Add a lock to the task assignment

While it shouldn't take very long, this should nonetheless
avoid race conditions on the task assignment logic. Following
the discussion here: https://stackoverflow.com/q/18213619

2 files changed, 14 insertions, 1 deletions

diff --git a/app/utils/tasks.py b/app/utils/tasks.py
index b0f5c27..8356876 100644
--- a/app/utils/tasks.py
+++ b/app/utils/tasks.py
@@ -5,13 +5,26 @@
 """
 
 import random
+import multiprocessing
 
 from flask import current_app
 
 from app.models import Dataset, Task
 
+TASK_LOCK = multiprocessing.Lock()
+
 
 def generate_user_task(user):
+    task = None
+    TASK_LOCK.acquire(timeout=10)
+    try:
+        task = realgenerate_user_task(user)
+    finally:
+        TASK_LOCK.release()
+    return task
+
+
+def realgenerate_user_task(user):
     """
     Generate new task for a given user.
 
diff --git a/boot.sh b/boot.sh
index 93e64d2..c15b1c4 100644
--- a/boot.sh
+++ b/boot.sh
@@ -13,4 +13,4 @@ while true; do
 	sleep 5
 done
 
-exec gunicorn -b :7831 --access-logfile - --error-logfile - annotate_change:app
+exec gunicorn -b :7831 --preload --access-logfile - --error-logfile - annotate_change:app