[Python-ideas] Tulip / PEP 3156 event loop implementation question: CPU vs. I/O starvation (original) (raw)

Yuval Greenfield ubershmekel at gmail.com
Sat Jan 12 12:03:26 CET 2013

On Sat, Jan 12, 2013 at 1:41 AM, Guido van Rossum <guido at python.org> wrote:

[...]

def hogger():

tulip.geteventloop().callsoon(hogger)

Because callsoon() appends the handler to the ready queue, the while loop will never finish. [...] However this implies that we go back to the I/O polling code more frequently. While the I/O polling code sets the timeout to zero when there's anything in the ready queue, so it won't block, it still isn't free; it's an expensive system call that we'd like to put off until we have nothing better to do. I can imagine various patterns where handlers append other handlers to the ready queue for immediate execution, and I'd make such patterns efficient (i.e. the user shouldn't have to worry about the cost of the I/O poll compared to the amount of work appended to the ready queue). I read your statements as:

Which means you have two options:

IMO core event loops need this configurability but not on a daily basis, e.g. Windows XP's event loop gave priority to the foreground process (i.e. UI events) and Windows Server 2003 gave priority to background processes.

e.g. (warning unoptimized pseudocode follows)

while True: for i in range(io_weight): pop_io() for i in range(event_weight): pop_ready()

note one of the weights can be zero

-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-ideas/attachments/20130112/591141c1/attachment.html>

More information about the Python-ideas mailing list