Hi Aroman, Your approach using the WaitGroup is definitely better in this toy example. The reason I didn't use the WaitGroup is because the non-toy example is wrapping the HTTP Server handler. I have no way to inject an "add" before the goroutine is created since that's handled by Go's HTTP Server without re-implementing the accept->handle loop using the listener.
Apologies for not giving the full context in the example. I'm not sure how it could block an outstanding task since the closed channel is called before the Lock(), so no additional calls to RLock will be made at that point, and the Lock will just wait until all of the RLocks are complete. Regarding your testing strategy, I do like it better than any of my current strategy; however, There still is a chance that a task could complete between lines 90 and 91: h.Close() events <- ALL_TASKS_FINISHED So this doesn't solve the racy-ness I'm concerned about unless you put an arbitrary sleep in the handlers, which I'm trying to avoid. On Tuesday, 13 September 2016 12:34:17 UTC-7, aro...@gmail.com wrote: > > The WaitGroup is better than the lock approach, since the lock approach > could block an outstanding task. The key to using waitgroups is to call > Add() outside of goroutines that might call done: > > https://play.golang.org/p/QVWoy8fCmI > > On Tuesday, September 13, 2016 at 12:19:16 PM UTC-7, Evan Digby wrote: >> >> Hi John, >> >> Thanks for the reply. I've tried many incarnations that include >> WaitGroups; however, none seem to achieve the desired result. >> >> If I add a WaitGroup with a defer done in the handler, and then wait >> after the Close() then the test itself implements the requirement and won't >> protect from future refactors. There's no way to test that a WaitGroup is >> done without waiting for it, and even if there was it would be racy because >> between the Close() and WaitGroup wait call tasks could complete. If I >> wrapped the wait and the done in goroutines to see which one happened >> first, also racy. >> >> If you have something else in mind can you elaborate on how it would help >> in this case? >> >> Thanks again! >> >> Evan >> >> On Tuesday, 13 September 2016 12:01:29 UTC-7, John Souvestre wrote: >>> >>> Have you considered using a sync.WaitGroup? >>> >>> >>> >>> John >>> >>> John Souvestre - New Orleans LA >>> >>> >>> >>> *From:* golan...@googlegroups.com [mailto:golan...@googlegroups.com] *On >>> Behalf Of *Evan Digby >>> *Sent:* 2016 September 13, Tue 13:56 >>> *To:* golang-nuts >>> *Subject:* [go-nuts] Having difficulty testing this "cleanly" >>> >>> >>> >>> Has anyone come across a good way, non-racy way to ensure that N tasks >>> are guaranteed to be completed after a function is called? Essentially I >>> have a “Close” function that must be guaranteed to block until all tasks >>> are finished. Achieving this was pretty simple: wrap each task in an RLock, >>> and then a Lock on close. >>> >>> >>> >>> Example: https://play.golang.org/p/7lhBPUhkUE >>> >>> >>> >>> Now I want to write a solid test to guarantee Close will meet that >>> requirement of all tasks must finish first for posterity. In that example, >>> try commenting out the RLock/RUnlock on lines 25/26. You'll see that it no >>> longer outputs many, if any, lines. I'm trying to prevent that from >>> happening in the future by some cowboy refactor! >>> >>> >>> >>> All of the ways I can come up with involve Sleeping or launching more >>> tasks than I _think_ can be finished in time--obviously not good! >>> >>> >>> >>> I feel like I must be missing some obvious way to test this and I'll end >>> up feeling silly once someone replies with the solution. I'm okay with that! >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to golang-nuts...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
