It is in line 899 and line 914 of the malloc.go file.
899 spc := makeSpanClass(sizeclass, noscan)
914 s = largeAlloc(size, needzero, noscan)
在 2019年1月27日星期日 UTC+8下午1:55:29，Ian Lance Taylor写道：
>
> On Sat, Jan 26, 2019 at 6:50 PM <mount...@gmail.com <javascript:>> wrote:
> >
> > I am looking at go1.11.1.
>
> I don't see a "noscan" flag for mallocgc in 1.11.1. There is a noscan
> local variable, which is set of the type is passed as nil (the case I
> mentioned earlier) or if the type has no pointers.
>
> > The memory allocation is still difficult to understand. What reference
> materials can help me understand the context of this block?
>
> There is some information at golang.org/s/go14gc but I'm not sure it
> quite covers what you are looking for.
>
> Ian
>
>
> > 在 2019年1月27日星期日 UTC+8上午3:03:47，Ian Lance Taylor写道：
> >>
> >> On Sat, Jan 26, 2019 at 5:37 AM <mount...@gmail.com> wrote:
> >> >
> >> > Why the garbage collector won't know how to find the pointers?
> >> > I looked at mallocgc and decided if the GC needs to scan this object
> based on the noscan flag.
> >>
> >> What version of Go are you looking at? There was a flagNoScan as late
> >> as Go 1.6, but there is no such flag in current versions of Go.
> >>
> >> Ian
> >>
> >> > 在 2019年1月25日星期五 UTC+8下午10:58:44，Ian Lance Taylor写道：
> >> >>
> >> >> On Thu, Jan 24, 2019 at 11:58 PM <mount...@gmail.com> wrote:
> >> >> >
> >> >> > go 1.11.1 source code is below:
> >> >> >
> >> >> > Generally speaking, make chan just pay attention to the presence
> or absence of buf.
> >> >> >
> >> >> > When I saw the source code of make chan, I can understand case 1:
> chan buf is 0, but can't understand case 2 & default.
> >> >> >
> >> >> > Who knows this principle?
> >> >> >
> >> >> > Thanks!
> >> >> >
> >> >> > var c *hchan
> >> >> > switch {
> >> >> > case size == 0 || elem.size == 0:
> >> >> > // Queue or element size is zero.
> >> >> > c = (*hchan)(mallocgc(hchanSize, nil, true))
> >> >> > // Race detector uses this location for synchronization.
> >> >> > c.buf = c.raceaddr()
> >> >> > case elem.kind&kindNoPointers != 0:
> >> >> > // Elements do not contain pointers.
> >> >> > // Allocate hchan and buf in one call.
> >> >> > c = (*hchan)(mallocgc(hchanSize+uintptr(size)*elem.size,
> nil, true))
> >> >> > c.buf = add(unsafe.Pointer(c), hchanSize)
> >> >> > default:
> >> >> > // Elements contain pointers.
> >> >> > c = new(hchan)
> >> >> > c.buf = mallocgc(uintptr(size)*elem.size, elem, true)
> >> >> > }
> >> >>
> >> >>
> >> >> First, let me say: please don't post screen shots. They are much
> >> >> harder to read than ordinary text. I don't understand why anybody
> >> >> ever posts screenshots of code, and I would be grateful for an
> >> >> explanation. Thanks.
> >> >>
> >> >> What is happening in that code is that if the channel has a non-zero
> >> >> buffer size, we need to allocate space to hold the elements in the
> >> >> buffer. If the elements in the buffer do not contain any pointers,
> we
> >> >> can optimize by allocating the channel structure (hchan) and the
> >> >> buffer in a single memory allocation. If the elements do contain
> >> >> pointers, then that won't work, because the garbage collector won't
> >> >> know how to find the pointers. So in that case we allocate the
> hchan
> >> >> struct and the buffer separately. Note the second argument to
> >> >> mallocgc, which is the type of the memory being allocated. When
> there
> >> >> are no pointers, we pass nil, which tells the garbage collector that
> >> >> the allocation contains no pointers. In the pointer case, we pass
> the
> >> >> element type.
> >> >>
> >> >> 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...@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...@googlegroups.com <javascript:>.
> > 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.
