8040807: G1: Enable G1CollectedHeap::stop()

Reviewed-by: brutisso, jmasa, tschatzl

hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -901,7 +901,7 @@ void ConcurrentMark::checkpointRootsInitialPre() {
   G1CollectedHeap*   g1h = G1CollectedHeap::heap();
   G1CollectorPolicy* g1p = g1h->g1_policy();
 
-  _has_aborted = false;
+  clear_has_aborted();
 
 #ifndef PRODUCT
   if (G1PrintReachableAtInitialMark) {
@@ -3261,7 +3261,7 @@ void ConcurrentMark::abort() {
   }
   _first_overflow_barrier_sync.abort();
   _second_overflow_barrier_sync.abort();
-  _has_aborted = true;
+  set_has_aborted();
 
   SATBMarkQueueSet& satb_mq_set = JavaThread::satb_mark_queue_set();
   satb_mq_set.abandon_partial_marking();

hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp

@@ -822,7 +822,9 @@ public:
   // Called to abort the marking cycle after a Full GC takes place.
   void abort();
 
-  bool has_aborted()      { return _has_aborted; }
+  bool has_aborted()       { return _has_aborted; }
+  void set_has_aborted()   { _has_aborted = true; }
+  void clear_has_aborted() { _has_aborted = false; }
 
   // This prints the global/local fingers. It is used for debugging.
   NOT_PRODUCT(void print_finger();)

hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -2174,20 +2174,14 @@ jint G1CollectedHeap::initialize() {
 }
 
 void G1CollectedHeap::stop() {
-#if 0
-  // Stopping concurrent worker threads is currently disabled until
-  // some bugs in concurrent mark has been resolve. Without fixing
-  // those bugs first we risk haning during VM exit when trying to
-  // stop these threads.
-
-  // Abort any ongoing concurrent root region scanning and stop all
-  // concurrent threads. We do this to make sure these threads do
-  // not continue to execute and access resources (e.g. gclog_or_tty)
-  // that are destroyed during shutdown.
+  // Abort any ongoing concurrent mark and stop all concurrent threads.
+  // We do this to make sure these threads do not continue to execute
+  // and access resources (e.g. gclog_or_tty) that are destroyed during
+  // shutdown.
+  _cm->set_has_aborted();
   _cm->root_regions()->abort();
   _cm->root_regions()->wait_until_scan_finished();
   stop_conc_gc_threads();
-#endif
 }
 
 size_t G1CollectedHeap::conservative_max_heap_alignment() {

hotspot/src/share/vm/runtime/java.cpp

@@ -501,9 +501,6 @@ void before_exit(JavaThread * thread) {
     os::infinite_sleep();
   }
 
-  // Stop any ongoing concurrent GC work
-  Universe::heap()->stop();
-
   // Terminate watcher thread - must before disenrolling any periodic task
   if (PeriodicTask::num_tasks() > 0)
     WatcherThread::stop();
@@ -518,10 +515,8 @@ void before_exit(JavaThread * thread) {
   StatSampler::disengage();
   StatSampler::destroy();
 
-  // We do not need to explicitly stop concurrent GC threads because the
-  // JVM will be taken down at a safepoint when such threads are inactive --
-  // except for some concurrent G1 threads, see (comment in)
-  // Threads::destroy_vm().
+  // Stop concurrent GC threads
+  Universe::heap()->stop();
 
   // Print GC/heap related information.
   if (PrintGCDetails) {

hotspot/src/share/vm/runtime/thread.cpp

@@ -3966,14 +3966,8 @@ bool Threads::destroy_vm() {
     // GC vm_operations can get caught at the safepoint, and the
     // heap is unparseable if they are caught. Grab the Heap_lock
     // to prevent this. The GC vm_operations will not be able to
-    // queue until after the vm thread is dead.
-    // After this point, we'll never emerge out of the safepoint before
-    // the VM exits, so concurrent GC threads do not need to be explicitly
-    // stopped; they remain inactive until the process exits.
-    // Note: some concurrent G1 threads may be running during a safepoint,
-    // but these will not be accessing the heap, just some G1-specific side
-    // data structures that are not accessed by any other threads but them
-    // after this point in a terminal safepoint.
+    // queue until after the vm thread is dead. After this point,
+    // we'll never emerge out of the safepoint before the VM exits.
 
     MutexLocker ml(Heap_lock);