Coalesce multiple provisioning requests

backend/helpers/threads.py

@@ -21,8 +21,22 @@ def request_provision():
     try:
         provisioning_queue.send("provision", timeout=0)
     except BusyError:
-        # If we can't signal for some reason, silently fail.
+        # If we can't signal for some reason (queue limit reached), silently
+        # fail.
         pass
 
 def wait_provision():
+    # We first wait until there's any message in the queue.
     provisioning_queue.receive()
+    # After that, we check if there are any more messages, to prevent a couple
+    # of (long) provisioning runs to be done back-to-back in case of multiple
+    # provisioning requests. Note however that if a request comes in during the
+    # middle of a provisioning run, we still do another one right after to make
+    # sure we propagate the latest changes right away.
+    try:
+        while True:
+            # We read with zero timeout, so we get an exception right away if
+            # the queue is empty.
+            provisioning_queue.receive(timeout=0)
+    except BusyError:
+        pass