win32: add COM-specific SAFE_RELEASE to windows_utils.h

See: https://msdn.microsoft.com/en-us/library/windows/desktop/dd743946.aspx

Microsoft example code often uses a SAFE_RELEASE macro like the one in
the above link. This makes it easier to avoid errors when releasing COM
interfaces. It also reduces noise in COM-heavy code.

ao_wasapi.h also had a macro called SAFE_RELEASE, though unlike the
version above, its SAFE_RELEASE macro accepted a second parameter which
allowed it to destroy arbitrary objects other than just COM interfaces.
This renames ao_wasapi's SAFE_RELEASE to SAFE_DESTROY, which should more
accurately reflect what it does and prevent confusion with the Microsoft
version.

1 files changed, 4 insertions, 0 deletions

diff --git a/osdep/windows_utils.h b/osdep/windows_utils.h
index 6c750ded2a..a20a558709 100644
--- a/osdep/windows_utils.h
+++ b/osdep/windows_utils.h
@@ -20,6 +20,10 @@
 
 #include <windows.h>
 
+// Conditionally release a COM interface and set the pointer to NULL
+#define SAFE_RELEASE(u) \
+    do { if ((u) != NULL) (u)->lpVtbl->Release(u); (u) = NULL; } while(0)
+
 char *mp_GUID_to_str_buf(char *buf, size_t buf_size, const GUID *guid);
 #define mp_GUID_to_str(guid) mp_GUID_to_str_buf((char[40]){0}, 40, (guid))
 char *mp_HRESULT_to_str_buf(char *buf, size_t buf_size, HRESULT hr);