| # DIST1: Message Queue — Race Condition Repair |
|
|
| ## Goal |
| Fix 3 race conditions in the message queue that cause message loss, duplication, |
| and crashes under concurrent load. |
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|
| ## Requirements |
| 1. `put()` must atomically check capacity AND add the message (no TOCTOU race) |
| 2. `get()` must use an acknowledgment pattern — messages must not be removed until |
| the consumer explicitly acknowledges successful processing |
| 3. The priority queue must use a deterministic, type-safe tie-breaker for equal-priority |
| messages (comparing message payloads is not safe — payloads can be any type) |
| 4. All tests must pass: `pytest tests/` |
| 5. The queue must handle 10,000 messages across 20 concurrent threads with zero loss |
|
|
| ## Supporting Documents |
| - `mqueue/queue.py` — Main queue implementation (bugs 1 and 2) |
| - `mqueue/priority.py` — Priority queue comparator (bug 3) |
| - `mqueue/consumer.py` — Consumer interface (needs ack/nack support) |
| - `tests/test_concurrent.py` — Concurrent correctness tests (fail with bugs) |
| - `tests/test_message_loss.py` — Zero-loss guarantee test |
|
|
| ## Important |
| The single-threaded tests (`test_single_thread.py`) pass even with the bugs. |
| The concurrent tests expose the race conditions. The acknowledgment pattern means |
| `get()` should return a message AND a receipt/token, and the message is only |
| confirmed-delivered when `ack(receipt)` is called. |
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