Avoid cgo bug by use C.calloc to allocate memory in C instead of C.ma…

[waldoweng]

…lloc,

See https://pkg.go.dev/cmd/cgo:

Note: the current implementation has a bug. While Go code is permitted to write nil or a C pointer (but not a Go pointer) to C memory, the current implementation may sometimes cause a runtime error if the contents of the C memory appear to be a Go pointer. Therefore, avoid passing uninitialized C memory to Go code if the Go code is going to store pointer values in it. Zero out the memory in C before passing it to Go.

I also find similar approach use by Dgraph according to this blog post:
https://dgraph.io/blog/post/manual-memory-management-golang-jemalloc/

So, instead of using malloc, we use its slightly more expensive sibling, calloc. calloc works the same way as malloc, except it zeroes out the memory before returning it to the caller.

[f41gh7]

Hello, do you have any examples with panic related to this lib?

As far as I understand current issue with CGO. It's only possible to get a panic, if program makes allocation of uninitialized objects via malloc and shadows it with GO allocations. Usual example for it is slice resizing via append.

[f41gh7]

Related issue golang/go#19928

[valyala]

@waldoweng , thanks for the fix!