Initial flame_lua_runtime package

lib/runtime/lifecycle/runtime_async_gate.dart

@@ -0,0 +1,50 @@
+class RuntimeAsyncGate {
+  RuntimeAsyncGate({bool initiallyClosed = false}) : _closed = initiallyClosed;
+
+  int _generation = 0;
+  bool _closed;
+
+  int get generation => _generation;
+
+  bool get isOpen => !_closed;
+
+  bool get isClosed => _closed;
+
+  RuntimeAsyncToken get token => RuntimeAsyncToken._(this, _generation);
+
+  RuntimeAsyncToken activate() {
+    _closed = false;
+    _generation++;
+    return token;
+  }
+
+  RuntimeAsyncToken advance() {
+    _generation++;
+    return token;
+  }
+
+  RuntimeAsyncToken close() {
+    _closed = true;
+    _generation++;
+    return token;
+  }
+
+  bool accepts(RuntimeAsyncToken token) {
+    return !_closed &&
+        identical(token._gate, this) &&
+        token.generation == _generation;
+  }
+
+  bool acceptsGeneration(int generation) {
+    return !_closed && generation == _generation;
+  }
+}
+
+class RuntimeAsyncToken {
+  const RuntimeAsyncToken._(this._gate, this.generation);
+
+  final RuntimeAsyncGate _gate;
+  final int generation;
+
+  bool get isAccepted => _gate.accepts(this);
+}