Yes but only for a single reader - any concurrent reader is going to park/deschedule.
There’s a reason RW locks exist - and I think it is pretty common - but agree to disagree :) > On Jan 30, 2023, at 6:23 PM, Ian Lance Taylor <i...@golang.org> wrote: > > On Mon, Jan 30, 2023 at 1:00 PM Robert Engels <reng...@ix.netcom.com> wrote: >> >> Pure readers do not need any mutex on the fast path. It is an atomic CAS - >> which is faster than a mutex as it allows concurrent readers. On the slow >> path - fairness with a waiting or active writer - it degenerates in >> performance to a simple mutex. >> >> The issue with a mutex is that you need to acquire it whether reading or >> writing - this is slow…. (at least compared to an atomic cas) > > The fast path of a mutex is also an atomic CAS. > > Ian > >>>> On Jan 30, 2023, at 2:24 PM, Ian Lance Taylor <i...@golang.org> wrote: >>> >>> On Mon, Jan 30, 2023 at 11:26 AM Robert Engels <reng...@ix.netcom.com> >>> wrote: >>>> >>>> I don’t think that is true. A RW lock is always better when the reader >>>> activity is far greater than the writer - simply because in a good >>>> implementation the read lock can be acquired without blocking/scheduling >>>> activity. >>> >>> The best read lock implementation is not going to be better than the >>> best plain mutex implementation. And with current technology any >>> implementation is going to require atomic memory operations which >>> require coordinating cache lines between CPUs. If your reader >>> activity is so large that you get significant contention on a plain >>> mutex (recalling that we are assuming the case where the operations >>> under the read lock are quick) then you are also going to get >>> significant contention on a read lock. The effect is that the read >>> lock isn't going to be faster anyhow in practice, and your program >>> should probably be using a different approach. >>> >>> Ian >>> >>>>>> On Jan 30, 2023, at 12:49 PM, Ian Lance Taylor <i...@golang.org> wrote: >>>>> >>>>> On Sun, Jan 29, 2023 at 6:34 PM Diego Augusto Molina >>>>> <diegoaugustomol...@gmail.com> wrote: >>>>>> >>>>>> From times to times I write a scraper or some other tool that would >>>>>> authenticate to a service and then use the auth result to do stuff >>>>>> concurrently. But when auth expires, I need to synchronize all my >>>>>> goroutines and have a single one do the re-auth process, check the >>>>>> status, etc. and then arrange for all goroutines to go back to work >>>>>> using the new auth result. >>>>>> >>>>>> To generalize the problem: multiple goroutines read a cached value that >>>>>> expires at some point. When it does, they all should block and some I/O >>>>>> operation has to be performed by a single goroutine to renew the cached >>>>>> value, then unblock all other goroutines and have them use the new value. >>>>>> >>>>>> I solved this in the past in a number of ways: having a single goroutine >>>>>> that handles the cache by asking it for the value through a channel, >>>>>> using sync.Cond (which btw every time I decide to use I need to >>>>>> carefully re-read its docs and do lots of tests because I never get it >>>>>> right at first). But what I came to do lately is to implement an >>>>>> upgradable lock and have every goroutine do: >>>>> >>>>> >>>>> We have historically rejected this kind of adjustable lock. There is >>>>> some previous discussion at https://go.dev/issue/4026, >>>>> https://go.dev/issue/23513, https://go.dev/issue/38891, >>>>> https://go.dev/issue/44049. >>>>> >>>>> For a cache where checking that the cached value is valid (not stale) >>>>> and fetching the cached value is quick, then in general you will be >>>>> better off using a plain Mutex rather than RWMutex. RWMutex is more >>>>> complicated and therefore slower. It's only useful to use an RWMutex >>>>> when the read case is both contested and relatively slow. If the read >>>>> case is fast then the simpler Mutex will tend to be faster. And then >>>>> you don't have to worry about upgrading the lock. >>>>> >>>>> 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/CAOyqgcXNVFkc5H-L6K4Mt81gB6u91Ja07hob%3DS8Qwgy2buiQjQ%40mail.gmail.com. >>> >>> -- >>> 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/CAOyqgcWJ%2BLPOoTk9H7bxAj8_dLsuhgOpy_bZZrGW%3D%2Bz6N%3DrX-w%40mail.gmail.com. > > -- > 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/CAOyqgcVLzkTgiYqw%2BWh6pTFX74X-LYoyPFK5bkX7T8J8j3mb%3Dg%40mail.gmail.com. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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