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 <javascript:>> > 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 <javascript:>. >> 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 <javascript:>* > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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