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gvarianttype: Garbage Collect GVariantTypeInfo

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The goal of this change is to avoid re-parsing `GVariantTypeInfo` on
every creation or parsing of a `GVariant` byte-buffer. Parsing presents
a non-trivial amount of overhead which can typically be elided.

It was discovered that many applications and tooling are re-generating
this information upon receiving a D-Bus message as they tend to process
messages serially, thus dropping the last reference count.

Previously, when the last reference count for a `GVariantTypeInfo` was
dropped we would finalize the parsed type information.

This change keeps `GVariantTypeInfo` alive in a Garbage Collected array.
The array is collected upon reaching a 32 entries. The number 32 was
chosen because it is larger than what I've seen active on various D-Bus
based applications-or-daemons.

Take a simple test case of using `GVariantBuilder` in a loop with a
debugoptimized build of GLib. A reduction in wallclock time can be
observed in the 35% to more than 70% based on the complexity of the
GVariant being created.

For cases like ibus-daemon, it was previously parsing `GVariantTypeInfo`
up to dozens of times per key-press/release cycle.

Closes: #3472
This commit is contained in:
Christian Hergert 2024-09-14 02:35:17 -07:00 committed by Philip Withnall
parent 26d8553af5
commit 67532b4555
1 changed files with 50 additions and 23 deletions
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73
glib/gvarianttypeinfo.c
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@ -740,6 +740,36 @@ g_variant_type_info_member_info (GVariantTypeInfo *info,
/* == new/ref/unref == */
static GRecMutex g_variant_type_info_lock;
static GHashTable *g_variant_type_info_table;
static GPtrArray *g_variant_type_info_gc;
#define GC_THRESHOLD 32
static void
gc_while_locked (void)
{
while (g_variant_type_info_gc->len > 0)
{
GVariantTypeInfo *info = g_ptr_array_steal_index_fast (g_variant_type_info_gc, 0);
ContainerInfo *container = (ContainerInfo *)info;
if (g_atomic_ref_count_dec (&container->ref_count))
{
TRACE(GLIB_VARIANT_TYPE_INFO_FREE(info));
g_hash_table_remove (g_variant_type_info_table,
container->type_string);
g_free (container->type_string);
if (info->container_class == GV_ARRAY_INFO_CLASS)
array_info_free (info);
else if (info->container_class == GV_TUPLE_INFO_CLASS)
tuple_info_free (info);
else
g_assert_not_reached ();
}
}
}
/* < private >
* g_variant_type_info_get:
@ -864,36 +894,33 @@ g_variant_type_info_unref (GVariantTypeInfo *info)
g_rec_mutex_lock (&g_variant_type_info_lock);
if (g_atomic_ref_count_dec (&container->ref_count))
{
if (g_variant_type_info_gc == NULL)
g_variant_type_info_gc = g_ptr_array_new ();
TRACE(GLIB_VARIANT_TYPE_INFO_FREE(info));
/* Steal this instance and place it onto the GC queue.
* We may bring it back to life before the next GC.
*/
g_atomic_ref_count_init (&container->ref_count);
g_ptr_array_add (g_variant_type_info_gc, info);
g_hash_table_remove (g_variant_type_info_table,
container->type_string);
if (g_hash_table_size (g_variant_type_info_table) == 0)
{
g_hash_table_unref (g_variant_type_info_table);
g_variant_type_info_table = NULL;
}
g_rec_mutex_unlock (&g_variant_type_info_lock);
g_free (container->type_string);
if (info->container_class == GV_ARRAY_INFO_CLASS)
array_info_free (info);
else if (info->container_class == GV_TUPLE_INFO_CLASS)
tuple_info_free (info);
else
g_assert_not_reached ();
if (g_variant_type_info_gc->len > GC_THRESHOLD)
gc_while_locked ();
}
else
g_rec_mutex_unlock (&g_variant_type_info_lock);
g_rec_mutex_unlock (&g_variant_type_info_lock);
}
}
void
g_variant_type_info_assert_no_infos (void)
{
g_assert (g_variant_type_info_table == NULL);
G_GNUC_UNUSED gboolean empty;
g_rec_mutex_lock (&g_variant_type_info_lock);
if (g_variant_type_info_table != NULL)
gc_while_locked ();
empty = (g_variant_type_info_table == NULL ||
g_hash_table_size (g_variant_type_info_table) == 0);
g_rec_mutex_unlock (&g_variant_type_info_lock);
g_assert (empty);
}