[vlc-devel] [PATCH] libvlc: dump object types abd names when leaking

[Rémi Denis-Courmont]

Hi,

Well I did debug that assertion failure using (ASan +) gdb just fine last time. The code has not changed. So this kludge is definitely not necessary for its alleged purpose.

Not only that but stderr is not universally the output for debug nor is it universally where assertion failures are dumped to, so this patch does not even work properly

And in most cases you can see the leak by stopping all inputs and dumping the objects tree before quitting, anyway.

Le 21 février 2019 11:24:57 GMT+02:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>Comment:
>A lot of developers asked me to propose this patch again. It was
>previously
>refused because developers could use proper debugging tools. I disagree
>with
>that assumption. Even with Asan, when the leak assert fail, it will
>abort()
>without prompting any leaks, so you'll have to edit libvlc.c to remove
>this
>assert. If your leak was not reproducible, you'll lose a precious
>information.
>And good luck finding the leak with GDB, you really need to know the
>internal
>of vlc_object_t to iterate through the different list to get the
>culprit.
>
>Commit log:
>
>In case of a vlc_object_t leak, and if asserts are enabled, the error
>output
>will be like the following (when leaking intentionally decoder_t
>objects):
>
>=== vlc_object LEAKS detected ===
>  \ playlist
>  |   \ input
>  |   |   \ decoder avcodec
>  |   |   | decoder faad
>  |   |   | decoder stl
>---
> src/libvlc.c | 30 ++++++++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
>
>diff --git a/src/libvlc.c b/src/libvlc.c
>index 8e8d2ca8b2..d9ff96de84 100644
>--- a/src/libvlc.c
>+++ b/src/libvlc.c
>@@ -436,6 +436,24 @@ void libvlc_InternalCleanup( libvlc_int_t
>*p_libvlc )
> #endif
> }
> 
>+#ifndef NDEBUG
>+static void DumpObjectLeaks(vlc_object_internals_t *priv, unsigned
>level)
>+{
>+    bool first = true;
>+    vlc_list_foreach(priv, &priv->children, siblings)
>+    {
>+        vlc_object_t *obj = vlc_externals(priv);
>+        for (unsigned i = 0; i < level; i++)
>+            fprintf(stderr, "  %s ", first && i == level -1 ? "\\" :
>"|");
>+        char *name = vlc_object_get_name(obj);
>+        fprintf(stderr, "%s %s\n", vlc_object_typename(obj), name ?
>name : "");
>+        free(name);
>+        DumpObjectLeaks(priv, level + 1);
>+        first = false;
>+    }
>+}
>+#endif
>+
> /**
>  * Destroy everything.
>* This function requests the running threads to finish, waits for their
>@@ -449,6 +467,18 @@ void libvlc_InternalDestroy( libvlc_int_t
>*p_libvlc )
> 
>     vlc_ExitDestroy( &priv->exit );
> 
>+#ifndef NDEBUG
>+    {
>+        vlc_object_internals_t *internal = vlc_internals(p_libvlc);
>+        if (atomic_load(&internal->refs) != 1)
>+        {
>+            vlc_mutex_lock(&internal->tree_lock);
>+            fprintf(stderr, "=== vlc_object LEAKS detected ===\n");
>+            DumpObjectLeaks(internal, 1);
>+            vlc_mutex_unlock(&internal->tree_lock);
>+        }
>+    }
>+#endif
>     assert( atomic_load(&(vlc_internals(p_libvlc)->refs)) == 1 );
>     vlc_object_release( p_libvlc );
> }
>-- 
>2.20.1
>
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