"Oh you've allocated a bit array for every value in the test range, then checked for gaps in it?"
Yes. What I should have said. (Though the test looks not for gaps but for two pigeons in one hole, but the same idea.) On Sun, Dec 1, 2019 at 8:44 PM Michael Jones <michael.jo...@gmail.com> wrote: > not necessary as the testing and updating is only done in one place by one > the main goroutine. > > On Sun, Dec 1, 2019 at 7:46 PM Robert Engels <reng...@ix.netcom.com> > wrote: > >> The updating of the bit array if shared needs to atomic as well, probably >> with a read and cas. >> >> On Dec 1, 2019, at 9:19 PM, Liam <networkimp...@gmail.com> wrote: >> >> >> Oh you've allocated a bit array for every value in the test range, then >> checked for gaps in it? >> >> On Sunday, December 1, 2019 at 2:21:55 PM UTC-8, Michael Jones wrote: >>> >>> Oh! That's just a bit per integer in the test range 0..total-1. Since Go >>> (and everything else) lacks a bit type, I just type such code >>> automatically. Bytes hold 8 bits. Array size must be rounded up, so >>> >>> a := make([]byte, (total+8-1)/8) >>> >>> array index for test integer n is n/8, so "n>>3" >>> >>> bit index for the j-th bit, counting up from 0 for the 1's place is >>> "1<<j" >>> >>> j is n%8, so "n&(8-1)" >>> >>> if mask=1<<(n&(8-1)) then one can test if the bit is set with >>> >>> a[n>>3] & mask != 0 >>> >>> to set it is >>> >>> a[n>>3] |= mask >>> >>> the values 3 and 8 here are from 8 bits in a byte and 8 = 2**3. if using >>> 64-bit ints they become 6 and 64. >>> >>> On Sat, Nov 30, 2019 at 7:06 PM Liam <networ...@gmail.com> wrote: >>> >>>> I wrote a less-sophisticated version of your test, then realized I'd >>>> misspent my time; all I needed was to change the atomic.Add*() to a >>>> mutex-protected counter, and see whether my app still failed; it did. >>>> >>>> But since you took the trouble, I read your code, and would like to >>>> understand your collision detector. Could you explain this bit? >>>> >>>> for _, v := range a { >>>> mask := byte(1 << (v & (8 - 1))) >>>> index := v >> 3 >>>> >>>> if tally[index]&mask != 0 { ... } >>>> ... >>>> } >>>> >>>> On Saturday, November 30, 2019 at 5:33:50 PM UTC-8, Michael Jones wrote: >>>>> >>>>> As a follow-up, some more timing: >>>>> >>>>> *47088064 atomic increments/sec (my original email above for heavy >>>>> synchronization conflict incrementing)* >>>>> >>>>> 142049067 atomic increments/sec when each goroutine has its own atomic >>>>> update target. (Not testing global synchronization/mutex, just the >>>>> overhead of congested vs not.) >>>>> >>>>> 426232527 ordinary "x++" increments in the workers. >>>>> >>>>> General idea to remember: >>>>> >>>>> Atomic increment is ~3x slower than simple add when uncontested. >>>>> Highly contested atomic increment is ~3x closer than uncontested, >>>>> therefore ~9x-10x slower than simple add. >>>>> >>>>> 10x is not insignificant, but is nevertheless remarkable for a >>>>> reliable atomic operation. This was once, "back in the day", a >>>>> remarkably expensive operation, an a feat of genius to accomplish >>>>> (Dekker's >>>>> Algorithm <https://en.wikipedia.org/wiki/Dekker%27s_algorithm>). That >>>>> it is now just a number-of-fingers cycles is fantastic progress! >>>>> >>>>> On Sat, Nov 30, 2019 at 3:38 PM Michael Jones <michae...@gmail.com> >>>>> wrote: >>>>> >>>>>> Liam, >>>>>> >>>>>> I just wrote a little stress test program for you. Maybe it will make >>>>>> you less stressed. ;-) >>>>>> https://play.golang.org/p/5_7Geyczd1V >>>>>> >>>>>> 4 CPU 2016 MacBook Pro: >>>>>> >>>>>> *celeste:atom mtj$ go run main.go* >>>>>> *32 concurrent workers* >>>>>> *128 batches of 1048576 atomic increments, 134217728 total increments* >>>>>> *2.850 seconds elapsed, 47088064 atomic increments/sec* >>>>>> *0 collisions* >>>>>> >>>>>> >>>>>> 18 CPU 2019 iMacPro: >>>>>> >>>>>> *plum:atom mtj$ go run main.go* >>>>>> *32 concurrent workers* >>>>>> *128 batches of 1048576 atomic increments, 134217728 total increments* >>>>>> *2.730 seconds elapsed, 49167382 atomic increments/sec* >>>>>> *0 collisions* >>>>>> >>>>>> >>>>>> Exhaustive demonstration is no proof, but changing the parameters >>>>>> here may increase your comfort. >>>>>> >>>>>> Michael >>>>>> >>>>>> On Sat, Nov 30, 2019 at 1:02 PM Robert Engels <ren...@ix.netcom.com> >>>>>> wrote: >>>>>> >>>>>>> If this was broken I think a lot of things would break. >>>>>>> >>>>>>> On Nov 30, 2019, at 1:56 PM, Liam <networ...@gmail.com> wrote: >>>>>>> >>>>>>> >>>>>>> The stress test for my app fails frequently with what looks like a >>>>>>> collision in atomic.AddUint64() results, so I wondered whether I had >>>>>>> misunderstood atomic-add. >>>>>>> >>>>>>> So far I can't reproduce it with a small program, so I've probably >>>>>>> misunderstood my app :-) >>>>>>> >>>>>>> On Friday, November 29, 2019 at 6:41:39 PM UTC-8, Kurtis Rader wrote: >>>>>>>> >>>>>>>> On Fri, Nov 29, 2019 at 6:21 PM Liam <networ...@gmail.com> wrote: >>>>>>>> >>>>>>>>> Does atomic.AddInt32(&x, 1) always yield unique values for >>>>>>>>> concurrent callers? >>>>>>>>> >>>>>>>>> I'm guessing not, because (I think) I'm seeing that two callers >>>>>>>>> get x+2, neither gets x+1. >>>>>>>>> >>>>>>>> >>>>>>>> That shouldn't happen, AFAICT. Can you share the code where the >>>>>>>> incorrect behavior is occurring? Or, preferably, a simple reproducer >>>>>>>> program? >>>>>>>> >>>>>>>> >>>>>>>>> Is there a way to generate unique values with pkg atomic, or is a >>>>>>>>> mutex required? >>>>>>>>> >>>>>>>> >>>>>>>> Keep in mind that atomic.AddInt32() has the usual two's-complement >>>>>>>> overflow semantics. If all you want is a generation counter you really >>>>>>>> should be using a uint32 and atomic.AddUint32(). Also, depending on >>>>>>>> your >>>>>>>> preferences and performance considerations you might find it >>>>>>>> preferable to >>>>>>>> use a channel that holds a single int, or small number of ints, that >>>>>>>> is fed >>>>>>>> by a producer goroutine and consumed by any context needing a uniq ID. >>>>>>>> That >>>>>>>> makes it easier to abstract the generation of "unique" ints so that >>>>>>>> they >>>>>>>> satisfy other constraints (e.g., they must be even, odd, prime, etc.). >>>>>>>> >>>>>>>> -- >>>>>>>> Kurtis Rader >>>>>>>> Caretaker of the exceptional canines Junior and Hank >>>>>>>> >>>>>>> -- >>>>>>> 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 golan...@googlegroups.com. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/golang-nuts/4f62dfff-6895-4aaa-9f0d-b635d5ba7ea7%40googlegroups.com >>>>>>> <https://groups.google.com/d/msgid/golang-nuts/4f62dfff-6895-4aaa-9f0d-b635d5ba7ea7%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>>> . >>>>>>> >>>>>>> -- >>>>>>> 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 golan...@googlegroups.com. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/golang-nuts/C7B99DEA-D183-44EF-9EDA-0B1841AB9DE5%40ix.netcom.com >>>>>>> <https://groups.google.com/d/msgid/golang-nuts/C7B99DEA-D183-44EF-9EDA-0B1841AB9DE5%40ix.netcom.com?utm_medium=email&utm_source=footer> >>>>>>> . >>>>>>> >>>>>> >>>>>> >>>>>> -- >>>>>> >>>>>> *Michael T. jonesmichae...@gmail.com* >>>>>> >>>>> >>>>> >>>>> -- >>>>> >>>>> *Michael T. jonesmichae...@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 golan...@googlegroups.com. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/golang-nuts/4d091a92-707a-40dc-8d1b-f12e10426438%40googlegroups.com >>>> <https://groups.google.com/d/msgid/golang-nuts/4d091a92-707a-40dc-8d1b-f12e10426438%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> >>> >>> -- >>> >>> *Michael T. jonesmichae...@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/4a457f1f-7956-474a-b29a-909aee0e55c3%40googlegroups.com >> <https://groups.google.com/d/msgid/golang-nuts/4a457f1f-7956-474a-b29a-909aee0e55c3%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> 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/4C46C912-25BB-459C-96DE-7D643F132757%40ix.netcom.com >> <https://groups.google.com/d/msgid/golang-nuts/4C46C912-25BB-459C-96DE-7D643F132757%40ix.netcom.com?utm_medium=email&utm_source=footer> >> . >> > > > -- > > *Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>* > -- *Michael T. jonesmichael.jo...@gmail.com <michael.jo...@gmail.com>* -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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