java并发高的情况下用ThreadLocalRandom来生成随机数

protected int next(int bits) {
        long oldseed, nextseed;
        AtomicLong seed = this.seed;
        do {
            oldseed = seed.get();
            nextseed = (oldseed * multiplier + addend) & mask;
        } while (!seed.compareAndSet(oldseed, nextseed));
        return (int)(nextseed >>> (48 - bits));
    }

    @Test
    void test() throws InterruptedException {
        new Thread(()->{
            ThreadLocalRandom random = ThreadLocalRandom.current();
            System.out.println(random.nextInt(100));
        }).start();
        new Thread(()->{
            ThreadLocalRandom random = ThreadLocalRandom.current();
            System.out.println(random.nextInt(100));
        }).start();

        Thread.sleep(100);
    }

    /** Constructor used only for static singleton */
    private ThreadLocalRandom() {
        initialized = true; // false during super() call
    }

    /** The common ThreadLocalRandom */
    static final ThreadLocalRandom instance = new ThreadLocalRandom();

// Unsafe mechanics
private static final sun.misc.Unsafe UNSAFE;
private static final long SEED;
private static final long PROBE;
private static final long SECONDARY;
static {
    try {
        UNSAFE = sun.misc.Unsafe.getUnsafe();
        Class<?> tk = Thread.class;
        SEED = UNSAFE.objectFieldOffset
            (tk.getDeclaredField("threadLocalRandomSeed"));
        PROBE = UNSAFE.objectFieldOffset
            (tk.getDeclaredField("threadLocalRandomProbe"));
        SECONDARY = UNSAFE.objectFieldOffset
            (tk.getDeclaredField("threadLocalRandomSecondarySeed"));
    } catch (Exception e) {
        throw new Error(e);
    }
}

    @sun.misc.Contended("tlr")
    //当前Thread的随机种子 默认值是0
    long threadLocalRandomSeed;

    /** Probe hash value; nonzero if threadLocalRandomSeed initialized */
    @sun.misc.Contended("tlr")
    //用来标志当前Thread的threadLocalRandomSeed是否进行了初始化 0代表没有，非0代表已经初始化 默认值是0
    int threadLocalRandomProbe;

    /** Secondary seed isolated from public ThreadLocalRandom sequence */
    @sun.misc.Contended("tlr")
    //当前Thread的二级随机种子 默认值是0
    int threadLocalRandomSecondarySeed;

public static ThreadLocalRandom current() {
        // 获取当前线程的
        if (UNSAFE.getInt(Thread.currentThread(), PROBE) == 0)
            localInit();
        return instance;
    }

static final void localInit() {
        int p = probeGenerator.addAndGet(PROBE_INCREMENT);
        int probe = (p == 0) ? 1 : p; // skip 0
        long seed = mix64(seeder.getAndAdd(SEEDER_INCREMENT));
        Thread t = Thread.currentThread();
        UNSAFE.putLong(t, SEED, seed);
        UNSAFE.putInt(t, PROBE, probe);
    }

public int nextInt(int bound) {
        if (bound <= 0)
            throw new IllegalArgumentException(BadBound);
        int r = mix32(nextSeed());
        int m = bound - 1;
        if ((bound & m) == 0) // power of two
            r &= m;
        else { // reject over-represented candidates
            for (int u = r >>> 1;
                 u + m - (r = u % bound) < 0;
                 u = mix32(nextSeed()) >>> 1)
                ;
        }
        return r;
    }

final long nextSeed() {
        Thread t; long r; // read and update per-thread seed
        UNSAFE.putLong(t = Thread.currentThread(), SEED,
                       r = UNSAFE.getLong(t, SEED) + GAMMA);
        return r;
    }