On Wednesday, March 22, 2017 at 4:56:28 PM UTC+8, Dave Cheney wrote: > > The comment on > > https://github.com/golang/go/blob/master/src/runtime/mgc.go#L47 > > // c. GC performs root marking jobs. This includes scanning all > // stacks, shading all globals, and shading any heap pointers in > // off-heap runtime data structures. Scanning a stack stops a > // goroutine, shades any pointers found on its stack, and then > // resumes the goroutine. >
> Suggests there are a few runtime internal data structures. > Thanks for the link. I was just curious on where heap pointers of local allocated memory blocks are stored. So there is the third kind of root, off-heap runtime data structures, to store heap pointers of local allocated memory blocks. > But from the POV of a programmer, it's globals, and things reachable from > each goroutine's stack. > More accurately, I think it should be: from the POV of a programmer, it's globals, and things reachable from each goroutine. > On Wednesday, 22 March 2017 19:51:40 UTC+11, T L wrote: >> >> >> >> On Wednesday, March 22, 2017 at 4:33:21 PM UTC+8, Dave Cheney wrote: >>> >>> >>> >>> On Wednesday, 22 March 2017 19:29:02 UTC+11, T L wrote: >>>> >>>> >>>> >>>> On Wednesday, March 22, 2017 at 4:08:02 PM UTC+8, Dave Cheney wrote: >>>>> >>>>> >>>>> >>>>> On Wednesday, 22 March 2017 19:04:36 UTC+11, T L wrote: >>>>>> >>>>>> In this article: https://blog.golang.org/go15gc , it mentions >>>>>> >>>>>> ..., The GC visits all *roots*, which are objects directly >>>>>>> accessible by the application such as globals and things on the stack, >>>>>>> and >>>>>>> colors these grey. ... >>>>>> >>>>>> >>>>>> It lists two kinds of root objects: globals and objects on stacks. >>>>>> My question is how objects on heap will be visited? >>>>>> >>>>> >>>>> By walking the heap (there are some optimisations to avoid areas of >>>>> memory where no objects are known to be stored) >>>>> >>>> >>>> Walking the heap is at collecting stage? Will the heap be walked at >>>> analyzing stage? >>>> >>> >>> Garbage collection has two main phases; mark and sweep. The heap is >>> walked during the marking phase. >>> >>>> >>>> >>>>> >>>>> >>>>>> For every object on heap, is it always been referenced by another >>>>>> global object or another object on a stack? >>>>>> >>>>> >>>>> Yes, otherwise it's garbage :) >>>>> >>>> >>>> >>> So when a memory block for a local object is allocated on heap, there >>>> will be also a pointer, which stores the address of the memory block, >>>> recorded on stack? >>>> >>> >>> When memory is allocated on the heap, memory is allocated on the heap; >>> that's it. The garbage collector records the details of the type of the >>> allocation in the heap alongside the object for most* allocations. >>> >>> * for small allocations they go into their own areas; google slab >>> allocator. >>> >>> So that the memory block on heap will be tracked from stack? >>>> >>> >>> From any gc root. The point is if there is no path from a gc root to an >>> area of memory on the heap, that area is unreachable and therefore can be >>> reused. >>> >> >> except globals and stack objects, are there any other roots? >> >> >>> >>> >>>> >>>> >>> -- 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.
