From 97a5e3453abf63bbf5926979fcd89efb4388e937 Mon Sep 17 00:00:00 2001 From: Jonathan Nieder Date: Sun, 5 Dec 2010 03:35:17 -0600 Subject: [PATCH] treap: make treap_insert return inserted node Suppose I try the following: struct int_node *node = node_pointer(node_alloc(1)); node->n = 5; treap_insert(&root, node); printf("%d\n", node->n); Usually the result will be 5. But since treap_insert draws memory from the node pool, if the caller is unlucky then (1) the node pool will be full and (2) realloc will be forced to move the node pool to find room, so the node address becomes invalid and the result of dereferencing it is undefined. So we ought to use offsets in preference to pointers for references that would remain valid after a call to treap_insert. Tweak the signature to hint at a certain special case: since the inserted node can change address (though not offset), as a convenience teach treap_insert to return its new address. So the motivational example could be fixed by adding "node =". struct int_node *node = node_pointer(node_alloc(1)); node->n = 5; node = treap_insert(&root, node); printf("%d\n", node->n); Based on a true story. Signed-off-by: Jonathan Nieder Signed-off-by: Junio C Hamano --- test-treap.c | 11 ++++++++--- vcs-svn/trp.h | 3 ++- vcs-svn/trp.txt | 10 ++++++++-- 3 files changed, 18 insertions(+), 6 deletions(-) diff --git a/test-treap.c b/test-treap.c index cdba5111e1..ab8c951c6e 100644 --- a/test-treap.c +++ b/test-treap.c @@ -38,9 +38,14 @@ int main(int argc, char *argv[]) usage("test-treap < ints"); while (strbuf_getline(&sb, stdin, '\n') != EOF) { - item = node_alloc(1); - strtonode(node_pointer(item), sb.buf); - treap_insert(&root, node_pointer(item)); + struct int_node *node = node_pointer(node_alloc(1)); + + item = node_offset(node); + strtonode(node, sb.buf); + node = treap_insert(&root, node_pointer(item)); + if (node_offset(node) != item) + die("inserted %"PRIu32" in place of %"PRIu32"", + node_offset(node), item); } item = node_offset(treap_first(&root)); diff --git a/vcs-svn/trp.h b/vcs-svn/trp.h index ee35c688a0..c32b9184e9 100644 --- a/vcs-svn/trp.h +++ b/vcs-svn/trp.h @@ -188,11 +188,12 @@ a_attr uint32_t MAYBE_UNUSED a_pre##insert_recurse(uint32_t cur_node, uint32_t i return ret; \ } \ } \ -a_attr void MAYBE_UNUSED a_pre##insert(struct trp_root *treap, a_type *node) \ +a_attr a_type *MAYBE_UNUSED a_pre##insert(struct trp_root *treap, a_type *node) \ { \ uint32_t offset = trpn_offset(a_base, node); \ trp_node_new(a_base, a_field, offset); \ treap->trp_root = a_pre##insert_recurse(treap->trp_root, offset); \ + return trpn_pointer(a_base, offset); \ } \ a_attr uint32_t MAYBE_UNUSED a_pre##remove_recurse(uint32_t cur_node, uint32_t rem_node) \ { \ diff --git a/vcs-svn/trp.txt b/vcs-svn/trp.txt index eb4c191875..5ca6b42edb 100644 --- a/vcs-svn/trp.txt +++ b/vcs-svn/trp.txt @@ -21,7 +21,9 @@ The caller: . Allocates a `struct trp_root` variable and sets it to {~0}. -. Adds new nodes to the set using `foo_insert`. +. Adds new nodes to the set using `foo_insert`. Any pointers + to existing nodes cannot be relied upon any more, so the caller + might retrieve them anew with `foo_pointer`. . Can find a specific item in the set using `foo_search`. @@ -73,10 +75,14 @@ int (*cmp)(node_type \*a, node_type \*b) and returning a value less than, equal to, or greater than zero according to the result of comparison. -void foo_insert(struct trp_root *treap, node_type \*node):: +node_type {asterisk}foo_insert(struct trp_root *treap, node_type \*node):: Insert node into treap. If inserted multiple times, a node will appear in the treap multiple times. ++ +The return value is the address of the node within the treap, +which might differ from `node` if `pool_alloc` had to call +`realloc` to expand the pool. void foo_remove(struct trp_root *treap, node_type \*node)::