RecapDifficulty: Advanced1 min

Recap: Locks

Which object is locked, what a lock publishes, reentrancy, ReentrantLock, and sequences of calls.

Locks come down to the five ideas below, each listed with the card that covers it.

What the topic established, and which card it was on
The idea	Where
A `synchronized` instance method locks `this`; the static form locks the class	static synchronized Locks the Class, Not the Instance
Releasing a lock publishes everything written inside it, to anyone taking the same lock	Lock Visibility: Releasing a Lock Publishes Every Write
Locks are reentrant: held by the thread, not the block	Reentrant Locks: Taking a Lock the Thread Already Holds
`ReentrantLock` adds timeouts and interruptible waiting, and needs a `finally`	synchronized vs ReentrantLock
Every method being atomic says nothing about a sequence of two calls	Synchronised Methods Do Not Make a Sequence of Calls Atomic

A lock protects a region, and the region has to be as large as the operation. Deciding where the operation really starts and ends is the real work, and the keyword does none of it for you.

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