AtomicLong AtomicDouble AtomicInteger

Atomic+数字类型 大多都持有一个静态的Unsafe对象,通过unsafe 对属性在类对象的offset cas直接操作物理内存实现对数据的修改

public class AtomicLong extends Number implements java.io.Serializable {
    private static final long serialVersionUID = 1927816293512124184L;

    // setup to use Unsafe.compareAndSwapLong for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe(); //Unsafe是单例的
    private static final long valueOffset;

    /**
     * Records whether the underlying JVM supports lockless
     * compareAndSwap for longs. While the Unsafe.compareAndSwapLong
     * method works in either case, some constructions should be
     * handled at Java level to avoid locking user-visible locks.
     */
    static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();

public final boolean compareAndSet(long expect, long update) {
    return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
}

public final boolean weakCompareAndSet(long expect, long update) {
    return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
}

public final long getAndIncrement() {
    return unsafe.getAndAddLong(this, valueOffset, 1L);
}

/**
 * Atomically decrements by one the current value.
 *
 * @return the previous value
 */
public final long getAndDecrement() {
    return unsafe.getAndAddLong(this, valueOffset, -1L);
}

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}