https://github.com/juju/juju/wiki/Guidelines-for-writing-workers
On Mon, Jun 1, 2015 at 3:32 PM, Nate Finch <[email protected]> wrote: > Totally belongs on the wiki. > > On Mon, Jun 1, 2015 at 8:45 AM, John Meinel <[email protected]> > wrote: > >> This is one of those things that should probably end up on the Wiki. >> Thanks for writing it up. >> >> John >> =:-> >> >> >> On Thu, May 28, 2015 at 5:34 PM, William Reade < >> [email protected]> wrote: >> >>> Hi all >>> >>> I've noticed that there's a lot of confusion over how to write a useful >>> worker. Here follow some guidelines that you should be *very* certain of >>> yourself before breaking (and probably talk to me about anyway). If there's >>> any uncertainty about these, I'm more than happy to expand. >>> >>> * If you really just want to run a dumb function on its own goroutine, >>> use worker.NewSimpleWorker. >>> >>> * If you just want to do something every <period>, use >>> worker.NewPeriodicWorker. >>> >>> * If you want to react to watcher events, you should probably use >>> worker.NewNotifyWorker or worker.NewStringsWorker. >>> >>> * If your worker has any methods outside the Worker interface, DO NOT >>> use any of the above callback-style workers. Those methods, that need to >>> communicate with the main goroutine, *need* to know that goroutine's state, >>> so that they don't just hang forever. >>> >>> * To restate the previous point: basically *never* do a naked channel >>> send/receive. If you're building a structure that makes you think you need >>> them, you're most likely building the wrong structure. >>> >>> * If you're writing a custom worker, and not using a tomb.Tomb, you >>> are almost certainly doing it wrong. Read the blog post [0] or, hell, just >>> read the code [1] -- it's less than 200 lines and it's about 50% comments. >>> >>> * If you're letting tomb.ErrDying leak out of your workers to any >>> clients, you are definitely doing it wrong -- you risk stopping another >>> worker with that same error, which will quite rightly panic (because that >>> tomb is *not* yet dying). >>> >>> * If it's possible for your worker to call .tomb.Done() more than >>> once, or less than once, you are *definitely* doing it very very wrong >>> indeed. >>> >>> * If you're using .tomb.Dead(), you are very probably doing it wrong >>> -- the only reason (that I'm aware of) to select on that .Dead() rather >>> than on .Dying() is to leak inappropriate information to your clients. They >>> don't care if you're dying or dead; they care only that the component is no >>> longer functioning reliably and cannot fulfil their requests. Full stop. >>> Whatever started the component needs to know why it failed, but that parent >>> is usually not the same entity as the client that's calling methods. >>> >>> * If you're using worker/singular, you are quite likely to be doing it >>> wrong, because you've written a worker that breaks when distributed. Things >>> like provisioner and firewaller only work that way because we weren't smart >>> enough to write them better; but you should generally be writing workers >>> that collaborate correctly with themselves, and eschewing the temptation to >>> depend on the funky layer-breaking of singular. >>> >>> * If you're passing a *state.State into your worker, you are almost >>> certainly doing it wrong. The layers go worker->apiserver->state, and any >>> attempt to skip past the apiserver layer should be viewed with *extreme* >>> suspicion. >>> >>> * Don't try to make a worker into a singleton (this isn't particularly >>> related to workers, really, singleton is enough of an antipattern on its >>> own [2] [3] [4]). Singletons are basically the same as global variables, >>> except even worse, and if you try to make them responsible for goroutines >>> they become more horrible still. >>> >>> Did I miss anything major? Probably. If so, please remind me. >>> >>> Cheers >>> William >>> >>> >>> [0] http://blog.labix.org/2011/10/09/death-of-goroutines-under-control >>> [1] launchpad.net/tomb (apparently... we really ought to be using v2, >>> though) >>> [2] >>> https://sites.google.com/site/steveyegge2/singleton-considered-stupid >>> [3] >>> http://jalf.dk/blog/2010/03/singletons-solving-problems-you-didnt-know-you-never-had-since-1995/ >>> [4] >>> http://programmers.stackexchange.com/questions/40373/so-singletons-are-bad-then-what/ >>> >>> -- >>> Juju-dev mailing list >>> [email protected] >>> Modify settings or unsubscribe at: >>> https://lists.ubuntu.com/mailman/listinfo/juju-dev >>> >>> >> >> -- >> Juju-dev mailing list >> [email protected] >> Modify settings or unsubscribe at: >> https://lists.ubuntu.com/mailman/listinfo/juju-dev >> >> >
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