// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Lock-free stack.
// Initialize head to 0, compare with 0 to test for emptiness.
// The stack does not keep pointers to nodes,
// so they can be garbage collected if there are no other pointers to nodes.
// The following code runs only in non-preemptible contexts.

package runtime

import (
	"runtime/internal/atomic"
	"unsafe"
)

// Temporary for C code to call:
//go:linkname lfstackpush runtime.lfstackpush
//go:linkname lfstackpop runtime.lfstackpop

func lfstackpush(head *uint64, node *lfnode) {
	node.pushcnt++
	new := lfstackPack(node, node.pushcnt)
	if node1 := lfstackUnpack(new); node1 != node {
		print("runtime: lfstackpush invalid packing: node=", node, " cnt=", hex(node.pushcnt), " packed=", hex(new), " -> node=", node1, "\n")
		throw("lfstackpush")
	}
	for {
		old := atomic.Load64(head)
		node.next = old
		if atomic.Cas64(head, old, new) {
			break
		}
	}
}

func lfstackpop(head *uint64) unsafe.Pointer {
	for {
		old := atomic.Load64(head)
		if old == 0 {
			return nil
		}
		node := lfstackUnpack(old)
		next := atomic.Load64(&node.next)
		if atomic.Cas64(head, old, next) {
			return unsafe.Pointer(node)
		}
	}
}