homework 11: implement tracing dfs func

[Ex4amp1e]

Finding with unstable test:

Even if the slice elements are on the heap, &heapPointerX for a local variable returns the address on the stack, which can different, and as result CI was getting different {{expectedPointers}} {{pointers}}.

The problem was that the address of a local stack variable was being taken, not the heap-allocated object.

Root cause:

var heapPointer1 = &heapObjects[1] is local func var on stack, even it is storing global heap addr. So it is stored on the func stack.
uintptr(unsafe.Pointer(&heapPointer1)) - it is actually taking addr of the func local var on stack,

Important: This address is not stable because:

• Go can move local variables around on the stack
• The stack can grow, causing variables to end up on different stack pages
• The stack may be allocated at different memory locations in CI versus local runs

Solution:

Solution is to use global variables or heap-allocated objects - then the uintptr values are always stable.

Error:

So, we can see pretty same right-side addresses, but different stack bytes (61 and 50)

=== RUN   TestTrace
    homework_test.go:78: 
        	Error Trace:	/home/runner/work/deep-go/deep-go/homeworks/11_garbage_collector/homework_test.go:78
        	Error:      	elements differ
        	            	
        	            	extra elements in list A:
        	            	([]interface {}) (len=8) {
        	            	 (uintptr) 0xc000061f08,
        	            	 (uintptr) 0xc000061ec0,
        	            	 (uintptr) 0xc000061f00,
        	            	 (uintptr) 0xc000061ec8,
        	            	 (uintptr) 0xc000061ed0,
        	            	 (uintptr) 0xc000061ef0,
        	            	 (uintptr) 0xc000061ef8,
        	            	 (uintptr) 0xc000061ed8
        	            	}
        	            	
        	            	
        	            	extra elements in list B:
        	            	([]interface {}) (len=8) {
        	            	 (uintptr) 0xc000050f08,
        	            	 (uintptr) 0xc000050ec8,
        	            	 (uintptr) 0xc000050ec0,
        	            	 (uintptr) 0xc000050f00,
        	            	 (uintptr) 0xc000050ed0,
        	            	 (uintptr) 0xc000050ef0,
        	            	 (uintptr) 0xc000050ef8,
        	            	 (uintptr) 0xc000050ed8
        	            	}
        	            	
        	            	
        	            	listA:
        	            	([]uintptr) (len=8) {
        	            	 (uintptr) 0xc000061f08,
        	            	 (uintptr) 0xc000061ec0,
        	            	 (uintptr) 0xc000061f00,
        	            	 (uintptr) 0xc000061ec8,
        	            	 (uintptr) 0xc000061ed0,
        	            	 (uintptr) 0xc000061ef0,
        	            	 (uintptr) 0xc000061ef8,
        	            	 (uintptr) 0xc000061ed8
        	            	}
        	            	
        	            	
        	            	listB:
        	            	([]uintptr) (len=8) {
        	            	 (uintptr) 0xc000050f08,
        	            	 (uintptr) 0xc000050ec8,
        	            	 (uintptr) 0xc000050ec0,
        	            	 (uintptr) 0xc000050f00,
        	            	 (uintptr) 0xc000050ed0,
        	            	 (uintptr) 0xc000050ef0,
        	            	 (uintptr) 0xc000050ef8,
        	            	 (uintptr) 0xc000050ed8
        	            	}
        	Test:       	TestTrace
--- FAIL: TestTrace (0.00s)