Fix a bug in synchronous model similarity

luprex/core/cpp/globaldb.cpp

@@ -1,8 +1,46 @@
 #include "luastack.hpp"
 #include "globaldb.hpp"
 
+LuaDefine(global_once, "string", "for a given string, returns true exactly once") {
+    LuaArg name;
+    LuaRet flag;
+    LuaVar oncedb, val;
+    LuaStack LS(L, name, flag, oncedb, val);
 
-LuaDefine(global, "globalname", "get a table where global data can be stored") {
+    // Get a pointer to the oncedb.
+    LS.rawget(oncedb, LuaRegistry, "oncedb");
+    if (!LS.istable(oncedb)) {
+        LS.set(flag, false);
+        return LS.result();
+    }
+
+    LS.checkstring(name);
+    LS.rawget(val, oncedb, name);
+    if (!LS.isnil(val)) {
+        LS.set(flag, false);
+        return LS.result();
+    }
+    LS.rawset(oncedb, name, true);
+    LS.set(flag, true);
+    return LS.result();
+}
+
+LuaDefine(global_clearonce, "name", "reset the specified once-flag") {
+    LuaArg name;
+    LuaVar oncedb;
+    LuaStack LS(L, name, oncedb);
+
+    // Get a pointer to the oncedb.
+    LS.rawget(oncedb, LuaRegistry, "oncedb");
+    if (!LS.istable(oncedb)) {
+        return LS.result();
+    }
+    LS.checkstring(name);
+    LS.rawset(oncedb, name, LuaNil);
+    return LS.result();
+}
+
+LuaDefine(global_table, "globalname", "get a table where global data can be stored") {
     LuaArg globalname;
     LuaRet globaltab;
     LuaVar globaldb;