is it safe in golang 1.17 to change the pointer receiver's value with atomic swap pointer

Question

golang 1.17 changed from stack to register to handle the params

is it safe when i use atomic.SwapPointer to change the pointer receiver's value

below is the code

//like this
func (this *A) Replace(a *A) {
    //other business logic
    //....
    //business logic end
    atomic.SwapPointer((*unsafe.Pointer)(unsafe.Pointer(&this)), unsafe.Pointer(a))
}

On a side note, it is recommended *not* to name your method receivers things like `this` or `self`. — Adrian, Aug 31 '21 at 14:31
It's not only unsafe, it's also useless. It accomplishes nothing. — torek, Aug 31 '21 at 14:53

score 0 · Answer 1 · answered Aug 31 '21 at 14:26

0

[I]s it safe in golang 1.17 to change the pointer receiver's value with atomic swap pointer [?]

No. Use of package unsafe is unsafe by definition of unsafe.

("safe" in which sense?)

answered Aug 31 '21 at 14:26

Volker

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Unsafe it is for any definition of safe. – Volker Aug 31 '21 at 14:54
3

Is this really an answer? this could simply be a comment – gold_cy Aug 31 '21 at 15:14

score 0 · Answer 2 · answered Aug 31 '21 at 21:29

I don't think this is doing what you want it to. From the point-of-view of Go code, even "sensible" unsafe code, you cannot tell the difference between the register and stack ABI. If you take the address of a parameter, if it was not already in memory, it will be stored to memory, and that will be its address. If that address is passed to a function that "escapes" the address by storing it in a global or in the heap, then the memory for the parameter will actually be obtained by heap-allocating a slot for it and storing it there. If this happens, then subsequent reference to the parameter will indirect through the hidden pointer to its heap address.

is it safe in golang 1.17 to change the pointer receiver's value with atomic swap pointer

2 Answers2