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gtimezone: Cache default timezone indefinitely

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We cache GTimeZone instances to avoid expensive construction when the
same id is requested again.

However, if the NULL id is passed to g_time_zone_new(), we always
construct a new instance for the default/fallback timezone.

With the recent introduction of some heavy calculations[1], repeated
instance construction in such cases has visible performance impact in
nautilus list view and other such GtkTreeView consumers.

To avoid this, cache reference to a constructed default timezone and
use it the next time g_time_zone_new() is called with NULL argument,
as long as the default identifier doesn't change. We already did the
same for the local timezone[2].

Fixes: https://gitlab.gnome.org/GNOME/glib/-/issues/2204

Based on idea proposed by Sebastian Keller <skeller@gnome.org>.

[1] 25d950b61f
[2] 551e83662d
This commit is contained in:
António Fernandes 2020-10-01 21:11:44 +01:00 committed by Philip Withnall
parent 19c5e13fc4
commit 3ab278dab0
1 changed files with 39 additions and 6 deletions
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37
glib/gtimezone.c
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@ -195,6 +195,8 @@ struct _GTimeZone
G_LOCK_DEFINE_STATIC (time_zones);
static GHashTable/*<string?, GTimeZone>*/ *time_zones;
G_LOCK_DEFINE_STATIC (tz_default);
static GTimeZone *tz_default = NULL;
G_LOCK_DEFINE_STATIC (tz_local);
static gchar *tzenv_cached = NULL;
static GTimeZone *tz_local = NULL;
@ -239,6 +241,7 @@ again:
goto again;
}
if (time_zones != NULL)
g_hash_table_remove (time_zones, tz->name);
G_UNLOCK(time_zones);
}
@ -1675,12 +1678,12 @@ g_time_zone_new (const gchar *identifier)
gint rules_num;
gchar *resolved_identifier = NULL;
if (identifier)
{
G_LOCK (time_zones);
if (time_zones == NULL)
time_zones = g_hash_table_new (g_str_hash, g_str_equal);
if (identifier)
{
tz = g_hash_table_lookup (time_zones, identifier);
if (tz)
{
@ -1693,11 +1696,31 @@ g_time_zone_new (const gchar *identifier)
}
else
{
G_LOCK (tz_default);
#ifdef G_OS_UNIX
resolved_identifier = zone_identifier_unix ();
#elif defined (G_OS_WIN32)
resolved_identifier = windows_default_tzname ();
#endif
if (tz_default)
{
/* Flush default if changed. If the identifier couldn’t be resolved,
* we’re going to fall back to UTC eventually, so don’t clear out the
* cache if it’s already UTC. */
if (!(resolved_identifier == NULL && g_str_equal (tz_default->name, "UTC")) &&
g_strcmp0 (tz_default->name, resolved_identifier) != 0)
{
g_clear_pointer (&tz_default, g_time_zone_unref);
}
else
{
tz = g_time_zone_ref (tz_default);
G_UNLOCK (tz_default);
g_free (resolved_identifier);
return tz;
}
}
}
tz = g_slice_new0 (GTimeZone);
@ -1773,9 +1796,19 @@ g_time_zone_new (const gchar *identifier)
{
if (identifier)
g_hash_table_insert (time_zones, tz->name, tz);
else if (tz->name)
{
/* Caching reference */
g_atomic_int_inc (&tz->ref_count);
tz_default = tz;
}
}
g_atomic_int_inc (&tz->ref_count);
if (identifier)
G_UNLOCK (time_zones);
else
G_UNLOCK (tz_default);
return tz;
}