Emilio G. Cota <c...@braap.org> writes:
> 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
I'm confused by this comment. If @ht cannot be accessed (or shouldn't be
accessed) from @func then why are we passing it?
> + * 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);
Otherwise:
Reviewed-by: Alex Bennée <alex.ben...@linaro.org>
--
Alex Bennée
