This currently has no users, but the use case is so common that I
think we must support it.
Note that without the appended we cannot safely remove a set of
elements; a 2-step approach (i.e. qht_iter first, keep track of
the to-be-deleted elements, and then a bunch of qht_remove calls)
would be racy, since between the iteration and the removals other
threads might insert additional elements.
Signed-off-by: Emilio G. Cota <c...@braap.org>
---
include/qemu/qht.h | 19 ++++++++++++
util/qht.c | 74 +++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 85 insertions(+), 8 deletions(-)
diff --git a/include/qemu/qht.h b/include/qemu/qht.h
index 1fb9116fa0..91bc9b00cf 100644
--- a/include/qemu/qht.h
+++ b/include/qemu/qht.h
@@ -44,6 +44,8 @@ struct qht_stats {
typedef bool (*qht_lookup_func_t)(const void *obj, const void *userp);
typedef void (*qht_iter_func_t)(struct qht *ht, void *p, uint32_t h, void *up);
+typedef bool (*qht_iter_bool_func_t)(struct qht *ht, void *p, uint32_t h,
+ void *up);
#define QHT_MODE_AUTO_RESIZE 0x1 /* auto-resize when heavily loaded */
@@ -178,9 +180,26 @@ bool qht_resize(struct qht *ht, size_t n_elems);
*
* Each time it is called, user-provided @func is passed a pointer-hash pair,
* plus @userp.
+ *
+ * Note: @ht cannot be accessed from @func
+ * See also: qht_iter_remove()
*/
void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp);
+/**
+ * qht_iter_remove - Iterate over a QHT, optionally removing entries
+ * @ht: QHT to be iterated over
+ * @func: function to be called for each entry in QHT
+ * @userp: additional pointer to be passed to @func
+ *
+ * Each time it is called, user-provided @func is passed a pointer-hash pair,
+ * plus @userp. If @func returns true, the pointer-hash pair is removed.
+ *
+ * Note: @ht cannot be accessed from @func
+ * See also: qht_iter()
+ */
+void qht_iter_remove(struct qht *ht, qht_iter_bool_func_t func, void *userp);
+
/**
* qht_statistics_init - Gather statistics from a QHT
* @ht: QHT to gather statistics from
diff --git a/util/qht.c b/util/qht.c
index 7b57b50a24..caec53dd0e 100644
--- a/util/qht.c
+++ b/util/qht.c
@@ -89,6 +89,19 @@
#define QHT_BUCKET_ENTRIES 4
#endif
+enum qht_iter_type {
+ QHT_ITER_VOID, /* do nothing; use retvoid */
+ QHT_ITER_RM, /* remove element if retbool returns true */
+};
+
+struct qht_iter {
+ union {
+ qht_iter_func_t retvoid;
+ qht_iter_bool_func_t retbool;
+ } f;
+ enum qht_iter_type type;
+};
+
/*
* Note: reading partially-updated pointers in @pointers could lead to
* segfaults. We thus access them with atomic_read/set; this guarantees
@@ -706,9 +719,10 @@ bool qht_remove(struct qht *ht, const void *p, uint32_t
hash)
return ret;
}
-static inline void qht_bucket_iter(struct qht *ht, struct qht_bucket *b,
- qht_iter_func_t func, void *userp)
+static inline void qht_bucket_iter(struct qht *ht, struct qht_bucket *head,
+ const struct qht_iter *iter, void *userp)
{
+ struct qht_bucket *b = head;
int i;
do {
@@ -716,7 +730,25 @@ static inline void qht_bucket_iter(struct qht *ht, struct
qht_bucket *b,
if (b->pointers[i] == NULL) {
return;
}
- func(ht, b->pointers[i], b->hashes[i], userp);
+ switch (iter->type) {
+ case QHT_ITER_VOID:
+ iter->f.retvoid(ht, b->pointers[i], b->hashes[i], userp);
+ break;
+ case QHT_ITER_RM:
+ if (iter->f.retbool(ht, b->pointers[i], b->hashes[i], userp)) {
+ /* replace i with the last valid element in the bucket */
+ seqlock_write_begin(&head->sequence);
+ qht_bucket_remove_entry(b, i);
+ seqlock_write_end(&head->sequence);
+ qht_bucket_debug__locked(b);
+ /* reevaluate i, since it just got replaced */
+ i--;
+ continue;
+ }
+ break;
+ default:
+ g_assert_not_reached();
+ }
}
b = b->next;
} while (b);
@@ -724,26 +756,48 @@ static inline void qht_bucket_iter(struct qht *ht, struct
qht_bucket *b,
/* call with all of the map's locks held */
static inline void qht_map_iter__all_locked(struct qht *ht, struct qht_map
*map,
- qht_iter_func_t func, void *userp)
+ const struct qht_iter *iter,
+ void *userp)
{
size_t i;
for (i = 0; i < map->n_buckets; i++) {
- qht_bucket_iter(ht, &map->buckets[i], func, userp);
+ qht_bucket_iter(ht, &map->buckets[i], iter, userp);
}
}
-void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp)
+static inline void
+do_qht_iter(struct qht *ht, const struct qht_iter *iter, void *userp)
{
struct qht_map *map;
map = atomic_rcu_read(&ht->map);
qht_map_lock_buckets(map);
/* Note: ht here is merely for carrying ht->mode; ht->map won't be read */
- qht_map_iter__all_locked(ht, map, func, userp);
+ qht_map_iter__all_locked(ht, map, iter, userp);
qht_map_unlock_buckets(map);
}
+void qht_iter(struct qht *ht, qht_iter_func_t func, void *userp)
+{
+ const struct qht_iter iter = {
+ .f.retvoid = func,
+ .type = QHT_ITER_VOID,
+ };
+
+ do_qht_iter(ht, &iter, userp);
+}
+
+void qht_iter_remove(struct qht *ht, qht_iter_bool_func_t func, void *userp)
+{
+ const struct qht_iter iter = {
+ .f.retbool = func,
+ .type = QHT_ITER_RM,
+ };
+
+ do_qht_iter(ht, &iter, userp);
+}
+
static void qht_map_copy(struct qht *ht, void *p, uint32_t hash, void *userp)
{
struct qht_map *new = userp;
@@ -760,6 +814,10 @@ static void qht_map_copy(struct qht *ht, void *p, uint32_t
hash, void *userp)
static void qht_do_resize_reset(struct qht *ht, struct qht_map *new, bool
reset)
{
struct qht_map *old;
+ const struct qht_iter iter = {
+ .f.retvoid = qht_map_copy,
+ .type = QHT_ITER_VOID,
+ };
old = ht->map;
qht_map_lock_buckets(old);
@@ -774,7 +832,7 @@ static void qht_do_resize_reset(struct qht *ht, struct
qht_map *new, bool reset)
}
g_assert(new->n_buckets != old->n_buckets);
- qht_map_iter__all_locked(ht, old, qht_map_copy, new);
+ qht_map_iter__all_locked(ht, old, &iter, new);
qht_map_debug__all_locked(new);
atomic_rcu_set(&ht->map, new);
--
2.17.1
