AtomicInteger 源码分析

private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long valueOffset;

static {
    try {
        valueOffset = unsafe.objectFieldOffset
            (AtomicInteger.class.getDeclaredField("value"));
    } catch (Exception ex) { throw new Error(ex); }
}

private volatile int value;

// 获取 & 自增
public final int getAndIncrement() {
    return unsafe.getAndAddInt(this, valueOffset, 1);
}
// 自增 & 获取
public final int incrementAndGet() {
    return unsafe.getAndAddInt(this, valueOffset, 1) + 1;
}
// 获取 & 自减
public final int getAndDecrement() {
    return unsafe.getAndAddInt(this, valueOffset, -1);
}
// 自减 & 获取
public final int decrementAndGet() {
    return unsafe.getAndAddInt(this, valueOffset, -1) - 1;
}

public final int getAndAddInt(Object var1, long var2, int var4) {
    int var5;
    do {
        var5 = this.getIntVolatile(var1, var2);
    } while(!this.compareAndSwapInt(var1, var2, var5, var5 + var4));

    return var5;
}