How does ReentrantLock synchronize?

Question

I have looked at the Java API for ReentrantLock and what I can see is that no synchronization is used with the synchronized keyword. Is it in the below method in AbstractQueuedSynchronizer (that ReentrantLock is refering to when trying to aquire a lock) that synchronizes the object? Since the compareAndSwapInt is a native method, is the synchronization made at the native level/code?

protected final boolean compareAndSetState(int expect, int update) {
    // See below for intrinsics setup to support this
    return unsafe.compareAndSwapInt(this, stateOffset, expect, update);
}

score 3 · Accepted Answer · answered Apr 27 '12 at 13:57

3

The implementation will likely be different per JDK. Sun (now Oracle) implementation, for example, does it via sun.misc.Unsafe ( http://www.docjar.com/docs/api/sun/misc/Unsafe.html )

I once blogged about how Java concurrency in unsafe :)

answered Apr 27 '12 at 13:57

Pavel Veller

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score 1 · Answer 2 · answered Apr 27 '12 at 13:56

1

You're correct: in Oracle's JDK, ReentrantLock is implemented in terms of the native compare-and-swap primitive (plus a fair amount of Java code on top of it), and not in terms of the synchronized keyword.

answered Apr 27 '12 at 13:56

NPE

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How does ReentrantLock synchronize?

2 Answers2