Revert AnnotationRegistry to on-demand static (#2476)

src/osgEarth/AnnotationRegistry

@@ -19,8 +19,7 @@
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 */
-#ifndef OSGEARTH_ANNO_REGISTRY_H
-#define OSGEARTH_ANNO_REGISTRY_H 1
+#pragma once
 
 #include <osgEarth/AnnotationNode>
 #include <osgEarth/MapNode>
@@ -108,5 +107,3 @@ namespace osgEarth { namespace Util
     };
 
 } }
-
-#endif // OSGEARTH_ANNO_FEATURE_NODE_H

src/osgEarth/AnnotationRegistry.cpp

@@ -60,10 +60,20 @@ namespace
 AnnotationRegistry*
 AnnotationRegistry::instance()
 {
-    return Registry::instance()->getOrCreate<AnnotationRegistry>(
-        "oe.AnnotationRegistry", []() {
-            return new AnnotationRegistry();
-        });
+    // OK to be in the local scope since this gets called at static init time
+    // by the OSGEARTH_REGISTER_ANNOTATION macro
+    static AnnotationRegistry* s_singleton = nullptr;
+    static std::mutex s_singletonMutex;
+
+    if (!s_singleton)
+    {
+        std::lock_guard<std::mutex> lock(s_singletonMutex);
+        if (!s_singleton)
+        {
+            s_singleton = new AnnotationRegistry();
+        }
+    }
+    return s_singleton;
 }