GHash: ensure function, avoids multiple lookups

2 files changed, 47 insertions, 0 deletions

diff --git a/source/blender/blenlib/BLI_ghash.h b/source/blender/blenlib/BLI_ghash.h
index 16d18ef1315..a00ddeefb2b 100644
--- a/source/blender/blenlib/BLI_ghash.h
+++ b/source/blender/blenlib/BLI_ghash.h
@@ -79,6 +79,7 @@ bool   BLI_ghash_reinsert(GHash *gh, void *key, void *val, GHashKeyFreeFP keyfre
 void  *BLI_ghash_lookup(GHash *gh, const void *key) ATTR_WARN_UNUSED_RESULT;
 void  *BLI_ghash_lookup_default(GHash *gh, const void *key, void *val_default) ATTR_WARN_UNUSED_RESULT;
 void **BLI_ghash_lookup_p(GHash *gh, const void *key) ATTR_WARN_UNUSED_RESULT;
+bool   BLI_ghash_ensure_p(GHash *gh, void *key, void ***r_val) ATTR_WARN_UNUSED_RESULT;
 bool   BLI_ghash_remove(GHash *gh, void *key, GHashKeyFreeFP keyfreefp, GHashValFreeFP valfreefp);
 void   BLI_ghash_clear(GHash *gh, GHashKeyFreeFP keyfreefp, GHashValFreeFP valfreefp);
 void   BLI_ghash_clear_ex(GHash *gh, GHashKeyFreeFP keyfreefp, GHashValFreeFP valfreefp,
diff --git a/source/blender/blenlib/intern/BLI_ghash.c b/source/blender/blenlib/intern/BLI_ghash.c
index 11848804194..dae7af6a927 100644
--- a/source/blender/blenlib/intern/BLI_ghash.c
+++ b/source/blender/blenlib/intern/BLI_ghash.c
@@ -445,6 +445,22 @@ BLI_INLINE void ghash_insert_ex(
 }
 
 /**
+ * Insert function that takes a pre-allocated entry.
+ */
+BLI_INLINE void ghash_insert_ex_keyonly_entry(
+        GHash *gh, void *key, const unsigned int bucket_index,
+        Entry *e)
+{
+	BLI_assert((gh->flag & GHASH_FLAG_ALLOW_DUPES) || (BLI_ghash_haskey(gh, key) == 0));
+
+	e->next = gh->buckets[bucket_index];
+	e->key = key;
+	gh->buckets[bucket_index] = e;
+
+	ghash_buckets_expand(gh, ++gh->nentries, false);
+}
+
+/**
  * Insert function that doesn't set the value (use for GSet)
  */
 BLI_INLINE void ghash_insert_ex_keyonly(
@@ -721,6 +737,36 @@ void **BLI_ghash_lookup_p(GHash *gh, const void *key)
 }
 
 /**
+ * Ensure \a key is exists in \a gh.
+ *
+ * This handles the common situation where the caller needs ensure a key is added to \a gh,
+ * constructing a new value in the case the key isn't found.
+ * Otherwise use the existing value.
+ *
+ * Such situations typically incur multiple lookups, however this function
+ * avoids them by ensuring the key is added,
+ * returning a pointer to the value so it can be used or initialized by the caller.
+ *
+ * \returns true when the value didn't need to be added.
+ * (when false, the caller _must_ initialize the value).
+ */
+bool BLI_ghash_ensure_p(GHash *gh, void *key, void ***r_val)
+{
+	const unsigned int hash = ghash_keyhash(gh, key);
+	const unsigned int bucket_index = ghash_bucket_index(gh, hash);
+	GHashEntry *e = (GHashEntry *)ghash_lookup_entry_ex(gh, key, bucket_index);
+	const bool haskey = (e != NULL);
+
+	if (!haskey) {
+		e = BLI_mempool_alloc(gh->entrypool);
+		ghash_insert_ex_keyonly_entry(gh, key, bucket_index, (Entry *)e);
+	}
+
+	*r_val = &e->val;
+	return haskey;
+}
+
+/**
  * Remove \a key from \a gh, or return false if the key wasn't found.
  *
  * \param key  The key to remove.