"I have a mind like a steel... uh... thingy." Patrick Logan's weblog.

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Thursday, August 16, 2007


Brit Butler left a good comment in a recent post...

I've watched this video and also read the slides from Sweeney's POPL presentation. Sweeney basically comes out on the side of Transaction Memory without saying much about the message passing model (though he later goes in to detail on LtU). I think TM is ugly, regardless of what Simon Peyton-Jones or Sweeney says. They're smart people but it seems like an ugly hack of a system. It is the maintenance of a style that is begging for deprecation. I'd kind of hate to see us save it. All the same, their intelligence makes me wonder if message-passing really can't scale to Sweeney's needs. What are your thoughts on where some shared state is necessary? Is that handled well in Erlang? Do Sweeney and Peyton-Jones arguments really hold weight? Is it just a "right tool for the job" kind of thing?
The best anyone can say about STM is the jury is still out. All I can say for sure is it is not my cup of tea for the systems I've been involved with over the last 25+ years, which are actually fairly wide ranging.

SPJ, et al. are *extremely* smart and capable people, far more than I am, so I have to give them some leaway, and perhaps I will be swayed toward STM for some reason currently beyond my line of sight. I admire nearly everything else about Haskell and GHC other than STM.

An irony for me, as for the "right tool for the job" argument is this:

I can see someone making the argument in some domain I don't usually work in that shared memory threads are better than shared nothing message passing for performance reasons. Some hard-real time scenario (I think I was real tired when I wrote that. Must have been thinking back to the days when I'd get into "Is automatic garbage collection practical?" debates. Nobody has those anymore, do they? Because I've got some real good arguments for GC.), some huge number crunching scenario, etc. where every byte and every cycle has to count in the extreme. But the irony then is that STM seems far more suited to a language like Haskell, which is also unlikely to be suited for these performance scenarios.

My only fear is that for the masses including myself, we need *simple* mechanisms, and the fewer of those, the better. Shared nothing messages seem to scale up, out, and down. STM seems more complicated, and an incomplete solution, and only a solution for shared memory. No thanks, at least until bigger brains than my own can show me why I should change my mind. They seem sidetracked on this one.

1 comment:

Anonymous said...

Smart people like complex solutions because they can handle them:


Best Explanation I've seen (for STM, C++ and a whole lot else). I've seen it elsewhere before too, but I am not sure where.


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Portland, Oregon, United States
I'm usually writing from my favorite location on the planet, the pacific northwest of the u.s. I write for myself only and unless otherwise specified my posts here should not be taken as representing an official position of my employer. Contact me at my gee mail account, username patrickdlogan.