Add method to check for a lock's existance and force it to release if stale.

mayan/apps/lock_manager/managers.py

@@ -49,3 +49,21 @@ class LockManager(models.Manager):
         else:
             logger.debug('acquired lock: %s', name)
             return lock
+
+    def check_existing(self, **kwargs):
+        try:
+            existing_lock = self.get(**kwargs)
+        except self.model.DoesNotExist:
+            return False
+        else:
+            # Lock exists, try to re-acquire it in case it is a stale lock
+            try:
+                lock = self.acquire_lock(existing_lock.name)
+            except LockError:
+                # This is expected, try to acquire it to force it to
+                # timeout in case it is a stale lock.
+                return True
+            else:
+                # Able to re-acquire anothers lock, so we release it now
+                lock.release()
+                return False