On Fri, Jun 25, 2010 at 6:41 AM, Michael Bayer <mike...@zzzcomputing.com> wrote: > That's as deep as my thought goes on this and its all based on hypotheticals > since I've never used twisted or greenlets or anything like that. Sorry if > I'm totally off on how gevent/greenlets work, the linked documents didn't > really make it clear how they work for someone who isn't already familiar.
That's completely fair, the docs leave a lot to be desired. Think of greenlets as an implementation of cooperative threading. In typical threading, threads can first of all run in parallel, and the threading is also preemptive, meaning context switches between threads can happen at any time. With greenlets, "threads" are run in a single real OS thread (no parallelism, only multiplexed concurrency), and context switches between threads happen only voluntarily. Why is this useful? Because then you can write non-blocking code in a blocking style. Non-blocking IO is useful for scalable systems development, but event-driven programming (a la twisted) tends to be more tedious and less natural than programming with blocking IO. Plus, most existing code is written against blocking IO, but event-driven programming makes those difficult to reuse. So to answer your first question of what things would look like in an asynchronous world: with cooperative threads like greenlets, everything would hopefully look identical. Embracing event-driven style would indeed spell out significant changes to both sqlalchemy and user code (and that's also not what I'm personally interested in using). Upon closer inspection, it seems that changes might not even be necessary for sqlalchemy, since one can globally set the asynchronous callback for psycopg to hook directly into gevent. http://bitbucket.org/dvarrazzo/psycogreen/src/tip/gevent/psyco_gevent.py -- Yang Zhang http://yz.mit.edu/ -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
