Thanks for another clear answer! I'll simply ignore zc.twist (for now
at least) and set up a classic thread pool.
I'll still probably use zc.twist's source as an example of how to
write transaction retrial on ConflicErrors and ClientDisconnecteds as
I haven't found anything similar elsewhere.
Erik
2011/7/29 Gary Poster gary.pos...@gmail.com:
On Jul 28, 2011, at 6:38 PM, Erik Allik wrote:
Gary, since you're the author of zc.twist (as I understand), I take
this as an exhaustive answer, and thank you :)
However, I'm still curious to know zc.twist would provide any benefit
when used together with a thread pool.
The thread examples in its README (which I find hard to understand)
indicate that there must be some meaning to using zc.twist with
threads.
The threads in the README are there to let me explore a running reactor
within the doctest. They are not anything to emulate.
The README overstates zc.twist's usefulness. As you point out, it blocks.
If you assume that the ZODB is functioning normally, it won't block much
but with standard definitions of blocking, it fails. For zc.async, that's
fine--but a while True loop and a time.sleep() to give some breathing room
probably would have been fine, with hindsight, and much simpler. The use of
Twisted is a very questionable convenience, and the way zc.async uses Twisted
is not to be copied 99% or more of the time.
Gary
Thanks again and best regards,
Erik
2011/7/29 Gary Poster gary.pos...@gmail.com:
Hello Erik. As the author, I'll suggest that you move on to a ZODB
connection pool used by the usual Twisted-provided thread pool. zc.twist
is maybe interesting and maybe clever, but of very limited usefulness. I
suspect it is only used in zc.async, and that's probably as it should be.
It's a case of premature generalization.
If you are going to use Twisted in anything like a normal way, and the ZODB
in anything like a normal way, use a connection pool and threads.
Best,
Gary
On Jul 28, 2011, at 4:12 PM, Erik Allik wrote:
Hello everyone,
I hope this is the right mailing list to post this question to.
I'm trying to build an Twisted application that uses ZODB and I've
also found zc.twist.
I've read its README as well as the source code to try to understand
how exactly and why I should use zc.twist, and also asked the same
questions on irc.freenode.net #zope but without a conclusive answer.
What I'm not able to understand is whether using zc.twist will allow
me to do all ZODB access in the main Twisted thread, or if still need
to set up a thread pool and deferToThread any code that accesses the
DB.
The README of zc.twist has:
Everything can be done within the main thread, so it can be full-bore
Twisted usage, without threads.
However, looking at the source code of zc.twist, I cannot find any
reference to async communication (callbacks/polling) with ZODB, so
it's difficult to conclude that all DB access is non-blocking and can
be done in a single thread. Also, there are some examples with threads
in the README.
I would highly appreciate if somebody with a clearer understanding of
this could explain to me whether I in fact need to set up a thread
pool, and in any case, what exactly is zc.twist for regardless of
whether it needs to be used with a threadpool or not.
Thanks in advance!
Regards,
Erik Allik
P.S. I'd be very thankful for any references to open source
projects/code using ZODB with Twisted, or even zc.twist (besides
zc.async).
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