From c7d1e5d0693b78663f3160abc33d52a975173f72 Mon Sep 17 00:00:00 2001
From: Raphael Michel <michel@rami.io>
Date: Wed, 19 Aug 2020 11:29:53 +0200
Subject: [PATCH] Allow to reduce the interval of some cronjobs (#1753)

---
 src/pretix/api/signals.py          |  3 ++
 src/pretix/base/services/orders.py |  2 +
 src/pretix/base/services/quotas.py |  2 +
 src/pretix/helpers/periodic.py     | 61 ++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+)
 create mode 100644 src/pretix/helpers/periodic.py

diff --git a/src/pretix/api/signals.py b/src/pretix/api/signals.py
index 689cde048..b7c33909c 100644
--- a/src/pretix/api/signals.py
+++ b/src/pretix/api/signals.py
@@ -6,6 +6,7 @@ from django_scopes import scopes_disabled
 
 from pretix.api.models import ApiCall, WebHookCall
 from pretix.base.signals import periodic_task
+from pretix.helpers.periodic import minimum_interval
 
 register_webhook_events = Signal(
     providing_args=[]
@@ -19,11 +20,13 @@ instances.
 
 @receiver(periodic_task)
 @scopes_disabled()
+@minimum_interval(minutes_after_success=12 * 60)
 def cleanup_webhook_logs(sender, **kwargs):
     WebHookCall.objects.filter(datetime__lte=now() - timedelta(days=30)).delete()
 
 
 @receiver(periodic_task)
 @scopes_disabled()
+@minimum_interval(minutes_after_success=12 * 60)
 def cleanup_api_logs(sender, **kwargs):
     ApiCall.objects.filter(created__lte=now() - timedelta(hours=24)).delete()
diff --git a/src/pretix/base/services/orders.py b/src/pretix/base/services/orders.py
index 91fd9a102..7763d914e 100644
--- a/src/pretix/base/services/orders.py
+++ b/src/pretix/base/services/orders.py
@@ -53,6 +53,7 @@ from pretix.base.signals import (
 )
 from pretix.celery_app import app
 from pretix.helpers.models import modelcopy
+from pretix.helpers.periodic import minimum_interval
 
 error_messages = {
     'unavailable': _('Some of the products you selected were no longer available. '
@@ -988,6 +989,7 @@ def expire_orders(sender, **kwargs):
 
 @receiver(signal=periodic_task)
 @scopes_disabled()
+@minimum_interval(minutes_after_success=60)
 def send_expiry_warnings(sender, **kwargs):
     today = now().replace(hour=0, minute=0, second=0)
     days = None
diff --git a/src/pretix/base/services/quotas.py b/src/pretix/base/services/quotas.py
index 9dd78231d..110ddcdf9 100644
--- a/src/pretix/base/services/quotas.py
+++ b/src/pretix/base/services/quotas.py
@@ -18,6 +18,7 @@ from pretix.base.models import (
 )
 from pretix.celery_app import app
 
+from ...helpers.periodic import minimum_interval
 from ..signals import periodic_task, quota_availability
 
 
@@ -403,6 +404,7 @@ class QuotaAvailability:
 
 
 @receiver(signal=periodic_task)
+@minimum_interval(minutes_after_success=60)
 def build_all_quota_caches(sender, **kwargs):
     refresh_quota_caches.apply_async()
 
diff --git a/src/pretix/helpers/periodic.py b/src/pretix/helpers/periodic.py
new file mode 100644
index 000000000..6263e086e
--- /dev/null
+++ b/src/pretix/helpers/periodic.py
@@ -0,0 +1,61 @@
+import logging
+import uuid
+from functools import wraps
+
+from django.core.cache import cache
+
+logger = logging.getLogger(__name__)
+
+
+def minimum_interval(minutes_after_success, minutes_after_error=0, minutes_running_timeout=30):
+    """
+    This is intended to be used as a decorator on receivers of the ``periodic_task`` signal.
+    It stores the result in the task in the cache (usually redis) to ensure the receiver function
+    isn't executed less than ``minutes_after_success`` after the last successful run and no less
+    than ``minutes_after_error`` after the last failed run. There's also a simple locking mechanism
+    implemented making sure the function is not called a second time while it is running, unless
+    ``minutes_running_timeout`` have passed. This locking mechanism is naive and not safe of
+    race-conditions, it should not be relied upon.
+    """
+    def deco(f):
+        @wraps(f)
+        def wrapper(*args, **kwargs):
+            key_running = f'pretix_periodic_{f.__module__}.{f.__name__}_running'
+            key_result = f'pretix_periodic_{f.__module__}.{f.__name__}_result'
+
+            running_val = cache.get(key_running)
+            if running_val:
+                # Currently running
+                return
+
+            result_val = cache.get(key_result)
+            if result_val:
+                # Has run recently
+                return
+
+            uniqid = str(uuid.uuid4())
+            cache.set(key_running, uniqid, timeout=minutes_running_timeout * 60)
+            try:
+                retval = f(*args, **kwargs)
+            except Exception as e:
+                try:
+                    cache.set(key_result, 'error', timeout=minutes_after_error * 60)
+                except:
+                    logger.exception('Could not store result')
+                raise e
+            else:
+                try:
+                    cache.set(key_result, 'success', timeout=minutes_after_success * 60)
+                except:
+                    logger.exception('Could not store result')
+                return retval
+            finally:
+                try:
+                    if cache.get(key_running) == uniqid:
+                        cache.delete(key_running)
+                except:
+                    logger.exception('Could not release lock')
+
+        return wrapper
+
+    return deco