Memory safety does not prevent deadlock
Mutex guards protect data races, but two threads can still wait forever when they acquire the same locks in opposite order. A stable global order removes the circular-wait condition for this lock set.
rust / LEVEL 4
Two correct transfers, one deadlock
EST.45 MIN
01
THEORY / RETRIEVAL
What to restore
- Recognize circular wait caused by request-dependent lock order
- Handle same-resource and invalid-index cases before locking
Validate before taking scarce resources
Self-transfers, invalid indices and invalid amounts should be rejected before acquiring locks. This keeps critical sections small and avoids trying to lock the same non-reentrant mutex twice.
CHECKPOINT
Threads transfer 0→1 and 1→0 concurrently. Which rule directly removes their circular wait?
02 / DEBUGGING
Find and fix the defect
Repair `transfer`: reject invalid operations and acquire two account locks in a stable order while still applying debit and credit to the requested direction.
Initializing editor…
OUTPUT
Runner is waiting for a submission.