Problem with compareAndSet in redis

[flopezluis]

Hi,

I think there is an error with the method compareAndSet in redis Data 2.1.0.
As far as I know this method is atomic, so it cannot be set the value more than once but if you execute the code below it does.

	public void testCompareSet() {
		for (int i = 0; i < 500; i++) {
		    Inner r = new Inner();
		    new Thread(r).start();
		}
	}
	 private class Inner implements Runnable {

		@Override
		public void run() {
			RedisAtomicInteger atomicInteger = 
					new RedisAtomicInteger("key", redisConnectionFactory);
			System.out.println(atomicInteger.compareAndSet(0, 1));
		}
	 }

The output of this is:

false
false
false
false
true
false
false
false
false
false
false
false
false
true
false
false
false
false
true
false
false
false
true
false
false
.......

Am I missing anything?

Thanks

[flopezluis]

I'm looking into the code:

	public boolean compareAndSet(final int expect, final int update) {
		return generalOps.execute(new SessionCallback<Boolean>() {

			@SuppressWarnings("unchecked")
			
			public Boolean execute(RedisOperations operations) {
				for (;;) {
					operations.watch(Collections.singleton(key));
					if (expect == get()) {
						generalOps.multi();
						set(update);
						if (operations.exec() != null) {
							return true;
						}
					}
					{
						return false;
					}
				}
			}
		});
	}

And I'm wondering if the call to MULTI shouldn't be done before the get, so it makes sure that only one reads the old value.