The procedure is:

1. UAVBuffer.IncrementCounter() in first dispatch.
2. UAV barrier waits for the previous op is done.
3. Read the counter value by UAVBuffer.Load(0)

I always got the value "0".

I used PIX to check what's going on:

It shows that the reading op should be fine. 

And below is what a counter buffer view in PIX(in the first dispatch):

what the counter buffer view show in counter reading dispatch:

I init counter as a 32-bit(4 bytes) buffer, I don't understand why PIX showed the buffer count is 27,550. Does this make my counter reading got the wrong value?