Reduce empty BTree memory requirements

Avoid over-allocating the ZixBTree structure, and only allocate a root node
when elements are inserted. The over-allocation was to make all allocations use
pages (towards disk-backed storage), but since this isn't actually supported at
the moment it was just a waste of memory.

1 files changed, 18 insertions, 0 deletions

diff --git a/test/test_btree.c b/test/test_btree.c
index dd665c7..a87e26e 100644
--- a/test/test_btree.c
+++ b/test/test_btree.c
@@ -101,6 +101,23 @@ destroy(void* const ptr, const void* const user_data)
 }
 
 static void
+test_empty(void)
+{
+  ZixBTree* const t = zix_btree_new(NULL, int_cmp, NULL);
+  assert(t);
+
+  // Check that reading functions work properly with an empty (rootless) tree
+  const int    e  = 42;
+  ZixBTreeIter ti = zix_btree_end(t);
+  zix_btree_clear(t, NULL, NULL);
+  assert(!zix_btree_size(t));
+  assert(zix_btree_find(t, &e, &ti) == ZIX_STATUS_NOT_FOUND);
+  assert(!zix_btree_lower_bound(t, int_cmp, NULL, &e, &ti));
+
+  zix_btree_free(t, destroy, NULL);
+}
+
+static void
 test_clear(void)
 {
   ZixBTree* t = zix_btree_new(NULL, int_cmp, NULL);
@@ -576,6 +593,7 @@ main(int argc, char** argv)
     return EXIT_FAILURE;
   }
 
+  test_empty();
   test_clear();
   test_free();
   test_iter_comparison();