On Thu, Jan 24, 2019 at 11:58 PM <mountain...@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+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
