On Tue, Jan 3, 2012 at 7:40 PM, Mike Meyer <m...@mired.org> wrote: > STM is a relatively new technology being experimented with in newer > languages, and in a number of 3rd party libraries (both Peak [#Peak]_ > and Kamaelia [#Kamaelia]_ provide STM facilities).
I don't know about Kamaelia, but PEAK's STM (part of the Trellis event-driven library) is *not* an inter-thread concurrency solution: it's actually used to sort out the order of events in a co-operative multitasking scenario. So, it should not be considered evidence for the practicality of doing inter-thread co-ordination that way in pure Python. A suite is marked > as a `transaction`, and then when an unlocked object is modified, > instead of indicating an error, a locked copy of it is created to be > used through the rest of the transaction. If any of the originals are > modified during the execution of the suite, the suite is rerun from > the beginning. If it completes, the locked copies are copied back to > the originals in an atomic manner. > I'm not sure if "locked" is really the right word here. A private copy isn't "locked" because it's not shared. The disadvantage is that any code in a transaction must be safe to run > multiple times. This forbids any kind of I/O. > More precisely, code in a transaction must be *reversible*, so it doesn't forbid any I/O that can be undone. If you can seek backward in an input file, for example, or delete queued output data, then it can still be done. Even I/O like re-drawing a screen can be made STM safe by making the redraw occur after a transaction that reads and empties a buffer written by other transactions. For > instance, combining STM with explicit locking would allow explicit > locking when IO was required, I don't think this idea makes any sense, since STM's don't really "lock", and to control I/O in an STM system you just STM-ize the queues. (Generally speaking.)
_______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
