Question

I was trying some benchmark over these two ( Software transactional memory & Atomic Operation , i guess both are not same ), though i have not done much using STM ( it seems hard to use ) ,but i successfully tried counting benchmark i.e. all the threads are incrementing a shared counter 50mn times, and noticed that atomic operation works better than STM.

So i want to know since STM are not fully developed , do they perform well in realistic situation than Atomic operation?
Has some one switched to other because of performance ? please share the information..

related journal i found on the web is Concurrent programming without locks

P.S. I am using JAVA as programming language. STM :- multi-verse. AtomicOperatinn: AtomicInteger.

Answer 1

Atomic operations and STMs are very different beasts. In particular, atomic operations are much “lower level” constructs – in fact, atomic operations of various kinds are generally used to implement STM. Basically:

• An atomic operation allows you to do a concurrency-safe update of a single object. This is easy and fast, typically just a single instruction on modern hardware.
• STM allows you do to a concurrency-safe update of multiple objects. This is complex.

STM systems therefore need to add additional book-keeping overhead to manage the complexity of a transactional update – so if you only need to update a single object an atomic operation will nearly always be faster.

Also, you should be aware that there is no consensus on the best way to design STM systems – it’s an active research topic and there are many tradeoffs involved. So what performs well on one STM system might not perform well on another STM system etc.

For example: my favourite STM system at the moment is Clojure’s – it’s particularly appealing because it supports multi-version concurrency control and never impedes readers – which gives a significant performance advantage in many common scenarios.