ges, gst-python: Fix libpython dlopen on macOS

First encountered at https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1171#note_2290789

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6159>

subprojects/gst-editing-services/ges/ges-formatter.c

@@ -43,7 +43,34 @@
 #ifdef HAS_PYTHON
 #include <Python.h>
 #include "ges-resources.h"
+
+/*
+ * We need to call dlopen() directly on macOS to workaround a macOS runtime
+ * linker bug. When there are nested dlopen() calls and the second dlopen() is
+ * called from another library (such as gmodule), @loader_path is resolved as
+ * @executable_path and RPATHs are read from the executable (gst-plugin-scanner)
+ * instead of the library itself (libgstges.dylib). This doesn't happen if the
+ * second dlopen() call is directly in the source code of the library.
+ * Previously seen at:
+ * https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1171#note_2290789
+ */
+#ifdef G_OS_WIN32
+#include <gmodule.h>
+#define ges_module_open(fname) g_module_open(fname,0)
+#define ges_module_error g_module_error
+#define ges_module_symbol(module,name,symbol) g_module_symbol(module,name,symbol)
+#else
+#include <dlfcn.h>
+#define ges_module_open(fname) dlopen(fname,RTLD_NOW | RTLD_GLOBAL)
+#define ges_module_error dlerror
+static inline gboolean
+ges_module_symbol (gpointer handle, const char *name, gpointer * symbol)
+{
+  *symbol = dlsym (handle, name);
+  return *symbol != NULL;
+}
 #endif
+#endif /* HAS_PYTHON */
 
 GST_DEBUG_CATEGORY_STATIC (ges_formatter_debug);
 #undef GST_CAT_DEFAULT
@@ -558,25 +585,22 @@ load_python_formatters (void)
       G_RESOURCE_LOOKUP_FLAGS_NONE, &err);
   PyObject *code = NULL, *res = NULL;
   gboolean we_initialized = FALSE;
-  GModule *libpython;
   gpointer has_python = NULL;
 
   GST_LOG ("Checking to see if libpython is already loaded");
-  if (g_module_symbol (g_module_open (NULL, G_MODULE_BIND_LOCAL),
+  if (ges_module_symbol (ges_module_open (NULL),
           "_Py_NoneStruct", &has_python) && has_python) {
     GST_LOG ("libpython is already loaded");
   } else {
     GST_LOG ("loading libpython by name: %s", PY_LIB_FNAME);
-    libpython = g_module_open (PY_LIB_FNAME, 0);
-    if (!libpython) {
-      GST_ERROR ("Couldn't g_module_open libpython. Reason: %s",
-          g_module_error ());
+    if (!ges_module_open (PY_LIB_FNAME)) {
+      GST_ERROR ("Couldn't load libpython. Reason: %s", ges_module_error ());
       return;
     }
   }
 
   if (!Py_IsInitialized ()) {
-    GST_LOG ("python wasn't initialized");
+    GST_LOG ("python wasn't already initialized");
     /* set the correct plugin for registering stuff */
     Py_Initialize ();
     we_initialized = TRUE;

subprojects/gst-editing-services/meson.build

@@ -114,6 +114,7 @@ gstvalidate_dep = dependency('gstreamer-validate-1.0', version : gst_req, requir
 
 gio_dep = dependency('gio-2.0', version: glib_req)
 gmodule_dep = dependency('gmodule-no-export-2.0')
+libdl = cc.find_library('dl', required: false)
 libxml_dep = dependency('libxml-2.0', required: get_option('xptv'))
 cdata.set('DISABLE_XPTV', not libxml_dep.found())
 
@@ -202,7 +203,7 @@ elif build_gir and python.found()
     foreach loc: pylib_locs
       foreach fname: pylib_fnames
         if fsmod.exists(loc / fname)
-          libges_deps = libges_deps + [python_dep, gmodule_dep]
+          libges_deps = libges_deps + [python_dep, gmodule_dep, libdl]
           has_python = true
           cdata.set('HAS_PYTHON', true)
           cdata.set_quoted('PY_LIB_FNAME', fname)

subprojects/gst-python/meson.build

@@ -22,6 +22,7 @@ gst_dep = dependency('gstreamer-1.0', version : gst_req,
 gstbase_dep = dependency('gstreamer-base-1.0', version : gst_req,
   fallback : ['gstreamer', 'gst_base_dep'])
 gmodule_dep = dependency('gmodule-no-export-2.0')
+libdl = cc.find_library('dl', required: false)
 pygobject_dep = dependency('pygobject-3.0', fallback: ['pygobject', 'pygobject_dep'], version : '>= 3.8')
 
 pymod = import('python')

subprojects/gst-python/plugin/gstpythonplugin.c

@@ -25,8 +25,33 @@
 /* include this first, before NO_IMPORT_PYGOBJECT is defined */
 #include <pygobject.h>
 #include <gst/gst.h>
-#include <gmodule.h>
 #include <Python.h>
+/*
+ * We need to call dlopen() directly on macOS to workaround a macOS runtime
+ * linker bug. When there are nested dlopen() calls and the second dlopen() is
+ * called from another library (such as gmodule), @loader_path is resolved as
+ * @executable_path and RPATHs are read from the executable (gst-plugin-scanner)
+ * instead of the library itself (libgstges.dylib). This doesn't happen if the
+ * second dlopen() call is directly in the source code of the library.
+ * Previously seen at:
+ * https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/1171#note_2290789
+ */
+#ifdef G_OS_WIN32
+#include <gmodule.h>
+#define gstpy_module_open(fname) g_module_open(fname,0)
+#define gstpy_module_error g_module_error
+#define gstpy_module_symbol(module,name,symbol) g_module_symbol(module,name,symbol)
+#else
+#include <dlfcn.h>
+#define gstpy_module_open(fname) dlopen(fname,RTLD_NOW | RTLD_GLOBAL)
+#define gstpy_module_error dlerror
+static inline gboolean
+gstpy_module_symbol (gpointer handle, const char *name, gpointer * symbol)
+{
+  *symbol = dlsym (handle, name);
+  return *symbol != NULL;
+}
+#endif
 
 void *_PyGstElement_Type;
 
@@ -214,7 +239,6 @@ plugin_init (GstPlugin * plugin)
   PyGILState_STATE state = 0;
   PyObject *gi, *require_version, *args, *gst, *dict, *pyplugin;
   gboolean we_initialized = FALSE;
-  GModule *libpython;
   gpointer has_python = NULL;
   const gchar *override_path;
 
@@ -229,23 +253,19 @@ plugin_init (GstPlugin * plugin)
       GST_PLUGIN_DEPENDENCY_FLAG_NONE);
 
   GST_LOG ("Checking to see if libpython is already loaded");
-  if (g_module_symbol (g_module_open (NULL, G_MODULE_BIND_LOCAL),
+  if (gstpy_module_symbol (gstpy_module_open (NULL),
           "_Py_NoneStruct", &has_python) && has_python) {
     GST_LOG ("libpython is already loaded");
   } else {
-    const gchar *libpython_path =
-        PY_LIB_LOC "/libpython" PYTHON_VERSION PY_ABI_FLAGS "." PY_LIB_SUFFIX;
-    GST_LOG ("loading libpython from '%s'", libpython_path);
-    libpython = g_module_open (libpython_path, 0);
-    if (!libpython) {
-      g_critical ("Couldn't g_module_open libpython. Reason: %s",
-          g_module_error ());
+    GST_LOG ("loading libpython by name: %s", PY_LIB_FNAME);
+    if (!gstpy_module_open (PY_LIB_FNAME)) {
+      GST_ERROR ("Couldn't load libpython. Reason: %s", gstpy_module_error ());
       return FALSE;
     }
   }
 
   if (!Py_IsInitialized ()) {
-    GST_LOG ("python wasn't initialized");
+    GST_LOG ("python wasn't already initialized");
     /* set the correct plugin for registering stuff */
     Py_Initialize ();
     we_initialized = TRUE;

subprojects/gst-python/plugin/meson.build

@@ -1,7 +1,7 @@
 gstpython = library('gstpython',
     ['gstpythonplugin.c'],
     include_directories : [configinc],
-    dependencies : [gst_dep, pygobject_dep, gstbase_dep, python_dep, gmodule_dep] ,
+    dependencies : [gst_dep, pygobject_dep, gstbase_dep, python_dep, gmodule_dep, libdl],
     install : true,
     install_dir : '@0@/gstreamer-1.0'.format(get_option('libdir')),
 )