Yicong-Huang opened a new issue, #4524:
URL: https://github.com/apache/texera/issues/4524
## Summary
`core/runnables/test_main_loop.py::TestMainLoop::test_main_loop_thread_can_align_ecm`
is intermittently red on CI for unrelated PRs (observed on #4512 and #4520,
same assertion at `test_main_loop.py:1176`). Locally it always passes (100/100
with `-x` on macOS, 30/30 of the full file).
## Root cause
The test assumes that two items put into `output_queue` come out in FIFO
order:
```python
input_queue.put(ECMElement(tag=mock_control_input_channel,
payload=test_ecm)) # 1
input_queue.put(mock_binary_data_element)
# 2
input_queue.put(ECMElement(tag=mock_data_input_channel, payload=test_ecm))
# 3 -> aligns ECM, runs NoOperation
output_data_element: DataElement = output_queue.get() # expects data first
...
output_control_element: DCMElement = output_queue.get() # expects control
reply second
```
But `output_queue` is an `InternalQueue`, which is a
`LinkedBlockingMultiQueue` keyed by channel with **priority 1 for control
sub-queues and priority 2 for data sub-queues** (`internal_queue.py:80`).
`LinkedBlockingMultiQueue.get()` always pops the highest-priority enabled
sub-queue first.
In MainLoop the puts happen sequentially:
1. DataElement → data sub-queue (priority 2)
2. NoOperation reply DCMElement → control sub-queue (priority 1)
On a fast machine, the test calls `.get()` after step 1 but before step 2,
so only the data is in the queue — it comes out first, the test passes. On a
slow CI runner, MainLoop reaches step 2 before the test calls `.get()` — both
items are queued, the priority queue returns the control reply first, and the
assertion at line 1176 fails with:
```
AssertionError: ChannelIdentity(..., to='sender', is_control=True) # actual
(control)
!= ChannelIdentity(..., to='dummy_worker_id', is_control=False)
# expected (data)
```
The production behavior is correct — control should win priority over data
on the egress queue.
## Proposed fix
Make the test order-tolerant: drain two items from `output_queue`, identify
each by type (`DataElement` vs `DCMElement`), and assert each independently. No
production code change.
## Priority
P2 – Medium (blocks unrelated PRs every few CI runs)
## Task Type
- [x] Testing / QA
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