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Merge branch '931-gprivate-optimisations' into 'main'

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GPrivate: eliminate a malloc for pthread_key_t on most platforms

Closes #931

See merge request GNOME/glib!3507
This commit is contained in:
Emmanuele Bassi 2023-07-30 10:56:53 +00:00
commit 0cc84f9f3e
1 changed files with 90 additions and 13 deletions
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103
glib/gthread-posix.c
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@ -1047,24 +1047,101 @@ g_private_impl_free (pthread_key_t *key)
free (key);
}
static inline pthread_key_t *
g_private_get_impl (GPrivate *key)
static gpointer
g_private_impl_new_direct (GDestroyNotify notify)
{
pthread_key_t *impl = g_atomic_pointer_get (&key->p);
gpointer impl = (void *) (gssize) -1;
pthread_key_t key;
gint status;
if G_UNLIKELY (impl == NULL)
status = pthread_key_create (&key, notify);
if G_UNLIKELY (status != 0)
g_thread_abort (status, "pthread_key_create");
memcpy (&impl, &key, sizeof (pthread_key_t));
/* pthread_key_create could theoretically put a NULL value into key.
* If that happens, waste the result and create a new one, since we
* use NULL to mean "not yet allocated".
*
* This will only happen once per program run.
*
* We completely avoid this problem for the case where pthread_key_t
* is smaller than void* (for example, on 64 bit Linux) by putting
* some high bits in the value of 'impl' to start with. Since we only
* overwrite part of the pointer, we will never end up with NULL.
*/
if (sizeof (pthread_key_t) == sizeof (gpointer))
{
impl = g_private_impl_new (key->notify);
if (!g_atomic_pointer_compare_and_exchange (&key->p, NULL, impl))
if G_UNLIKELY (impl == NULL)
{
g_private_impl_free (impl);
impl = key->p;
status = pthread_key_create (&key, notify);
if G_UNLIKELY (status != 0)
g_thread_abort (status, "pthread_key_create");
memcpy (&impl, &key, sizeof (pthread_key_t));
if G_UNLIKELY (impl == NULL)
g_thread_abort (status, "pthread_key_create (gave NULL result twice)");
}
}
return impl;
}
static void
g_private_impl_free_direct (gpointer impl)
{
pthread_key_t tmp;
gint status;
memcpy (&tmp, &impl, sizeof (pthread_key_t));
status = pthread_key_delete (tmp);
if G_UNLIKELY (status != 0)
g_thread_abort (status, "pthread_key_delete");
}
static inline pthread_key_t
g_private_get_impl (GPrivate *key)
{
if (sizeof (pthread_key_t) > sizeof (gpointer))
{
pthread_key_t *impl = g_atomic_pointer_get (&key->p);
if G_UNLIKELY (impl == NULL)
{
impl = g_private_impl_new (key->notify);
if (!g_atomic_pointer_compare_and_exchange (&key->p, NULL, impl))
{
g_private_impl_free (impl);
impl = key->p;
}
}
return *impl;
}
else
{
gpointer impl = g_atomic_pointer_get (&key->p);
pthread_key_t tmp;
if G_UNLIKELY (impl == NULL)
{
impl = g_private_impl_new_direct (key->notify);
if (!g_atomic_pointer_compare_and_exchange (&key->p, NULL, impl))
{
g_private_impl_free_direct (impl);
impl = key->p;
}
}
memcpy (&tmp, &impl, sizeof (pthread_key_t));
return tmp;
}
}
/**
* g_private_get:
* @key: a #GPrivate
@ -1081,7 +1158,7 @@ gpointer
g_private_get (GPrivate *key)
{
/* quote POSIX: No errors are returned from pthread_getspecific(). */
return pthread_getspecific (*g_private_get_impl (key));
return pthread_getspecific (g_private_get_impl (key));
}
/**
@ -1101,7 +1178,7 @@ g_private_set (GPrivate *key,
{
gint status;
if G_UNLIKELY ((status = pthread_setspecific (*g_private_get_impl (key), value)) != 0)
if G_UNLIKELY ((status = pthread_setspecific (g_private_get_impl (key), value)) != 0)
g_thread_abort (status, "pthread_setspecific");
}
@ -1123,13 +1200,13 @@ void
g_private_replace (GPrivate *key,
gpointer value)
{
pthread_key_t *impl = g_private_get_impl (key);
pthread_key_t impl = g_private_get_impl (key);
gpointer old;
gint status;
old = pthread_getspecific (*impl);
old = pthread_getspecific (impl);
if G_UNLIKELY ((status = pthread_setspecific (*impl, value)) != 0)
if G_UNLIKELY ((status = pthread_setspecific (impl, value)) != 0)
g_thread_abort (status, "pthread_setspecific");
if (old && key->notify)