The problem with STM is that it adds significant overheads to modification costs. In a "classic" imperative programming language like Java or C#, stores to variables compile down to simple memory writes- very cheap. An STM memory write, by contrast, is 10x or 100x more expensive (depending upon particulars in how the STM is written). So in functional programming languages, like Haskell and Clojure, writes are rare, so the additional cost is minimal.
For example, consider the case where you're sharing a map of objects across multiple threads. The standard way to do that in Clojure is to drop an immutable map into a reference cell. Updating the map only requires one TM write- to the reference cell (one nice thing about immutable data structures is that you don't have to synchronize on them). A Java implementation would have a mutable map, meaning you'd have O(log N) TM writes. If each write takes a few hundred clock cycles, the difference between one write and several dozen writes becomes important. I wrote about this more fully here: http://enfranchisedmind.com/blog/posts/the-problem-with-stm-your-languages-still-suck/ I'm talking about Haskell, but most of my comments apply to Clojure as well. Brian On Fri, May 14, 2010 at 1:35 PM, Angel Java Lopez <ajlopez2...@gmail.com>wrote: > Hi people! > > A 2008 paper, I just received today via twitter > > *Software transactional memory**: why is it only a research toy?* > > http://portal.acm.org/citation.cfm?id=1400228&coll=ACM&dl=ACM&CFID=90273999&CFTOKEN=67127907&ret=1#Fulltext > > Angel "Java" Lopez > http://www.ajlopez.com > http://twitter.com/ajlopez > > > On Fri, May 14, 2010 at 2:27 PM, Brian <brian.fores...@gmail.com> wrote: > >> >> Not directly related to Clojure but I thought this would be of interest to >> folks: >> http://www.infoq.com/news/2010/05/STM-Dropped >> >> >> http://www.reddit.com/r/programming/comments/c4367/microsofts_experiments_with_software/ >> >> >> -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com<clojure%2bunsubscr...@googlegroups.com> > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
