Four Conditions, and the One Worth Removing

Five things this topic established, and where each one was.

What the topic established, and which card it was on
The thing	Where
A deadlock is a cycle of threads each holding what another wants	Two Threads, Two Locks
Two correct methods taking the same locks in opposite orders is enough	A Transfer Between Two Accounts
Four conditions must hold at once; removing any one prevents it	The Four Conditions a Deadlock Needs
A global lock ordering is the condition you can remove for free	Fixing the Transfer by Giving the Two Locks an Order
Idle threads stuck is deadlock; busy threads stuck is livelock	Deadlock, Livelock and Starvation

No single method can deadlock on its own, so no amount of reading one method will find it. What causes a deadlock is two pieces of code disagreeing about an order, and the fix is a decision the whole program keeps.

Java
Concurrency