8079275: Remove CollectedHeap::use_parallel_gc_threads

Reviewed-by: sjohanss, kbarrett

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.cpp

@@ -1082,17 +1082,6 @@ size_t CompactibleFreeListSpace::block_size_nopar(const HeapWord* p) const {
 bool CompactibleFreeListSpace::block_is_obj(const HeapWord* p) const {
   FreeChunk* fc = (FreeChunk*)p;
   assert(is_in_reserved(p), "Should be in space");
-  // When doing a mark-sweep-compact of the CMS generation, this
-  // assertion may fail because prepare_for_compaction() uses
-  // space that is garbage to maintain information on ranges of
-  // live objects so that these live ranges can be moved as a whole.
-  // Comment out this assertion until that problem can be solved
-  // (i.e., that the block start calculation may look at objects
-  // at address below "p" in finding the object that contains "p"
-  // and those objects (if garbage) may have been modified to hold
-  // live range information.
-  // assert(CollectedHeap::use_parallel_gc_threads() || _bt.block_start(p) == p,
-  //        "Should be a block boundary");
   if (FreeChunk::indicatesFreeChunk(p)) return false;
   Klass* k = oop(p)->klass_or_null();
   if (k != NULL) {

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp

@@ -225,16 +225,12 @@ ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
            "Offset of FreeChunk::_prev within FreeChunk must match"
            "  that of OopDesc::_klass within OopDesc");
   )
-  if (CollectedHeap::use_parallel_gc_threads()) {
-    typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
-    _par_gc_thread_states =
-      NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
-    for (uint i = 0; i < ParallelGCThreads; i++) {
-      _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
-    }
-  } else {
-    _par_gc_thread_states = NULL;
+
+  _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
+  for (uint i = 0; i < ParallelGCThreads; i++) {
+    _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
   }
+
   _incremental_collection_failed = false;
   // The "dilatation_factor" is the expansion that can occur on
   // account of the fact that the minimum object size in the CMS
@@ -460,7 +456,6 @@ CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
                  -1 /* lock-free */, "No_lock" /* dummy */),
-  _modUnionClosure(&_modUnionTable),
   _modUnionClosurePar(&_modUnionTable),
   // Adjust my span to cover old (cms) gen
   _span(cmsGen->reserved()),
@@ -2130,10 +2125,7 @@ void CMSCollector::gc_prologue(bool full) {
 
   bool registerClosure = duringMarking;
 
-  ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
-                                               &_modUnionClosurePar
-                                               : &_modUnionClosure;
-  _cmsGen->gc_prologue_work(full, registerClosure, muc);
+  _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
 
   if (!full) {
     stats().record_gc0_begin();
@@ -3006,7 +2998,7 @@ void CMSCollector::checkpointRootsInitialWork() {
 
   {
     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
-    if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
+    if (CMSParallelInitialMarkEnabled) {
       // The parallel version.
       FlexibleWorkGang* workers = gch->workers();
       assert(workers != NULL, "Need parallel worker threads.");
@@ -4348,7 +4340,7 @@ void CMSCollector::checkpointRootsFinalWork() {
     // dirtied since the first checkpoint in this GC cycle and prior to
     // the most recent young generation GC, minus those cleaned up by the
     // concurrent precleaning.
-    if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
+    if (CMSParallelRemarkEnabled) {
       GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
       do_remark_parallel();
     } else {

hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp

@@ -647,7 +647,6 @@ class CMSCollector: public CHeapObj<mtGC> {
   // Keep this textually after _markBitMap and _span; c'tor dependency.
 
   ConcurrentMarkSweepThread*     _cmsThread;   // The thread doing the work
-  ModUnionClosure    _modUnionClosure;
   ModUnionClosurePar _modUnionClosurePar;
 
   // CMS abstract state machine

hotspot/src/share/vm/gc_interface/collectedHeap.hpp

@@ -598,13 +598,6 @@ class CollectedHeap : public CHeapObj<mtInternal> {
 #endif
 
  public:
-  // This is a convenience method that is used in cases where
-  // the actual number of GC worker threads is not pertinent but
-  // only whether there more than 0.  Use of this method helps
-  // reduce the occurrence of ParallelGCThreads to uses where the
-  // actual number may be germane.
-  static bool use_parallel_gc_threads() { return ParallelGCThreads > 0; }
-
   // Copy the current allocation context statistics for the specified contexts.
   // For each context in contexts, set the corresponding entries in the totals
   // and accuracy arrays to the current values held by the statistics.  Each

hotspot/src/share/vm/memory/genCollectedHeap.cpp

@@ -640,7 +640,7 @@ void GenCollectedHeap::process_roots(bool activate_scope,
   // All threads execute the following. A specific chunk of buckets
   // from the StringTable are the individual tasks.
   if (weak_roots != NULL) {
-    if (CollectedHeap::use_parallel_gc_threads()) {
+    if (is_par) {
       StringTable::possibly_parallel_oops_do(weak_roots);
     } else {
       StringTable::oops_do(weak_roots);