So far, all the users of the decoration API used decoration that
only grows and discarded at the end of the program execution.

Introduce for_each_decoration() that lets the caller iterate over
all defined decorations and use it to implement clear_decoration()

Signed-off-by: Junio C Hamano <>
 Documentation/technical/api-decorate.txt | 22 ++++++++++++++++++++++
 decorate.c                               | 19 +++++++++++++++++++
 decorate.h                               |  4 ++++
 3 files changed, 45 insertions(+)

diff --git a/Documentation/technical/api-decorate.txt 
index 0cc2b64..600366d 100644
--- a/Documentation/technical/api-decorate.txt
+++ b/Documentation/technical/api-decorate.txt
@@ -35,3 +35,25 @@ the `obj`.  You cannot tell if `obj` does not appear in the 
 at all, or if `obj` has decoration whose value is NULL, so if you want
 to use the decoration API for "Did I see this object?" hashtable,
 use decoration value that is _not_ NULL.
+`for_each_decoration(struct decoration *deco, for_each_decoration_fn fn)`
+iterates over all the entries in the hashtable, and calls `fn` on each
+entry.  The `fn` callback function takes a single `struct object_decoration`
+as its parameter, that has `base` field that points at the `obj`
+given to an earlier call to `add_decoration` and `decoration` field
+that remembers the `decoration`.
+`clear_decoration(struct decoration *deco, for_each_decoration_fn fn)`,
+when `fn` is not NULL, iterates over all the entries and calls the
+callback function `fn` using `for_each_decoration`, and then frees
+the memory used for the hashtable but not the `struct decoration` itself.
+The callback function can be used to release the resource used by
+the `decoration` the earlier `add_decoration` registered to the
diff --git a/decorate.c b/decorate.c
index 2f8a63e..3e15358 100644
--- a/decorate.c
+++ b/decorate.c
@@ -86,3 +86,22 @@ void *lookup_decoration(struct decoration *n, const struct 
object *obj)
                        j = 0;
+void for_each_decoration(struct decoration *n, for_each_decoration_fn fn)
+       int i;
+       for (i = 0; i < n->size; i++) {
+               struct object_decoration *entry = &n->hash[i];
+               if (!entry->base)
+                       continue;
+               fn(entry);
+       }
+void clear_decoration(struct decoration *n, for_each_decoration_fn fn)
+       if (fn)
+               for_each_decoration(n, fn);
+       free(n->hash);
diff --git a/decorate.h b/decorate.h
index e732804..4a0d37e 100644
--- a/decorate.h
+++ b/decorate.h
@@ -15,4 +15,8 @@ struct decoration {
 extern void *add_decoration(struct decoration *n, const struct object *obj, 
void *decoration);
 extern void *lookup_decoration(struct decoration *n, const struct object *obj);
+typedef void (*for_each_decoration_fn)(struct object_decoration *);
+extern void for_each_decoration(struct decoration *, for_each_decoration_fn);
+extern void clear_decoration(struct decoration *, for_each_decoration_fn);

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