[vlc-commits] objects: use atomic reference counter instead of spin lock + counter
Rémi Denis-Courmont
git at videolan.org
Sat Nov 10 18:01:15 CET 2012
vlc | branch: master | Rémi Denis-Courmont <remi at remlab.net> | Sat Nov 10 18:59:18 2012 +0200| [95b0fabc32bdc5886aa32c40bec421c99320107c] | committer: Rémi Denis-Courmont
objects: use atomic reference counter instead of spin lock + counter
> http://git.videolan.org/gitweb.cgi/vlc.git/?a=commit;h=95b0fabc32bdc5886aa32c40bec421c99320107c
---
src/libvlc.c | 8 +------
src/misc/objects.c | 65 +++++++++++++++++++-------------------------------
src/misc/variables.h | 5 ++--
3 files changed, 28 insertions(+), 50 deletions(-)
diff --git a/src/libvlc.c b/src/libvlc.c
index abbe7d3..65e27fe 100644
--- a/src/libvlc.c
+++ b/src/libvlc.c
@@ -682,13 +682,7 @@ void libvlc_InternalDestroy( libvlc_int_t *p_libvlc )
vlc_ExitDestroy( &priv->exit );
vlc_mutex_destroy( &priv->ml_lock );
-#ifndef NDEBUG /* Hack to dump leaked objects tree */
- if( vlc_internals( p_libvlc )->i_refcount > 1 )
- while( vlc_internals( p_libvlc )->i_refcount > 0 )
- vlc_object_release( p_libvlc );
-#endif
-
- assert( vlc_internals( p_libvlc )->i_refcount == 1 );
+ assert( atomic_load(&(vlc_internals(p_libvlc)->refs)) == 1 );
vlc_object_release( p_libvlc );
}
diff --git a/src/misc/objects.c b/src/misc/objects.c
index c8d90d8..292bba3 100644
--- a/src/misc/objects.c
+++ b/src/misc/objects.c
@@ -133,8 +133,7 @@ void *vlc_custom_create (vlc_object_t *parent, size_t length,
vlc_mutex_init (&priv->var_lock);
vlc_cond_init (&priv->var_wait);
priv->pipes[0] = priv->pipes[1] = -1;
- vlc_spin_init (&priv->ref_spin);
- priv->i_refcount = 1;
+ atomic_init (&priv->refs, 1);
priv->pf_destructor = NULL;
priv->prev = NULL;
priv->first = NULL;
@@ -213,9 +212,7 @@ void vlc_object_set_destructor( vlc_object_t *p_this,
{
vlc_object_internals_t *p_priv = vlc_internals(p_this );
- vlc_spin_lock( &p_priv->ref_spin );
p_priv->pf_destructor = pf_destructor;
- vlc_spin_unlock( &p_priv->ref_spin );
}
static vlc_mutex_t name_lock = VLC_STATIC_MUTEX;
@@ -279,7 +276,6 @@ static void vlc_object_destroy( vlc_object_t *p_this )
free( p_priv->psz_name );
- vlc_spin_destroy( &p_priv->ref_spin );
if( p_priv->pipes[1] != -1 && p_priv->pipes[1] != p_priv->pipes[0] )
close( p_priv->pipes[1] );
if( p_priv->pipes[0] != -1 )
@@ -452,13 +448,9 @@ vlc_object_t *vlc_object_find_name( vlc_object_t *p_this, const char *psz_name )
void * vlc_object_hold( vlc_object_t *p_this )
{
vlc_object_internals_t *internals = vlc_internals( p_this );
+ unsigned refs = atomic_fetch_add (&internals->refs, 1);
- vlc_spin_lock( &internals->ref_spin );
- /* Avoid obvious freed object uses */
- assert( internals->i_refcount > 0 );
- /* Increment the counter */
- internals->i_refcount++;
- vlc_spin_unlock( &internals->ref_spin );
+ assert (refs > 0); /* Avoid obvious freed object uses */ (void) refs;
return p_this;
}
@@ -471,43 +463,38 @@ void vlc_object_release( vlc_object_t *p_this )
{
vlc_object_internals_t *internals = vlc_internals( p_this );
vlc_object_t *parent = NULL;
- bool b_should_destroy;
+ unsigned refs = atomic_load (&internals->refs);
- vlc_spin_lock( &internals->ref_spin );
- assert( internals->i_refcount > 0 );
-
- if( internals->i_refcount > 1 )
+ /* Fast path */
+ while (refs > 1)
{
- /* Fast path */
- /* There are still other references to the object */
- internals->i_refcount--;
- vlc_spin_unlock( &internals->ref_spin );
- return;
+ if (atomic_compare_exchange_weak (&internals->refs, &refs, refs - 1))
+ return; /* There are still other references to the object */
+
+ assert (refs > 0);
}
- vlc_spin_unlock( &internals->ref_spin );
/* Slow path */
- /* Remember that we cannot hold the spin while waiting on the mutex */
libvlc_lock (p_this->p_libvlc);
- /* Take the spin again. Note that another thread may have held the
- * object in the (very short) mean time. */
- vlc_spin_lock( &internals->ref_spin );
- b_should_destroy = --internals->i_refcount == 0;
- vlc_spin_unlock( &internals->ref_spin );
+ refs = atomic_fetch_sub (&internals->refs, 1);
+ assert (refs > 0);
- if( b_should_destroy )
+ if (likely(refs == 1))
{
/* Detach from parent to protect against vlc_object_find_name() */
parent = p_this->p_parent;
if (likely(parent))
{
/* Unlink */
- if (internals->prev != NULL)
- internals->prev->next = internals->next;
+ vlc_object_internals_t *prev = internals->prev;
+ vlc_object_internals_t *next = internals->next;
+
+ if (prev != NULL)
+ prev->next = next;
else
- vlc_internals(parent)->first = internals->next;
- if (internals->next != NULL)
- internals->next->prev = internals->prev;
+ vlc_internals (parent)->first = next;
+ if (next != NULL)
+ next->prev = prev;
}
/* We have no children */
@@ -515,11 +502,9 @@ void vlc_object_release( vlc_object_t *p_this )
}
libvlc_unlock (p_this->p_libvlc);
- if( b_should_destroy )
+ if (likely(refs == 1))
{
- int canc;
-
- canc = vlc_savecancel ();
+ int canc = vlc_savecancel ();
vlc_object_destroy( p_this );
vlc_restorecancel (canc);
if (parent)
@@ -727,9 +712,7 @@ static void PrintObject( vlc_object_internals_t *priv,
}
vlc_mutex_unlock (&name_lock);
- psz_refcount[0] = '\0';
- if( priv->i_refcount > 0 )
- snprintf( psz_refcount, 19, ", %u refs", priv->i_refcount );
+ snprintf( psz_refcount, 19, ", %u refs", atomic_load( &priv->refs ) );
psz_parent[0] = '\0';
/* FIXME: need structure lock!!! */
diff --git a/src/misc/variables.h b/src/misc/variables.h
index 7d56caf..671f337 100644
--- a/src/misc/variables.h
+++ b/src/misc/variables.h
@@ -23,6 +23,8 @@
#ifndef LIBVLC_VARIABLES_H
# define LIBVLC_VARIABLES_H 1
+# include <vlc_atomic.h>
+
/**
* Private LibVLC data for each object.
*/
@@ -41,8 +43,7 @@ struct vlc_object_internals
int pipes[2];
/* Objects management */
- vlc_spinlock_t ref_spin;
- unsigned i_refcount;
+ atomic_uint refs;
vlc_destructor_t pf_destructor;
/* Objects tree structure */
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