Friday, April 24, 2009

base version ^ current version and CAS

http://en.wikipedia.org/wiki/Compare-and-swap#Implementation_in_C describes a compare-And-Swap algo -- compare my base version with master's current version and update master only if matched. If unmatched, then my base version is stale => can't safely update.

i think iterator uses similar constructs. When an iterator is created from a "master" collection object, it copies master's current version as its immutable base version. Whenever something changes concurrently in master, current version increments. Next iteration will notice it.... and triggers fail fast??

In other words....I guess a Collection object has an auto-incrementing private counter serving as a version number. Each new iterator gets an immutable snapshot of the version number. At each iteration the iterator checks if the "current version #" has incremented which means a change in the collection??

I guess CVS/SVN use similar constructs?

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