avoid dups with lock-free insert

f484e1cb · Nickolai Zeldovich · 3bc01fa3 · f484e1cb · f484e1cb · f484e1cb
--- a/defs.h
+++ b/defs.h
@@ -100,7 +100,7 @@ void            mpstartthem(void);

 // ns.c
 void            nsinit(void);
-struct ns*      nsalloc(void);
+struct ns*      nsalloc(int allowdup);
 int             ns_allockey(struct ns*);
 int             ns_insert(struct ns*, int key, void*);
 void*           ns_lookup(struct ns*, int);

--- a/ns.c
+++ b/ns.c
@@ -24,7 +24,7 @@ struct bucket {
 } __attribute__((aligned (CACHELINE)));

 struct ns {
-  int used;
+  int allowdup;
  int nextkey;
  struct bucket table[NHASH];
 };
@@ -36,7 +36,7 @@ nsinit(void)

 // XXX should be using our missing scalable allocator module
 struct ns*
-nsalloc(void)
+nsalloc(int allowdup)
 {
  struct ns *ns = 0;

@@ -45,6 +45,7 @@ nsalloc(void)
    panic("nsalloc");
  memset(ns, 0, sizeof(struct ns));
  ns->nextkey = 1;
+  ns->allowdup = allowdup;
  return ns;
 }

@@ -70,23 +71,34 @@ ns_allockey(struct ns *ns)
 int 
 ns_insert(struct ns *ns, int key, void *val) 
 {
-  int r = -1;
  struct elem *e = elemalloc();
  if (e) {
    e->key = key;
    e->val = val;
    uint i = key % NHASH;
    rcu_begin_write(0);
-    for (;;) {
-      struct elem *x = ns->table[i].chain;
-      e->next = x;
-      if (__sync_bool_compare_and_swap(&ns->table[i].chain, x, e))
-	break;
+
+   retry:
+    (void) 0;
+    struct elem *root = ns->table[i].chain;
+    if (!ns->allowdup) {
+      for (struct elem *x = root; x; x = x->next) {
+	if (x->key == key) {
+	  rcu_end_write(0);
+	  rcu_delayed(e, kmfree);
+	  return -1;
+	}
+      }
    }
+
+    e->next = root;
+    if (!__sync_bool_compare_and_swap(&ns->table[i].chain, root, e))
+      goto retry;
+
    rcu_end_write(0);
-    r = 0;
+    return 0;
  }
-  return r;
+  return -1;
 }

 void*

--- a/proc.c
+++ b/proc.c
@@ -25,11 +25,11 @@ pinit(void)
 {
  int c;

-  nspid = nsalloc();
+  nspid = nsalloc(0);
  if (nspid == 0)
    panic("pinit");

-  nsrunq = nsalloc();
+  nsrunq = nsalloc(1);
  if (nsrunq == 0)
    panic("pinit runq");