From ee2856c5fcdb9a720ce62bc58b5e4d3c4d5cb693 Mon Sep 17 00:00:00 2001
From: Kevin Alberts <kevin@kevinalberts.nl>
Date: Wed, 11 Nov 2020 17:18:21 +0100
Subject: [PATCH] Add lock to make sure only one ical_sync can run
 simultaneously

---
 .gitignore                                    |  1 +
 davinci/icalendar/decorators.py               | 61 +++++++++++++++++++
 .../management/commands/ical_sync.py          |  2 +
 requirements.txt                              |  1 +
 4 files changed, 65 insertions(+)
 create mode 100644 davinci/icalendar/decorators.py

diff --git a/.gitignore b/.gitignore
index 75efcf1..0bb3718 100644
--- a/.gitignore
+++ b/.gitignore
@@ -215,6 +215,7 @@ fabric.properties
 .idea/
 
 venv/
+static/
 
 davinci/local.py
 
diff --git a/davinci/icalendar/decorators.py b/davinci/icalendar/decorators.py
new file mode 100644
index 0000000..b9d8c02
--- /dev/null
+++ b/davinci/icalendar/decorators.py
@@ -0,0 +1,61 @@
+import time
+import logging
+
+from lockfile import FileLock, AlreadyLocked, LockTimeout
+from django.conf import settings
+
+# Lock timeout value - how long to wait for the lock to become available.
+# Default behavior is to never wait for the lock to be available (fail fast)
+LOCK_WAIT_TIMEOUT = getattr(settings, "DEFAULT_LOCK_WAIT_TIMEOUT", -1)
+
+
+def handle_lock(handle):
+    """
+    Decorate the handle method with a file lock to ensure there is only ever
+    one process running at any one time.
+    """
+
+    def wrapper(self, *args, **options):
+
+        start_time = time.time()
+        verbosity = options.get('verbosity', 0)
+        if verbosity == 0:
+            level = logging.WARNING
+        elif verbosity == 1:
+            level = logging.INFO
+        else:
+            level = logging.DEBUG
+
+        logging.basicConfig(level=level, format="%(message)s")
+        logging.debug("-" * 72)
+
+        lock_name = self.__module__.split('.').pop()
+        lock = FileLock(lock_name)
+
+        logging.debug("%s - acquiring lock..." % lock_name)
+        try:
+            lock.acquire(LOCK_WAIT_TIMEOUT)
+        except AlreadyLocked:
+            logging.debug("lock already in place. quitting.")
+            return
+        except LockTimeout:
+            logging.debug("waiting for the lock timed out. quitting.")
+            return
+        logging.debug("acquired.")
+
+        try:
+            handle(self, *args, **options)
+        except:
+            import traceback
+            logging.warning("Command Failed")
+            logging.warning('==' * 72)
+            logging.warning(traceback.format_exc())
+            logging.warning('==' * 72)
+
+        logging.debug("releasing lock...")
+        lock.release()
+        logging.debug("released.")
+
+        logging.info("done in %.2f seconds" % (time.time() - start_time))
+
+    return wrapper
diff --git a/davinci/icalendar/management/commands/ical_sync.py b/davinci/icalendar/management/commands/ical_sync.py
index 527bdd1..3f65370 100644
--- a/davinci/icalendar/management/commands/ical_sync.py
+++ b/davinci/icalendar/management/commands/ical_sync.py
@@ -3,12 +3,14 @@ import logging
 from django.core.management.base import BaseCommand
 from django.utils import timezone
 
+from davinci.icalendar.decorators import handle_lock
 from davinci.icalendar.models import ICalSync
 
 
 class Command(BaseCommand):
     help = 'Sychronize iCal syncs that need to be synchronized.'
 
+    @handle_lock
     def handle(self, *args, **options):
         logger = logging.getLogger("davinci.icalendar.ical_sync")
         logger.debug(f"Command `ical_sync` invoked")
diff --git a/requirements.txt b/requirements.txt
index e0e4906..7037f3c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,3 +4,4 @@ django-durationwidget>=1.0.5,<1.1
 humanize>=3.1.0,<3.2
 ics>=0.7,<0.8
 caldav>=0.7.1,<0.8
+lockfile>=0.12.2,<0.13