+        title="Checkout lock test", slug="checkout-lock-test", description="Lock test",
+        start_time=now + timedelta(days=2), end_time=now + timedelta(days=2, hours=1),
+        registration_start_date=now - timedelta(days=1),
+        registration_end_date=now + timedelta(days=1),
+        status=Event.StatusChoices.PUBLISHED, price=1000, capacity=2,
+    )
+    user = User.objects.create_user(username="checkout-lock-owner", mobile="09191112233", password="TestPass123!")
+    other = User.objects.create_user(username="checkout-lock-other", mobile="09191112234", password="TestPass123!")
+    locked = Registration.objects.create(
+        event=event, user=user, status=Registration.StatusChoices.PENDING,
+        checkout_expires_at=now - timedelta(minutes=2),
+    )
+    free = Registration.objects.create(
+        event=event, user=other, status=Registration.StatusChoices.PENDING,
+        checkout_expires_at=now - timedelta(minutes=1),
+    )
+    acquired = threading.Event()
+    release = threading.Event()
+
+    def hold_row_lock():
+        try:
+            with transaction.atomic():
+                Registration.objects.select_for_update().get(pk=locked.pk)
+                acquired.set()
+                release.wait(10)
+        finally:
+            connections.close_all()
+
+    holder = threading.Thread(target=hold_row_lock)
+    holder.start()
+    try:
+        assert acquired.wait(5)
+        start = time.monotonic()
+        response = Client().get(
+            f"/api/events/{event.slug}/registration/status",
+            HTTP_AUTHORIZATION=f"Bearer {create_jwt_token(user)}",
+        )
+        assert response.status_code == 200
+        assert time.monotonic() - start < 2
+
+        assert expire_stale_registration_checkouts(event_id=event.id) == 1
+        locked.refresh_from_db()
+        free.refresh_from_db()
+        assert locked.status == Registration.StatusChoices.PENDING
+        assert free.status == Registration.StatusChoices.CANCELLED
+    finally:
+        release.set()
+        holder.join(timeout=5)
+
+    assert not holder.is_alive()
+    assert expire_stale_registration_checkouts(event_id=event.id) == 1
+    locked.refresh_from_db()
+    assert locked.status == Registration.StatusChoices.CANCELLED