14 AtomicInteger

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public class AtomicIntegerTest {

    @Test
    void test() {
        AtomicInteger atomicInteger = new AtomicInteger();
        assertThat(atomicInteger.get()).isEqualTo(0);
        assertThat(atomicInteger.incrementAndGet()).isEqualTo(1);
    }
}

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// value 字段是 volatile 的，可以保证可见性。
public final int incrementAndGet() {
    // U 是 Unsafe 类型,  getAndAddInt 实际是 CAS 操作
    return U.getAndAddInt(this, VALUE, 1) + 1;
}

@IntrinsicCandidate
public final int getAndAddInt(Object o, long offset, int delta) {
    int v;
    do {
        v = getIntVolatile(o, offset);
    } while (!weakCompareAndSetInt(o, offset, v, v + delta));
    return v;
}

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public final boolean compareAndSet(int expectedValue, int newValue) {
    return U.compareAndSetInt(this, VALUE, expectedValue, newValue);
}