A more complex form of deadlock can emerge in a scenario which involves nested locking: two or more competing threads and two or more locks. Here, let's take the simplest case: a scenario with two threads (A and B) working with two locks (L1 and L2).
Let's say that this is what unfolds over the vertical timeline, as the following table reveals:
| Time | Thread A | Thread B |
| t1 | Attempt to take lock L1 | Attempt to take lock L2 |
| t2 | Gets lock L1 | Gets lock L2 |
| t3 | <--- In critical section of L1 ---> | <--- In critical section of L2 ---> |
| t4 | Attempt to take lock L2 | Attempt to take lock L1 |
| t5 | Block on L2 being unlocked | Block on L1 being unlocked |
| <waits forever: deadlock> | <waits forever: deadlock> |
It's quite clear that each thread waits for the other to unlock the lock it wants; thus, each thread waits forever, guaranteeing a deadlock. This kind of deadlock is often called the deadly embrace or the ABBA deadlock.