context: Start persistent profiling via command line argument

Persistent profiling was started via an env var, but that's rather hard
to discover and remember without grepping; change to use a command line
argument.

The profiler is started early, even during (though late in)
configuration, but configuration should ideally be instant and pointless
to configure.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2998>

src/core/meta-context-main.c

@@ -73,6 +73,7 @@ typedef struct _MetaContextMainOptions
 #ifdef HAVE_NATIVE_BACKEND
   GList *virtual_monitor_infos;
 #endif
+  char *trace_file;
 } MetaContextMainOptions;
 
 struct _MetaContextMain
@@ -298,6 +299,10 @@ meta_context_main_configure (MetaContext   *context,
         context_main->options.sm.client_id = g_strdup (desktop_autostart_id);
     }
 
+#ifdef HAVE_PROFILER
+  meta_context_set_trace_file (context, context_main->options.trace_file);
+#endif
+
   g_unsetenv ("DESKTOP_AUTOSTART_ID");
 
   return TRUE;
@@ -662,6 +667,12 @@ meta_context_main_add_option_entries (MetaContextMain *context_main)
       N_("Run with X11 backend")
     },
 #endif
+    {
+      "profile", 0, 0, G_OPTION_ARG_FILENAME,
+      &context_main->options.trace_file,
+      N_("Profile performance using trace instrumentation"),
+      "FILE"
+    },
     { NULL }
   };
 

src/core/meta-context-private.h

@@ -86,6 +86,9 @@ gboolean meta_context_is_x11_sync (MetaContext *context);
 #ifdef HAVE_PROFILER
 MetaProfiler *
 meta_context_get_profiler (MetaContext *context);
+
+void meta_context_set_trace_file (MetaContext *context,
+                                  const char  *trace_file);
 #endif
 
 #endif /* META_CONTEXT_PRIVATE_H */

src/core/meta-context.c

@@ -98,6 +98,7 @@ typedef struct _MetaContextPrivate
 #endif
 
 #ifdef HAVE_PROFILER
+  char *trace_file;
   MetaProfiler *profiler;
 #endif
 
@@ -292,6 +293,15 @@ meta_context_get_profiler (MetaContext *context)
 
   return priv->profiler;
 }
+
+void
+meta_context_set_trace_file (MetaContext *context,
+                             const char  *trace_file)
+{
+  MetaContextPrivate *priv = meta_context_get_instance_private (context);
+
+  priv->trace_file = g_strdup (trace_file);
+}
 #endif
 
 static gboolean
@@ -343,6 +353,10 @@ meta_context_configure (MetaContext   *context,
       return FALSE;
     }
 
+#ifdef HAVE_PROFILER
+  priv->profiler = meta_profiler_new (priv->trace_file);
+#endif
+
   compositor_type = meta_context_get_compositor_type (context);
   switch (compositor_type)
     {
@@ -739,6 +753,7 @@ meta_context_finalize (GObject *object)
 
 #ifdef HAVE_PROFILER
   g_clear_object (&priv->profiler);
+  g_clear_pointer (&priv->trace_file, g_free);
 #endif
 
   g_clear_pointer (&priv->gnome_wm_keybindings, g_free);
@@ -801,10 +816,6 @@ meta_context_init (MetaContext *context)
   MetaContextPrivate *priv = meta_context_get_instance_private (context);
   g_autoptr (GError) error = NULL;
 
-#ifdef HAVE_PROFILER
-  priv->profiler = meta_profiler_new ();
-#endif
-
   priv->plugin_gtype = G_TYPE_NONE;
   priv->gnome_wm_keybindings = g_strdup ("Mutter");
 

src/core/meta-profiler.c

@@ -265,8 +265,6 @@ meta_profiler_class_init (MetaProfilerClass *klass)
 static void
 meta_profiler_init (MetaProfiler *self)
 {
-  const char *env_trace_file;
-
   g_mutex_init (&self->mutex);
   self->cancellable = g_cancellable_new ();
 
@@ -274,9 +272,16 @@ meta_profiler_init (MetaProfiler *self)
              self->cancellable,
              on_bus_acquired_cb,
              self);
+}
 
-  env_trace_file = g_getenv ("MUTTER_DEBUG_TRACE_FILE");
-  if (env_trace_file && env_trace_file[0])
+MetaProfiler *
+meta_profiler_new (const char *trace_file)
+{
+  MetaProfiler *profiler;
+
+  profiler = g_object_new (META_TYPE_PROFILER, NULL);
+
+  if (trace_file)
     {
       GMainContext *main_context = g_main_context_default ();
       const char *group_name;
@@ -286,15 +291,11 @@ meta_profiler_init (MetaProfiler *self)
 
       cogl_set_tracing_enabled_on_thread (main_context,
                                           group_name,
-                                          env_trace_file);
-      self->persistent = TRUE;
-    }
+                                          trace_file);
+      profiler->persistent = TRUE;
     }
 
-MetaProfiler *
-meta_profiler_new (void)
-{
-  return g_object_new (META_TYPE_PROFILER, NULL);
+  return profiler;
 }
 
 void

src/core/meta-profiler.h

@@ -34,7 +34,7 @@ G_DECLARE_FINAL_TYPE (MetaProfiler,
                       PROFILER,
                       MetaDBusSysprof3ProfilerSkeleton)
 
-MetaProfiler * meta_profiler_new (void);
+MetaProfiler * meta_profiler_new (const char *trace_file);
 
 void meta_profiler_register_thread (MetaProfiler *profiler,
                                     GMainContext *main_context,