[vlc-devel] [RFC] [NOT FOR MERGE] objres: add mutex support

[Rémi Denis-Courmont]

This adds a function to allocate a mutex that automatically gets
destroyed when a module fails or terminates.

I have very mixed feelings about this, as it introduces an error return
where there is normally none, i.e., from vlc_mutex_init(). It also
requires tedious rework to replace `vlc_mutex_t' with `vlc_mutex_t *'.

For reference, kernel code entirely solves this conundrum by not
requiring explicit mutex destruction (a kernel mutex does not hold any
resource besides its own `struct mutex' storage space). This could also
be done, but with significant reworking of the VLC threading layer and
prevents reliable detection of attempt to delete a still-in-use mutex.
---
 include/vlc_objects.h |  2 ++
 src/misc/objres.c     | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/include/vlc_objects.h b/include/vlc_objects.h
index 19ee5207fc..32f23abf41 100644
--- a/include/vlc_objects.h
+++ b/include/vlc_objects.h
@@ -295,5 +295,7 @@ VLC_API VLC_MALLOC char *vlc_obj_strdup(vlc_object_t *obj, const char *str);
  */
 VLC_API void vlc_obj_free(vlc_object_t *obj, void *ptr);
 
+VLC_API VLC_MALLOC vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj);
+
 /** @} */
 /** @} */
diff --git a/src/misc/objres.c b/src/misc/objres.c
index cac8624e7e..383dd760a8 100644
--- a/src/misc/objres.c
+++ b/src/misc/objres.c
@@ -174,3 +174,18 @@ void vlc_obj_free(vlc_object_t *obj, void *ptr)
 {
     vlc_objres_remove(obj, ptr, ptrcmp);
 }
+
+static void mutex_release(void *data)
+{
+    vlc_mutex_destroy(data);
+}
+
+vlc_mutex_t *vlc_obj_mutex_new(vlc_object_t *obj)
+{
+    vlc_mutex_t *mtx = vlc_objres_new(sizeof (*mtx), mutex_release);
+    if (mtx != NULL) {
+        vlc_mutex_init(mtx);
+        vlc_objres_push(obj, mtx);
+    }
+    return mtx;
+}
-- 
2.25.0