Presentation by Philip W. Howard. Paper and more information: http://soft.vub.ac.be/races/paper/the-case-for-relativistic-programming/

1. 10/21/2012 Races'12
A Case for Relativistic
Programming
Philip W. Howard
West Virginia University Institute of Technology
Jonathan Walpole
Portland State University

2. 10/21/2012 Races'12 2
Events
E1
E2
O1
O2

3. 10/21/2012 Races'12 3
Triangle inequality: a + b >= c
E1
E2
O2
a
c
b
Causality

4. 10/21/2012 Races'12 4
Causalty in Computers
• If computers were just wires, we’d be OK
• Computers are wires + illogic

5. 10/21/2012 Races'12 5
illogic example
A B D
C
C = malloc();
C->data = data;
C->next = D;
B->next = C;
rp-publish(B->next, C);

6. 10/21/2012 Races'12 6
Need for causal delays
A B D
CC
B->next = D;
wait-for-readers();
free(C);

7. 10/21/2012 Races'12 7
Rules for Placing Relativistic
Programming Primitives
1. Write globally visible pointers with
rp_publish()
2. When performing two writes, one earlier
in traversal order and one later in
traversal order, separate the two with
wait-for-readers()

8. 10/21/2012 Races'12 8
Relativistic vs. Concurrent
Balanced Trees
•Relativistic Red Black Trees
•Concurrent AVL Trees
A practical concurrent binary search tree.
PPoPP ’10; Bronson et al

9. 10/21/2012 Races'12 9
Concurrent AVL get
20 V get(K k) {
21 return (V)attemptGet(k, rootHolder, 1, 0);
22 }
23
24 Object attemptGet(
25 K k, Node node, int dir, long nodeV) {
26 while (true) {
27 Node child = node.child(dir);
28 if (((node.version^nodeV) & IgnoreGrow) != 0)
29 return Retry;
30 if (child == null)
31 return null;
32 int nextD = k.compareTo(child.key);
33 if (nextD == 0)
34 return child.value;
35 long chV = child.version;
36 if ((chV & Shrinking) != 0) {
37 waitUntilNotChanging(child);
38 } else if (chV != Unlinked &&
39 child == node.child(dir)) {
40 if (((node.version^nodeV) & IgnoreGrow) != 0)
41 return Retry;
42 Object p = attemptGet(k, child, nextD, chV);
43 if (p != Retry)

10. 10/21/2012 Races'12 10
Relativistic RBTree Get
void *rb_find(rbtree *tree, long key)
{
void *value;
rbnode_t *node = tree->root;
start_read();
while (node != NULL) {
if (key == node->key)
break;
else if (key < node->key)
node = rp-dereference(node->left);
else
node = rp-dereference(node->right);
}
if (node != NULL)
value = node->value;
else
value = NULL;

11. 10/21/2012 Races'12 11
RBTree Delete

12. 10/21/2012 Races'12 12
RP Delete
rbnode_t *new_node = rbnode_copy(swap);
rp-publish(new_node->left, node->left);
node->left->parent = new_node;
rp-publish(new_node->right, node->right);
node->right->parent = new_node;
if (is_left(node))
rp-publish(prev->left, new_node);
else
rp-publish (prev->right, new_node);
new_node->parent = prev;
// need to make sure new_node is seen before path to b is erased
wait-for-readers(tree->lock);
prev = swap->parent;
next = swap->right;
rp-publish(prev->left, swap->right);
if (swap->right != NULL) swap->right->parent = prev;

13. 10/21/2012 Races'12 13
0
7500000
15000000
22500000
30000000
0 18 35 53 70
Read Performance
Reads/Sec
Read Threads
NOLOCK reads
NOLOCK cont. reads
RP reads
RP cont. reads
ccavl reads
ccavl cont. reads

14. 10/21/2012 Races'12 14
0
50000
100000
150000
200000
0 18 35 53 70
Contended Write Performance
Writes/sec
Read Threads
NOLOCK writes
RP writes
ccavl writes

15. 10/21/2012 Races'12 15
Benefits of RP
• High performance, Highly scalable reads
• Simple Code
• Strong correctness properties