diff a/src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.hpp b/src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.hpp
--- /dev/null
+++ b/src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.hpp
@@ -0,0 +1,129 @@
+/*
+ * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
+ * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_GC_SHENANDOAH_SHENANDOAHGENERATIONALCONTROLTHREAD_HPP
+#define SHARE_GC_SHENANDOAH_SHENANDOAHGENERATIONALCONTROLTHREAD_HPP
+
+#include "gc/shared/gcCause.hpp"
+#include "gc/shenandoah/shenandoahController.hpp"
+#include "gc/shenandoah/shenandoahGenerationType.hpp"
+#include "gc/shenandoah/shenandoahGC.hpp"
+#include "gc/shenandoah/shenandoahPadding.hpp"
+#include "gc/shenandoah/shenandoahSharedVariables.hpp"
+
+class ShenandoahOldGeneration;
+class ShenandoahGeneration;
+class ShenandoahGenerationalHeap;
+class ShenandoahHeap;
+
+class ShenandoahGenerationalControlThread: public ShenandoahController {
+  friend class VMStructs;
+
+public:
+  typedef enum {
+    none,
+    concurrent_normal,
+    stw_degenerated,
+    stw_full,
+    bootstrapping_old,
+    servicing_old
+  } GCMode;
+
+private:
+  Monitor _control_lock;
+  Monitor _regulator_lock;
+
+  ShenandoahSharedFlag _allow_old_preemption;
+  ShenandoahSharedFlag _preemption_requested;
+
+  GCCause::Cause  _requested_gc_cause;
+  volatile ShenandoahGenerationType _requested_generation;
+  ShenandoahGC::ShenandoahDegenPoint _degen_point;
+  ShenandoahGeneration* _degen_generation;
+
+  shenandoah_padding(0);
+  volatile GCMode _mode;
+  shenandoah_padding(1);
+
+public:
+  ShenandoahGenerationalControlThread();
+
+  void run_service() override;
+  void stop_service() override;
+
+  void request_gc(GCCause::Cause cause) override;
+
+  // Return true if the request to start a concurrent GC for the given generation succeeded.
+  bool request_concurrent_gc(ShenandoahGenerationType generation);
+
+  GCMode gc_mode() {
+    return _mode;
+  }
+private:
+
+  // Returns true if the cycle has been cancelled or degenerated.
+  bool check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point);
+
+  // Returns true if the old generation marking completed (i.e., final mark executed for old generation).
+  bool resume_concurrent_old_cycle(ShenandoahOldGeneration* generation, GCCause::Cause cause);
+  void service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool reset_old_bitmap_specially);
+  void service_stw_full_cycle(GCCause::Cause cause);
+  void service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point);
+
+  void notify_gc_waiters();
+
+  // Handle GC request.
+  // Blocks until GC is over.
+  void handle_requested_gc(GCCause::Cause cause);
+
+  bool is_explicit_gc(GCCause::Cause cause) const;
+  bool is_implicit_gc(GCCause::Cause cause) const;
+
+  // Returns true if the old generation marking was interrupted to allow a young cycle.
+  bool preempt_old_marking(ShenandoahGenerationType generation);
+
+  void process_phase_timings(const ShenandoahGenerationalHeap* heap);
+
+  void service_concurrent_normal_cycle(ShenandoahGenerationalHeap* heap,
+                                       ShenandoahGenerationType generation,
+                                       GCCause::Cause cause);
+
+  void service_concurrent_old_cycle(ShenandoahGenerationalHeap* heap,
+                                    GCCause::Cause &cause);
+
+  void set_gc_mode(GCMode new_mode);
+
+  static const char* gc_mode_name(GCMode mode);
+
+  void notify_control_thread();
+
+  void service_concurrent_cycle(ShenandoahHeap* heap,
+                                ShenandoahGeneration* generation,
+                                GCCause::Cause &cause,
+                                bool do_old_gc_bootstrap);
+
+};
+
+#endif // SHARE_GC_SHENANDOAH_SHENANDOAHGENERATIONALCONTROLTHREAD_HPP
