What is the synchronization cost of calling a synchronized method from a synchronized method?

Question

Is there any difference in performance between this

synchronized void x() {
    y();
}

synchronized void y() {
}

and this

Answer 1

Why not test it!? I ran a quick benchmark. The benchmark() method is called in a loop for warm-up. This may not be super accurate but it does show some consistent interesting pattern.

public class Test {
    public static void main(String[] args) {

        for (int i = 0; i < 100; i++) {
            System.out.println("+++++++++");
            benchMark();
        }
    }

    static void benchMark() {
        Test t = new Test();
        long start = System.nanoTime();
        for (int i = 0; i < 100; i++) {
            t.x();
        }
        System.out.println("Double sync:" + (System.nanoTime() - start) / 1e6);

        start = System.nanoTime();
        for (int i = 0; i < 100; i++) {
            t.x1();
        }
        System.out.println("Single sync:" + (System.nanoTime() - start) / 1e6);
    }
    synchronized void x() {
        y();
    }
    synchronized void y() {
    }
    synchronized void x1() {
        y1();
    }
    void y1() {
    }
}

Results (last 10)

+++++++++
Double sync:0.021686
Single sync:0.017861
+++++++++
Double sync:0.021447
Single sync:0.017929
+++++++++
Double sync:0.021608
Single sync:0.016563
+++++++++
Double sync:0.022007
Single sync:0.017681
+++++++++
Double sync:0.021454
Single sync:0.017684
+++++++++
Double sync:0.020821
Single sync:0.017776
+++++++++
Double sync:0.021107
Single sync:0.017662
+++++++++
Double sync:0.020832
Single sync:0.017982
+++++++++
Double sync:0.021001
Single sync:0.017615
+++++++++
Double sync:0.042347
Single sync:0.023859

Looks like the second variation is indeed slightly faster.