A holds lock 4 and waits for lock 7. B holds lock 7 and waits for lock 4. The locks block without timeout, and neither thread releases its lock first. What has happened?

• Both threads can acquire the other lock without waiting.
• Both threads are deadlocked in a cycle of waiting.
• Only A is waiting; B can finish without acquiring lock 4.

Which set names the four necessary conditions for resource deadlock?

• Mutual exclusion, hold and wait, no preemption, circular wait
• Mutual exclusion, repeated retries, automatic rollback, circular wait
• Shared access, hold and wait, automatic preemption, delayed responses

A thread waiting for a lock while holding no resource meets the hold-and-wait condition.

Every thread acquires lock 2 before lock 5 when it needs both. What does this rule prevent?

• Circular wait involving only these two locks
• Every delay caused by either of these two locks
• Every deadlock caused by any resource in the program

Thread P waits for a lock held by thread Q. What edge belongs in a thread-only wait-for graph?

• Q to P, pointing from the holder to the waiting thread
• P to Q, but only after P releases any locks it holds
• P to Q, pointing from the waiting thread to the holder

A resource system can safely abort a holder, undo its partial work, and forcibly reclaim its resources. Which deadlock condition does this remove?

• Mutual exclusion: a resource permits only one holder at a time
• No preemption: held resources cannot be forcibly reclaimed
• Circular wait: each thread waits for the next thread in a cycle

A complete directed wait-for graph has edges U to V, V to W and W to U. Sam reverses every arrow and says the cycle disappears. Which check corrects his claim?

• Reversing the arrows removes the cycle because each edge now points toward a previous holder.
• Reversing the arrows removes the cycle because a cycle requires its original starting thread.
• The reversed edges still form the cycle U to W to V to U.

R and S are already deadlocked on locks 8 and 9. A patch gives future executions one acquisition order. What should the team conclude about the stuck run?

• The patch makes the held locks available automatically, so the stuck run needs no recovery.
• The rule prevents future cycles; the stuck run still needs safe recovery.
• The patch proves the stuck run was waiting for input, so its held locks need no attention.