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qht: add qht_iter_remove 

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 <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Emilio G. Cota 2018-08-15 15:00:48 -04:00 committed by Richard Henderson
parent e2f07efadd
commit 69d55e9cc2
2 changed files with 85 additions and 8 deletions
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19
include/qemu/qht.h
View File

@ -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

74
util/qht.c
View File

@ -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);