AtomicLong源码分析

// setup to use Unsafe.compareAndSwapLong for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();

 /**
     * Atomically sets to the given value and returns the old value.
     *
     * @param newValue the new value
     * @return the previous value
     */
    public final long getAndSet(long newValue) {
        while (true) {
            long current = get();
            if (compareAndSet(current, newValue))
                return current;
        }
    }

    public final long getAndIncrement() {
        while (true) {
            long current = get();
            long next = current + 1;
            if (compareAndSet(current, next))
                return current;
        }
    }

public final long getAndAdd(long delta) {
        while (true) {
            long current = get();
            long next = current + delta;
            if (compareAndSet(current, next))
                return current;
        }
    }

    /**
     * Atomically increments by one the current value.
     *
     * @return the updated value
     */
    public final long incrementAndGet() {
        for (;;) {
            long current = get();
            long next = current + 1;
            if (compareAndSet(current, next))
                return next;
        }
    }

/**
     * Atomically sets the value to the given updated value
     * if the current value {@code ==} the expected value.
     *
     * @param expect the expected value
     * @param update the new value
     * @return true if successful. False return indicates that
     * the actual value was not equal to the expected value.
     */
    public final boolean compareAndSet(long expect, long update) {
	return unsafe.compareAndSwapLong(this, valueOffset, expect, update);
    }