On Mon, Nov 23, 2020 at 6:05 AM 叶志辉 <yezhihui19830...@gmail.com> wrote: > > A little confused by the test case of `singleflight` of > `internal/singleflight`. > > Which is the codes singleflight. > > 1. wg1 > > Purpose for wg1 is as commented as: > > // At least one goroutine is in fn now and all of them have at > // least reached the line before the Do. > > Confused about `At least one goroutine is in fn `，what test situation for > this? > I mean, for example, if 'no one goroutine is in fn', would be any problem?
The point of the test is to make sure that the singleflight code only makes a single concurrent call to the function. Writing to c will cause fn to return. There should only be one goroutine in fn at a time. Waiting until at least one goroutine is in fn before writing to c maximizes the possibility of detecting a bug that causes fn to be called more than once simultaneously. > 2. the channel `c` > > Each `fn` just read from `c`, and write value back, as codes: > > v := <-c > c <- v // pump; make available for any future calls > > Don't really get the purpose. We are testing that fn is only called once concurrently. There can be multiple calls to fn. Writing a value to the channel after reading one is an easy way to make sure that the next call to fn will succeed. > 3. got value > The expect value of got is: 0<got<N. > > Why not 0<got<=N, I mean there is case got==N? got == n means that every all to g.Do called fn. While that is technically possible, it is quite unlikely, because the use of wg1 means that all n goroutines will be at least very close to calling g.Do before fn ever returns. So got == n suggests that fn was called concurrently by multiple goroutines, which would be a bug. Ian -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcV8Ly2iU0PfU4J_9QPxGWer%2BxSq5x%2B%3DXhDGFD5Xv9X9ZQ%40mail.gmail.com.
