From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39980) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fyI6R-0007CP-Qo for qemu-devel@nongnu.org; Fri, 07 Sep 2018 10:51:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fyI6N-0007n7-AI for qemu-devel@nongnu.org; Fri, 07 Sep 2018 10:51:19 -0400 Received: from mail-wm0-x244.google.com ([2a00:1450:400c:c09::244]:52195) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1fyI6M-0007mN-T5 for qemu-devel@nongnu.org; Fri, 07 Sep 2018 10:51:15 -0400 Received: by mail-wm0-x244.google.com with SMTP id y2-v6so15029355wma.1 for ; Fri, 07 Sep 2018 07:51:14 -0700 (PDT) References: <20180817232923.28899-1-cota@braap.org> <20180817232923.28899-3-cota@braap.org> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <20180817232923.28899-3-cota@braap.org> Date: Fri, 07 Sep 2018 15:51:12 +0100 Message-ID: <87in3hz7hb.fsf@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 2/6] qht: add qht_iter_remove List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Emilio G. Cota" Cc: qemu-devel@nongnu.org, Richard Henderson Emilio G. Cota 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 > --- > 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, voi= d *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 *us= erp); > + > /** > * 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, uint3= 2_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 *he= ad, > + const struct qht_iter *iter, void *us= erp) > { > + struct qht_bucket *b =3D head; > int i; > > do { > @@ -716,7 +730,25 @@ static inline void qht_bucket_iter(struct qht *ht, s= truct qht_bucket *b, > if (b->pointers[i] =3D=3D 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], us= erp)) { > + /* replace i with the last valid element in the buck= et */ > + 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 =3D 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_m= ap *map, > - qht_iter_func_t func, void *= userp) > + const struct qht_iter *iter, > + void *userp) > { > size_t i; > > for (i =3D 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 =3D atomic_rcu_read(&ht->map); > qht_map_lock_buckets(map); > /* Note: ht here is merely for carrying ht->mode; ht->map won't be r= ead */ > - 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 =3D { > + .f.retvoid =3D func, > + .type =3D QHT_ITER_VOID, > + }; > + > + do_qht_iter(ht, &iter, userp); > +} > + > +void qht_iter_remove(struct qht *ht, qht_iter_bool_func_t func, void *us= erp) > +{ > + const struct qht_iter iter =3D { > + .f.retbool =3D func, > + .type =3D QHT_ITER_RM, > + }; > + > + do_qht_iter(ht, &iter, userp); > +} > + > static void qht_map_copy(struct qht *ht, void *p, uint32_t hash, void *u= serp) > { > struct qht_map *new =3D userp; > @@ -760,6 +814,10 @@ static void qht_map_copy(struct qht *ht, void *p, ui= nt32_t hash, void *userp) > static void qht_do_resize_reset(struct qht *ht, struct qht_map *new, boo= l reset) > { > struct qht_map *old; > + const struct qht_iter iter =3D { > + .f.retvoid =3D qht_map_copy, > + .type =3D QHT_ITER_VOID, > + }; > > old =3D ht->map; > qht_map_lock_buckets(old); > @@ -774,7 +832,7 @@ static void qht_do_resize_reset(struct qht *ht, struc= t qht_map *new, bool reset) > } > > g_assert(new->n_buckets !=3D 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 Benn=C3=A9e -- Alex Benn=C3=A9e