--- old/src/hotspot/share/gc/shared/workgroup.cpp	2020-08-14 16:29:03.953837811 +0200
+++ new/src/hotspot/share/gc/shared/workgroup.cpp	2020-08-14 16:29:03.805835172 +0200
@@ -109,7 +109,7 @@
 //
 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
 // This helps lowering the latency when starting and stopping the worker threads.
-class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
+class GangTaskDispatcher : public CHeapObj<mtGC> {
   // The task currently being dispatched to the GangWorkers.
   AbstractGangTask* _task;
 
@@ -122,7 +122,7 @@
   Semaphore* _end_semaphore;
 
 public:
-  SemaphoreGangTaskDispatcher() :
+  GangTaskDispatcher() :
       _task(NULL),
       _started(0),
       _not_finished(0),
@@ -130,11 +130,15 @@
       _end_semaphore(new Semaphore())
 { }
 
-  ~SemaphoreGangTaskDispatcher() {
+  ~GangTaskDispatcher() {
     delete _start_semaphore;
     delete _end_semaphore;
   }
 
+  // Coordinator API.
+
+  // Distributes the task out to num_workers workers.
+  // Returns when the task has been completed by all workers.
   void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers, bool add_foreground_work) {
     // No workers are allowed to read the state variables until they have been signaled.
     _task         = task;
@@ -155,6 +159,10 @@
 
   }
 
+  // Worker API.
+
+  // Waits for a task to become available to the worker.
+  // Returns when the worker has been assigned a task.
   WorkData worker_wait_for_task() {
     // Wait for the coordinator to dispatch a task.
     _start_semaphore->wait();
@@ -167,6 +175,7 @@
     return WorkData(_task, worker_id);
   }
 
+  // Signal to the coordinator that the worker is done with the assigned task.
   void worker_done_with_task() {
     // Mark that the worker is done with the task.
     // The worker is not allowed to read the state variables after this line.
@@ -184,7 +193,7 @@
                    bool  are_GC_task_threads,
                    bool  are_ConcurrentGC_threads) :
     AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
-    _dispatcher(new SemaphoreGangTaskDispatcher())
+    _dispatcher(new GangTaskDispatcher())
 { }
 
 WorkGang::~WorkGang() {
--- old/src/hotspot/share/gc/shared/workgroup.hpp	2020-08-14 16:29:04.293843872 +0200
+++ new/src/hotspot/share/gc/shared/workgroup.hpp	2020-08-14 16:29:04.117840734 +0200
@@ -52,6 +52,7 @@
 class Semaphore;
 class ThreadClosure;
 class WorkGang;
+class GangTaskDispatcher;
 
 // An abstract task to be worked on by a gang.
 // You subclass this to supply your own work() method
@@ -80,29 +81,6 @@
   WorkData(AbstractGangTask* task, uint worker_id) : _task(task), _worker_id(worker_id) {}
 };
 
-// Interface to handle the synchronization between the coordinator thread and the worker threads,
-// when a task is dispatched out to the worker threads.
-class GangTaskDispatcher : public CHeapObj<mtGC> {
- public:
-  virtual ~GangTaskDispatcher() {}
-
-  // Coordinator API.
-
-  // Distributes the task out to num_workers workers.
-  // Returns when the task has been completed by all workers.
-  virtual void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers,
-                                              bool add_foreground_work) = 0;
-
-  // Worker API.
-
-  // Waits for a task to become available to the worker.
-  // Returns when the worker has been assigned a task.
-  virtual WorkData worker_wait_for_task() = 0;
-
-  // Signal to the coordinator that the worker is done with the assigned task.
-  virtual void     worker_done_with_task() = 0;
-};
-
 // The work gang is the collection of workers to execute tasks.
 // The number of workers run for a task is "_active_workers"
 // while "_total_workers" is the number of available of workers.
--- old/src/hotspot/share/runtime/arguments.cpp	2020-08-14 16:29:04.633849934 +0200
+++ new/src/hotspot/share/runtime/arguments.cpp	2020-08-14 16:29:04.457846796 +0200
@@ -533,7 +533,6 @@
   { "PrintPreciseBiasedLockingStatistics", JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
   { "InitialBootClassLoaderMetaspaceSize", JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
   { "UseLargePagesInMetaspace",            JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
-  { "UseSemaphoreGCThreadsSynchronization", JDK_Version::undefined(), JDK_Version::jdk(16), JDK_Version::jdk(17) },
 
   // --- Deprecated alias flags (see also aliased_jvm_flags) - sorted by obsolete_in then expired_in:
   { "DefaultMaxRAMFraction",        JDK_Version::jdk(8),  JDK_Version::undefined(), JDK_Version::undefined() },
@@ -553,6 +552,7 @@
 #endif
   { "PrintVMQWaitTime",              JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
   { "UseNewFieldLayout",             JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
+  { "UseSemaphoreGCThreadsSynchronization", JDK_Version::undefined(), JDK_Version::jdk(16), JDK_Version::jdk(17) },
 
 #ifdef TEST_VERIFY_SPECIAL_JVM_FLAGS
   // These entries will generate build errors.  Their purpose is to test the macros.