At 04:42 PM 7/31/2001 -0700, Paul Prescod wrote:
Dan Sugalski wrote:
...
As for threading, well, that's where things get interesting. Perl's tried it two ways (multiple threads in the same interpreter, and one thread per interpreter, with cloned interpreters) both of which aren't very good. And the global lock thing's not that keen either.
What is the downside of the global lock on the average single processor machine? I tend to think that the "default" threading model should allow simple and easy, everything-shared multi-threading on ordinary machines. Having a multi-processor-friendly advanced mode is a great extension for the wizards.
If you hold the lock during an I/O operation, you'll lose time you could have otherwise used. Getting and releasing a global lock frequently also costs performance you might otherwise have used in other places. Mutex releases require memory coherency, which will force your CPU to flush any pending writes that might be hanging about, which will tend to drop it's efficiency, especially on heavily out-of-order machines like the Alpha. Also, that is a zillion and a half mutex aquisition and releases, most of which you probably have no need of. Even cutting out, say 5-10% of them will be noticeable. (I do work on SMP machines as a rule, so I am a little biased against things that single-thread me when I don't need it--what's the point of 500% idle time?) Dan --------------------------------------"it's like this"------------------- Dan Sugalski even samurai dan@sidhe.org have teddy bears and even teddy bears get drunk