On Sun, Jun 25, 2017 at 4:54 PM Chris Jerdonek <chris.jerdo...@gmail.com> wrote:
> The read-write operations I'm protecting will have coroutines inside > that need to be awaited on, so I don't think I'll be able to take > advantage to that extreme. > > But I think I might be able to use your point to simplify the logic a > little. (To rephrase, you're reminding me that context switches can't > happen at arbitrary lines of code. I only need to be prepared for the > cases where there's an await / yield from.) The "secret" Guido refers to we should pull out front and center, explicitly at all times - asynchronous programming is nothing more than cooperative multitasking. Patterns suited for preemptive multi-tasking (executive-based, interrupt based, etc.) are suspect, potentially misplaced when they show up in a cooperative multitasking context. To be a well-behaved (capable of effective cooperation) task in such a system, you should guard against getting embroiled in potentially blocking I/O tasks whose latency you are not able to control (within facilities available in a cooperative multitasking context). The raises a couple of questions: to be well-behaved, simple control flow is desireable (i.e. not nested layers of yields, except perhaps for a pipeline case); and "read/write" control from memory space w/in the process (since external I/O is generally not for async) begs the question: what for? Eliminate globals, encapsulate and limit access as needed theough usual programming methods. I'm sure someone will find an edgecase to challenge my above rule-of-thumb, but as you're new to this, I think this is a pretty good place to start. Ask yourself if what your trying to do w/ async is suited for async. Cheers, Yarko > > > --Chris > > > On Sun, Jun 25, 2017 at 2:30 PM, Guido van Rossum <gvanros...@gmail.com> > wrote: > > The secret is that as long as you don't yield no other task will run so > you > > don't need locks at all. > > > > On Jun 25, 2017 2:24 PM, "Chris Jerdonek" <chris.jerdo...@gmail.com> > wrote: > >> > >> Thank you. I had seen that, but it seems heavier weight than needed. > >> And it also requires locking on reading. > >> > >> --Chris > >> > >> On Sun, Jun 25, 2017 at 2:16 PM, Andrew Svetlov > >> <andrew.svet...@gmail.com> wrote: > >> > There is https://github.com/aio-libs/aiorwlock > >> > > >> > On Mon, Jun 26, 2017 at 12:13 AM Chris Jerdonek > >> > <chris.jerdo...@gmail.com> > >> > wrote: > >> >> > >> >> I'm relatively new to async programming in Python and am thinking > >> >> through possibilities for doing "read-write" synchronization. > >> >> > >> >> I'm using asyncio, and the synchronization primitives that asyncio > >> >> exposes are relatively simple [1]. Have options for async read-write > >> >> synchronization already been discussed in any detail? > >> >> > >> >> I'm interested in designs where "readers" don't need to acquire a > lock > >> >> -- only writers. It seems like one way to deal with the main race > >> >> condition I see that comes up would be to use loop.time(). Does that > >> >> ring a bell, or might there be a much simpler way? > >> >> > >> >> Thanks, > >> >> --Chris > >> >> > >> >> > >> >> [1] https://docs.python.org/3/library/asyncio-sync.html > >> >> _______________________________________________ > >> >> Async-sig mailing list > >> >> Async-sig@python.org > >> >> https://mail.python.org/mailman/listinfo/async-sig > >> >> Code of Conduct: https://www.python.org/psf/codeofconduct/ > >> > > >> > -- > >> > Thanks, > >> > Andrew Svetlov > >> _______________________________________________ > >> Async-sig mailing list > >> Async-sig@python.org > >> https://mail.python.org/mailman/listinfo/async-sig > >> Code of Conduct: https://www.python.org/psf/codeofconduct/ > _______________________________________________ > Async-sig mailing list > Async-sig@python.org > https://mail.python.org/mailman/listinfo/async-sig > Code of Conduct: https://www.python.org/psf/codeofconduct/ >
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