Patchwork [1/2] object: introduce Qref to abstract the refcnt interface

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Submitter pingfan liu
Date July 15, 2013, 2:49 a.m.
Message ID <1373856556-22272-1-git-send-email-pingfank@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/258932/
State New
Headers show

Comments

pingfan liu - July 15, 2013, 2:49 a.m.
Qref is similar to kref. It hides the refcnt detail and provides
a common interface. And this patch is based on the idiom of refcnt,
and adopts some optimization about memory model, which finally
falls back on gcc implementation.

Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
---
 include/qom/object.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)
Paolo Bonzini - July 15, 2013, 11:38 a.m.
Il 15/07/2013 04:49, Liu Ping Fan ha scritto:
> Qref is similar to kref. It hides the refcnt detail and provides
> a common interface. And this patch is based on the idiom of refcnt,
> and adopts some optimization about memory model, which finally
> falls back on gcc implementation.
> 
> Signed-off-by: Liu Ping Fan <pingfank@linux.vnet.ibm.com>
> ---
>  include/qom/object.h | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
> 
> diff --git a/include/qom/object.h b/include/qom/object.h
> index 23fc048..2e165fb 100644
> --- a/include/qom/object.h
> +++ b/include/qom/object.h
> @@ -18,6 +18,7 @@
>  #include <stdint.h>
>  #include <stdbool.h>
>  #include "qemu/queue.h"
> +#include "qemu/osdep.h"
>  
>  struct Visitor;
>  struct Error;
> @@ -363,6 +364,10 @@ struct ObjectClass
>      ObjectUnparent *unparent;
>  };
>  
> +typedef struct Qref {
> +    int32_t count;
> +} Qref;
> +
>  /**
>   * Object:
>   *
> @@ -1133,5 +1138,34 @@ int object_child_foreach(Object *obj, int (*fn)(Object *child, void *opaque),
>   */
>  Object *container_get(Object *root, const char *path);
>  
> +static inline void qref_get(Qref *qref)
> +{
> +#ifdef __ATOMIC_RELAXED
> +    __atomic_fetch_add(&qref->count, 1, __ATOMIC_RELAXED);
> +#else
> +    __sync_fetch_and_add(&qref->count, 1);
> +#endif
> +}
> +
> +typedef void (*ReleaseFn)(Qref *);
>  
> +static inline void qref_put(Qref *qref, ReleaseFn release)
> +{
> +    int32_t i;
> +
> +#ifdef __ATOMIC_RELAXED
> +    i = __atomic_fetch_add(&qref->count, -1, __ATOMIC_RELAXED);
> +    g_assert(i > 0);
> +    if (unlikely(i == 1)) {
> +        __atomic_thread_fence(__ATOMIC_SEQ_CST);
> +        release(qref);
> +    }
> +#else
> +    i = __sync_fetch_and_add(&qref->count, -1);
> +    g_assert(i > 0);
> +    if (unlikely(i == 1)) {
> +        release(qref);
> +    }
> +#endif
> +}
>  #endif
> 

I don't think this should depend on QOM, so include/qom/object.h is not
the right place to put it.  I suggested a different way in the other thread.

Also, get/put is not used (except in a couple places for historical
reasons) in QEMU.

Paolo

Patch

diff --git a/include/qom/object.h b/include/qom/object.h
index 23fc048..2e165fb 100644
--- a/include/qom/object.h
+++ b/include/qom/object.h
@@ -18,6 +18,7 @@ 
 #include <stdint.h>
 #include <stdbool.h>
 #include "qemu/queue.h"
+#include "qemu/osdep.h"
 
 struct Visitor;
 struct Error;
@@ -363,6 +364,10 @@  struct ObjectClass
     ObjectUnparent *unparent;
 };
 
+typedef struct Qref {
+    int32_t count;
+} Qref;
+
 /**
  * Object:
  *
@@ -1133,5 +1138,34 @@  int object_child_foreach(Object *obj, int (*fn)(Object *child, void *opaque),
  */
 Object *container_get(Object *root, const char *path);
 
+static inline void qref_get(Qref *qref)
+{
+#ifdef __ATOMIC_RELAXED
+    __atomic_fetch_add(&qref->count, 1, __ATOMIC_RELAXED);
+#else
+    __sync_fetch_and_add(&qref->count, 1);
+#endif
+}
+
+typedef void (*ReleaseFn)(Qref *);
 
+static inline void qref_put(Qref *qref, ReleaseFn release)
+{
+    int32_t i;
+
+#ifdef __ATOMIC_RELAXED
+    i = __atomic_fetch_add(&qref->count, -1, __ATOMIC_RELAXED);
+    g_assert(i > 0);
+    if (unlikely(i == 1)) {
+        __atomic_thread_fence(__ATOMIC_SEQ_CST);
+        release(qref);
+    }
+#else
+    i = __sync_fetch_and_add(&qref->count, -1);
+    g_assert(i > 0);
+    if (unlikely(i == 1)) {
+        release(qref);
+    }
+#endif
+}
 #endif