Description

When is_restricted_to_select_one_submission is enabled for a challenge phase, multiple submissions can become public simultaneously due to a race condition. This violates the business rule that only one submission should be public at a time.

Location

File: apps/jobs/views.py
Lines:

• 342-349 (in challenge_submission function)
• 475-485 (in change_submission_data_and_visibility function)

Reproduction

1. Save the attached test script as test_bug_race_condition.py
2. Run: python3 test_bug_race_condition.py
3. Observe the output showing 2 public submissions instead of 1

Test Output:
Initial: 1 public submission(s) Final: 2 public submission(s) - IDs: [2, 3]

Expected Behavior

When a challenge phase has is_restricted_to_select_one_submission=True:

• Only 1 submission should be public at any given time
• When making a new submission public, the existing public submission should be made private first
• This should work correctly even with concurrent requests

Actual Behavior

• Multiple submissions can become public simultaneously
• The race condition occurs because there is no database-level locking
• Both concurrent requests pass the count() == 1 check at the same time
• Both proceed to make their submissions public