d3d: simplify DLL loading

For some reason, the d3d9/dxva2/d3d11 DLLs are still optional. But we
don't need to try so hard to keep exact references. In fact, there's no
reason to unload them at all.

So load them once in a central place. For simplicity, the d3d9/d3d11
backends both load all DLLs. (They will error out only if the required
DLLs could not be loaded.)

In theory, we could just call LoadLibrary multiple times (without
calling FreeLibrary), but I'm slightly worried that this could be
detected as a "bug", or that the reference count could even have a low
static limit that could be hit soon.

4 files changed, 34 insertions, 49 deletions

diff --git a/video/decode/d3d.c b/video/decode/d3d.c
index df10c9fe19..b978472723 100644
--- a/video/decode/d3d.c
+++ b/video/decode/d3d.c
@@ -15,6 +15,8 @@
  * License along with mpv.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <pthread.h>
+
 #include <libavcodec/avcodec.h>
 
 #include "lavc.h"
@@ -96,6 +98,22 @@ static const struct d3dva_mode d3dva_modes[] = {
 #undef MODE
 #undef MODE2
 
+HMODULE d3d11_dll, d3d9_dll, dxva2_dll;
+
+static pthread_once_t d3d_load_once = PTHREAD_ONCE_INIT;
+
+static void d3d_do_load(void)
+{
+    d3d11_dll = LoadLibrary(L"d3d11.dll");
+    d3d9_dll  = LoadLibrary(L"d3d9.dll");
+    dxva2_dll = LoadLibrary(L"dxva2.dll");
+}
+
+void d3d_load_dlls(void)
+{
+    pthread_once(&d3d_load_once, d3d_do_load);
+}
+
 int d3d_probe_codec(const char *codec)
 {
     enum AVCodecID codecid = mp_codec_to_av_codec_id(codec);
diff --git a/video/decode/d3d.h b/video/decode/d3d.h
index 3f5b8aebe7..15c423ab8c 100644
--- a/video/decode/d3d.h
+++ b/video/decode/d3d.h
@@ -36,6 +36,12 @@ struct d3d_decoder_fmt {
     const struct d3d_decoded_format *format;
 };
 
+// Must call d3d_load_dlls() before accessing. Once this is done, the DLLs
+// remain loaded forever.
+extern HMODULE d3d11_dll, d3d9_dll, dxva2_dll;
+
+void d3d_load_dlls(void);
+
 int d3d_probe_codec(const char *codec);
 
 struct d3d_decoder_fmt d3d_select_decoder_mode(
diff --git a/video/decode/d3d11va.c b/video/decode/d3d11va.c
index d631fff479..dd4535bdd7 100644
--- a/video/decode/d3d11va.c
+++ b/video/decode/d3d11va.c
@@ -40,7 +40,6 @@ struct d3d11va_decoder {
 struct priv {
     struct mp_log *log;
 
-    HMODULE                 d3d11_dll;
     ID3D11Device           *device;
     ID3D11DeviceContext    *device_ctx;
     ID3D11VideoDevice      *video_dev;
@@ -51,7 +50,6 @@ struct priv {
 };
 
 struct d3d11va_surface {
-    HMODULE d3d11_dll;
     ID3D11Texture2D              *texture;
     int                          subindex;
     ID3D11VideoDecoderOutputView *surface;
@@ -66,9 +64,6 @@ static void d3d11va_release_img(void *arg)
     if (surface->texture)
         ID3D11Texture2D_Release(surface->texture);
 
-    if (surface->d3d11_dll)
-        FreeLibrary(surface->d3d11_dll);
-
     talloc_free(surface);
 }
 
@@ -79,10 +74,6 @@ static struct mp_image *d3d11va_new_ref(ID3D11VideoDecoderOutputView *view,
         return NULL;
     struct d3d11va_surface *surface = talloc_zero(NULL, struct d3d11va_surface);
 
-    surface->d3d11_dll = LoadLibrary(L"d3d11.dll");
-    if (!surface->d3d11_dll)
-        goto fail;
-
     surface->surface = view;
     ID3D11VideoDecoderOutputView_AddRef(surface->surface);
     ID3D11VideoDecoderOutputView_GetResource(
@@ -105,9 +96,6 @@ static struct mp_image *d3d11va_new_ref(ID3D11VideoDecoderOutputView *view,
     mpi->planes[3] = (void *)surface->surface;
 
     return mpi;
-fail:
-    d3d11va_release_img(surface);
-    return NULL;
 }
 
 static struct mp_image *d3d11va_allocate_image(struct lavc_ctx *s, int w, int h)
@@ -434,9 +422,6 @@ static void destroy_device(struct lavc_ctx *s)
 
     if (p->device_ctx)
         ID3D11DeviceContext_Release(p->device_ctx);
-
-    if (p->d3d11_dll)
-        FreeLibrary(p->d3d11_dll);
 }
 
 static bool create_device(struct lavc_ctx *s, BOOL thread_safe)
@@ -444,14 +429,14 @@ static bool create_device(struct lavc_ctx *s, BOOL thread_safe)
     HRESULT hr;
     struct priv *p = s->hwdec_priv;
 
-    p->d3d11_dll = LoadLibrary(L"d3d11.dll");
-    if (!p->d3d11_dll) {
+    d3d_load_dlls();
+    if (!d3d11_dll) {
         MP_ERR(p, "Failed to load D3D11 library\n");
         return false;
     }
 
     PFN_D3D11_CREATE_DEVICE CreateDevice =
-        (void *)GetProcAddress(p->d3d11_dll, "D3D11CreateDevice");
+        (void *)GetProcAddress(d3d11_dll, "D3D11CreateDevice");
     if (!CreateDevice) {
         MP_ERR(p, "Failed to get D3D11CreateDevice symbol from DLL: %s\n",
                mp_LastError_to_str());
diff --git a/video/decode/dxva2.c b/video/decode/dxva2.c
index 829d77ccbf..489f580fc0 100644
--- a/video/decode/dxva2.c
+++ b/video/decode/dxva2.c
@@ -39,8 +39,6 @@
 struct priv {
     struct mp_log *log;
 
-    HMODULE                      d3d9_dll;
-    HMODULE                      dxva2_dll;
     IDirect3D9                  *d3d9;
     IDirect3DDevice9            *device;
     HANDLE                       device_handle;
@@ -53,9 +51,6 @@ struct priv {
 };
 
 struct dxva2_surface {
-    HMODULE d3dlib;
-    HMODULE dxva2lib;
-
     IDirectXVideoDecoder *decoder;
     IDirect3DSurface9    *surface;
 };
@@ -69,12 +64,6 @@ static void dxva2_release_img(void *arg)
     if (surface->decoder)
         IDirectXVideoDecoder_Release(surface->decoder);
 
-    if (surface->dxva2lib)
-        FreeLibrary(surface->dxva2lib);
-
-    if (surface->d3dlib)
-        FreeLibrary(surface->d3dlib);
-
     talloc_free(surface);
 }
 
@@ -86,13 +75,6 @@ static struct mp_image *dxva2_new_ref(IDirectXVideoDecoder *decoder,
         return NULL;
     struct dxva2_surface *surface = talloc_zero(NULL, struct dxva2_surface);
 
-    // Add additional references to the libraries which might otherwise be freed
-    // before the surface, which is observed to lead to bad behaviour
-    surface->d3dlib   = LoadLibrary(L"d3d9.dll");
-    surface->dxva2lib = LoadLibrary(L"dxva2.dll");
-    if (!surface->d3dlib || !surface->dxva2lib)
-        goto fail;
-
     surface->surface = d3d9_surface;
     IDirect3DSurface9_AddRef(surface->surface);
     surface->decoder = decoder;
@@ -368,25 +350,20 @@ static void destroy_device(struct lavc_ctx *s)
 
     if (p->d3d9)
         IDirect3D9_Release(p->d3d9);
-
-    if (p->d3d9_dll)
-        FreeLibrary(p->d3d9_dll);
-
-    if (p->dxva2_dll)
-        FreeLibrary(p->dxva2_dll);
 }
 
 static bool create_device(struct lavc_ctx *s)
 {
     struct priv *p = s->hwdec_priv;
-    p->d3d9_dll = LoadLibrary(L"d3d9.dll");
-    if (!p->d3d9_dll) {
+
+    d3d_load_dlls();
+    if (!d3d9_dll) {
         MP_ERR(p, "Failed to load D3D9 library\n");
         return false;
     }
 
     IDirect3D9* (WINAPI *Direct3DCreate9)(UINT) =
-        (void *)GetProcAddress(p->d3d9_dll, "Direct3DCreate9");
+        (void *)GetProcAddress(d3d9_dll, "Direct3DCreate9");
     if (!Direct3DCreate9) {
         MP_ERR(p, "Failed to locate Direct3DCreate9\n");
         return false;
@@ -477,15 +454,14 @@ static int dxva2_init(struct lavc_ctx *s)
             goto fail;
     }
 
-    p->dxva2_dll = LoadLibrary(L"dxva2.dll");
-    if (!p->dxva2_dll) {
+    d3d_load_dlls();
+    if (!dxva2_dll) {
         MP_ERR(p, "Failed to load DXVA2 library\n");
         goto fail;
     }
 
     HRESULT (WINAPI *CreateDeviceManager9)(UINT *, IDirect3DDeviceManager9 **) =
-        (void *)GetProcAddress(p->dxva2_dll,
-                               "DXVA2CreateDirect3DDeviceManager9");
+        (void *)GetProcAddress(dxva2_dll, "DXVA2CreateDirect3DDeviceManager9");
     if (!CreateDeviceManager9) {
         MP_ERR(p, "Failed to locate DXVA2CreateDirect3DDeviceManager9\n");
         goto fail;