Add transaction counters to upper word of lockfree-stack head, to prevent ABA issues.

1 files changed, 17 insertions, 7 deletions

diff --git a/src/include/util/lockfree/stack.H b/src/include/util/lockfree/stack.H
index 8f884e072..a09c14ff9 100644
--- a/src/include/util/lockfree/stack.H
+++ b/src/include/util/lockfree/stack.H
@@ -23,11 +23,15 @@ namespace Util
 	template <typename _T>
 	_T* Stack<_T>::pop()
 	{
-	    _T * h = head;
-	    if (NULL == h) return h;
+	    _T * _head = head;
+	    _T * h = (_T*) (((uint64_t)_head) & 0x00000000FFFFFFFF);
+	    if (NULL == h) return h;	    
+	    uint64_t token = ((uint64_t)_head) >> 32;
+	    token++;
+	    _T * h_next = (_T*) (((uint64_t)(h->next)) | (token << 32));
 	    if (!__sync_bool_compare_and_swap(&head,
-					      h,
-					      h->next))
+					      _head,
+					      h_next))
 		return pop();
 	    return h;
 	}
@@ -35,10 +39,16 @@ namespace Util
 	template <typename _T>
 	void Stack<_T>::push(_T* p)
 	{
-	    p->next = head;
+	    _T* _head = head;
+	    p->next = (_T*) (((uint64_t)_head) & 0x00000000FFFFFFFF);
+	    uint64_t token = ((uint64_t)_head) >> 32;
+	    token++;
+
+	    _T* _p = (_T*) (((uint64_t)p) | (token << 32));
+	    	    
 	    if (!__sync_bool_compare_and_swap(&head,
-					      p->next,
-					      p))
+					      _head,
+					      _p))
 		push(p);
 	}
     }