On 03/03/2010 01:43 AM, Henry Robinson wrote:
Just to illustrate one of the primitives you're looking for: an
AtomicInteger equivalent would be fairly easy to construct, with nearly
identical semantics to the Java version.

Let's say a given znode has four bytes of data that represent an integer
value. Get operations or set operations are easy, as ZK will make sure that
all operations are atomic, so they happen in a linearizable order. A
get-and-set operation can be performed by reading the znode via getData, and
performing a conditional update using the version number of the znode that
was returned as part of the getData operation. ZooKeeper's setData operation
takes an optional version number (set it to -1 to ignore it) which tells the
operation to succeed only if the znode's version hasn't changed since. Other
operations can use this procedure as a base.

This is exactly how Java's getAndSet is implemented - neither implementation
is wait-free, but they are still lock-free: some process will always make

Hope this helps - let me know if you'd like more detail on exactly how to
build this.


Ah! Didn't see that "version" parm on the setData call. Yes, that makes atomic operations incredibly easy!

Thanks much for the explanation, Henry!


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