From 69d55e9cc28dc2f1e2f2426d2a43f2d10db76f29 Mon Sep 17 00:00:00 2001 From: "Emilio G. Cota" Date: Wed, 15 Aug 2018 15:00:48 -0400 Subject: [PATCH] qht: add qht_iter_remove MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Reviewed-by: Alex Bennée Signed-off-by: Emilio G. Cota Signed-off-by: Richard Henderson --- 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 c9a11cc29a..3a9618db69 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 */ #define QHT_MODE_RAW_MUTEXES 0x2 /* bypass the profiler (QSP) */ @@ -179,9 +181,26 @@ 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 28d9273371..c190e89f5b 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; +}; + /* * Do _not_ use qemu_mutex_[try]lock directly! Use these macros, otherwise * the profiler (QSP) will deadlock. @@ -733,9 +746,10 @@ 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 { @@ -743,7 +757,25 @@ 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); @@ -751,26 +783,48 @@ 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; @@ -787,6 +841,10 @@ 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); @@ -801,7 +859,7 @@ 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);