Emilio G. Cota <c...@braap.org> writes:
> The meaning of "existing" is now changed to "matches in hash and
> ht->cmp result". This is saner than just checking the pointer value.
>
> Note that we now return NULL on insertion success, or the existing
> pointer on failure. We can do this because NULL pointers are not
> allowed to be inserted in QHT.
>
> Suggested-by: Richard Henderson <r...@twiddle.net>
> Signed-off-by: Emilio G. Cota <c...@braap.org>
> ---
> include/qemu/qht.h | 7 ++++---
> tests/qht-bench.c | 4 ++--
> tests/test-qht.c | 5 ++++-
> util/qht.c | 17 +++++++++--------
> 4 files changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/include/qemu/qht.h b/include/qemu/qht.h
> index dd512bf..c320cb6 100644
> --- a/include/qemu/qht.h
> +++ b/include/qemu/qht.h
> @@ -77,10 +77,11 @@ void qht_destroy(struct qht *ht);
> * In case of successful operation, smp_wmb() is implied before the pointer
> is
> * inserted into the hash table.
> *
> - * Returns true on success.
> - * Returns false if the @p-@hash pair already exists in the hash table.
> + * On success, returns NULL.
> + * On failure, returns the pointer from an entry that is equivalent (i.e.
> + * ht->cmp matches and the hash is the same) to @p-@h.
> */
> -bool qht_insert(struct qht *ht, void *p, uint32_t hash);
> +void *qht_insert(struct qht *ht, void *p, uint32_t hash);
Hmm this seems needlessly counter intuitive. I realise the potential
efficiency in overloading success/fail but wouldn't a:
bool qht_insert(struct qht *ht, void *p, uint32_t hash, void **existing);
be conceptually nicer?
>
> /**
> * qht_lookup_custom - Look up a pointer using a custom comparison function.
> diff --git a/tests/qht-bench.c b/tests/qht-bench.c
> index c94ac25..2f88400 100644
> --- a/tests/qht-bench.c
> +++ b/tests/qht-bench.c
> @@ -163,7 +163,7 @@ static void do_rw(struct thread_info *info)
> bool written = false;
>
> if (qht_lookup(&ht, p, hash) == NULL) {
> - written = qht_insert(&ht, p, hash);
> + written = !qht_insert(&ht, p, hash);
> }
> if (written) {
> stats->in++;
> @@ -322,7 +322,7 @@ static void htable_init(void)
> r = xorshift64star(r);
> p = &keys[r & (init_range - 1)];
> hash = h(*p);
> - if (qht_insert(&ht, p, hash)) {
> + if (qht_insert(&ht, p, hash) == NULL) {
> break;
> }
> retries++;
> diff --git a/tests/test-qht.c b/tests/test-qht.c
> index f8f2886..7164ae4 100644
> --- a/tests/test-qht.c
> +++ b/tests/test-qht.c
> @@ -27,11 +27,14 @@ static void insert(int a, int b)
>
> for (i = a; i < b; i++) {
> uint32_t hash;
> + void *existing;
>
> arr[i] = i;
> hash = i;
>
> - qht_insert(&ht, &arr[i], hash);
> + g_assert_true(!qht_insert(&ht, &arr[i], hash));
> + existing = qht_insert(&ht, &arr[i], hash);
> + g_assert_true(existing == &arr[i]);
> }
> }
>
> diff --git a/util/qht.c b/util/qht.c
> index dcb3ee1..f9f49a9 100644
> --- a/util/qht.c
> +++ b/util/qht.c
> @@ -511,9 +511,9 @@ void *qht_lookup(struct qht *ht, const void *userp,
> uint32_t hash)
> }
>
> /* call with head->lock held */
> -static bool qht_insert__locked(struct qht *ht, struct qht_map *map,
> - struct qht_bucket *head, void *p, uint32_t
> hash,
> - bool *needs_resize)
> +static void *qht_insert__locked(struct qht *ht, struct qht_map *map,
> + struct qht_bucket *head, void *p, uint32_t
> hash,
> + bool *needs_resize)
> {
> struct qht_bucket *b = head;
> struct qht_bucket *prev = NULL;
> @@ -523,8 +523,9 @@ static bool qht_insert__locked(struct qht *ht, struct
> qht_map *map,
> do {
> for (i = 0; i < QHT_BUCKET_ENTRIES; i++) {
> if (b->pointers[i]) {
> - if (unlikely(b->pointers[i] == p)) {
> - return false;
> + if (unlikely(b->hashes[i] == hash &&
> + ht->cmp(b->pointers[i], p))) {
> + return b->pointers[i];
> }
> } else {
> goto found;
> @@ -553,7 +554,7 @@ static bool qht_insert__locked(struct qht *ht, struct
> qht_map *map,
> atomic_set(&b->hashes[i], hash);
> atomic_set(&b->pointers[i], p);
> seqlock_write_end(&head->sequence);
> - return true;
> + return NULL;
> }
>
> static __attribute__((noinline)) void qht_grow_maybe(struct qht *ht)
> @@ -577,12 +578,12 @@ static __attribute__((noinline)) void
> qht_grow_maybe(struct qht *ht)
> qemu_mutex_unlock(&ht->lock);
> }
>
> -bool qht_insert(struct qht *ht, void *p, uint32_t hash)
> +void *qht_insert(struct qht *ht, void *p, uint32_t hash)
> {
> struct qht_bucket *b;
> struct qht_map *map;
> bool needs_resize = false;
> - bool ret;
> + void *ret;
>
> /* NULL pointers are not supported */
> qht_debug_assert(p);
--
Alex Bennée
