RFR: Implement JEP 509: JFR CPU-Time Profiling [v45]

[Johan Sjölen]

On Mon, 5 May 2025 13:17:31 GMT, Johan Sjölen <jsjolen at openjdk.org> wrote:

>> I see. If it is only used in signal handlers, does it really need to be multi-threaded?
>
> The `LockFreeStack` doesn't say how its elements are allocated, so you can allocate your elements into an array.

```c++
struct Node { volatile Node* next; int x; static volatile Node* get_next(Node& n)  { return n->next; } }
static Node nodes[16];
static i = 0;
Node* alloc() {
  return nodes[i++]:
}

void foo() {
  LockFreeStack<Node, Node::get_next> lfs;
  Node* n = alloc();
  n->x = 0;
  lfs.push(n*);
  Node* n2 = lfs.top();
  tty->print_cr("%d\n", n2->x);
  lfs.pop();
}

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PR Review Comment: https://git.openjdk.org/jdk/pull/20752#discussion_r2073436807