In article <mailman.9077.1397051723.18130.python-l...@python.org>, Chris Angelico <ros...@gmail.com> wrote:
> For instance, the above code assumes that print() won't block. You > might think "Duh, how can printing to the screen block?!?", but if > your program's output is being piped into something else, it most > certainly can :) <nostalgia-mode> Heh. One day, a long time ago, I had to investigate why our Vax-11/750 had crashed. I vaguely recollect being called at home on a weekend and having to schlepp into work, but my memory may just be running in auto-story-embelishment mode. Turns out, the machine hadn't really crashed, but it was hung. The console was a LA-120 (http://tinyurl.com/mljyegv), on which was printed various log messages from time to time. It had run out of paper, which was detected by the little out-of-paper microswitch, so it stopped printing. When its input buffer got full, it sent a control-s, which tells the thing on the other end of the serial line to stop sending. Which of course caused the kernel tty driver output buffer to fill, which eventually caused all the print statements by the various system loggers to block, and eventually the whole mess ground to a halt. I put in new paper. The printer proceeded to spit out several hours worth of buffered log messages and the system picked up where it left off. </nostalgia-mode> At Songza, we've been using gevent to do asynchronous I/O. It's an interesting concept. Basically, you write your application code as you normally would, using blocking I/O calls. Gevent then monkey-patches the heck out of the Python library to intercept every call that could possibly block and splice it into a asynchronous task scheduler framework. The amazing thing is that it works. It let us reduce the number of gunicorn worker processes we use by a factor of 6, and handle the same amount of traffic. Of course, monkey-patching is black magic, and sometimes we get hit by really bizarre and difficult to track down bugs. But, to go back to my "technology evolution" scale, gevent is somewhere between avant-garde and what the kewl kids are using (version 1.0 was released in December), so that shouldn't be too surprising. -- https://mail.python.org/mailman/listinfo/python-list
