I am looking at go1.11.1.
The memory allocation is still difficult to understand. What reference
materials can help me understand the context of this block?
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 <javascript:>> 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
> >
> > --
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