8005396: Use ParNew with only one thread instead of DefNew as default for CMS...

8005396: Use ParNew with only one thread instead of DefNew as default for CMS on single CPU machines
Reviewed-by: jmasa, jcoomes

src/share/vm/gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.cpp

@@ -56,7 +56,7 @@ void ConcurrentMarkSweepPolicy::initialize_generations() {
   if (_generations == NULL)
     vm_exit_during_initialization("Unable to allocate gen spec");
 
-  if (ParNewGeneration::in_use()) {
+  if (UseParNewGC) {
     if (UseAdaptiveSizePolicy) {
       _generations[0] = new GenerationSpec(Generation::ASParNew,
                                            _initial_gen0_size, _max_gen0_size);
@@ -96,7 +96,7 @@ void ConcurrentMarkSweepPolicy::initialize_size_policy(size_t init_eden_size,
 
 void ConcurrentMarkSweepPolicy::initialize_gc_policy_counters() {
   // initialize the policy counters - 2 collectors, 3 generations
-  if (ParNewGeneration::in_use()) {
+  if (UseParNewGC) {
     _gc_policy_counters = new GCPolicyCounters("ParNew:CMS", 2, 3);
   }
   else {
@@ -119,7 +119,7 @@ void ASConcurrentMarkSweepPolicy::initialize_gc_policy_counters() {
 
   assert(size_policy() != NULL, "A size policy is required");
   // initialize the policy counters - 2 collectors, 3 generations
-  if (ParNewGeneration::in_use()) {
+  if (UseParNewGC) {
     _gc_policy_counters = new CMSGCAdaptivePolicyCounters("ParNew:CMS", 2, 3,
       size_policy());
   }

src/share/vm/gc_implementation/parNew/parNewGeneration.cpp

@@ -1623,7 +1623,3 @@ void ParNewGeneration::ref_processor_init()
 const char* ParNewGeneration::name() const {
   return "par new generation";
 }
-
-bool ParNewGeneration::in_use() {
-  return UseParNewGC && ParallelGCThreads > 0;
-}

src/share/vm/gc_implementation/parNew/parNewGeneration.hpp

@@ -361,8 +361,6 @@ class ParNewGeneration: public DefNewGeneration {
     delete _task_queues;
   }
 
-  static bool in_use();
-
   virtual void ref_processor_init();
   virtual Generation::Name kind()        { return Generation::ParNew; }
   virtual const char* name() const;

src/share/vm/memory/collectorPolicy.cpp

@@ -827,7 +827,7 @@ void MarkSweepPolicy::initialize_generations() {
   if (_generations == NULL)
     vm_exit_during_initialization("Unable to allocate gen spec");
 
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     _generations[0] = new GenerationSpec(Generation::ParNew, _initial_gen0_size, _max_gen0_size);
   } else {
     _generations[0] = new GenerationSpec(Generation::DefNew, _initial_gen0_size, _max_gen0_size);
@@ -840,10 +840,9 @@ void MarkSweepPolicy::initialize_generations() {
 
 void MarkSweepPolicy::initialize_gc_policy_counters() {
   // initialize the policy counters - 2 collectors, 3 generations
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     _gc_policy_counters = new GCPolicyCounters("ParNew:MSC", 2, 3);
-  }
-  else {
+  } else {
     _gc_policy_counters = new GCPolicyCounters("Copy:MSC", 2, 3);
   }
 }

src/share/vm/memory/tenuredGeneration.cpp

@@ -62,7 +62,7 @@ TenuredGeneration::TenuredGeneration(ReservedSpace rs,
                                        _virtual_space.reserved_size(),
                                        _the_space, _gen_counters);
 #ifndef SERIALGC
-  if (UseParNewGC && ParallelGCThreads > 0) {
+  if (UseParNewGC) {
     typedef ParGCAllocBufferWithBOT* ParGCAllocBufferWithBOTPtr;
     _alloc_buffers = NEW_C_HEAP_ARRAY(ParGCAllocBufferWithBOTPtr,
                                       ParallelGCThreads, mtGC);

src/share/vm/runtime/arguments.cpp

@@ -1083,10 +1083,6 @@ static void disable_adaptive_size_policy(const char* collector_name) {
   }
 }
 
-// If the user has chosen ParallelGCThreads > 0, we set UseParNewGC
-// if it's not explictly set or unset. If the user has chosen
-// UseParNewGC and not explicitly set ParallelGCThreads we
-// set it, unless this is a single cpu machine.
 void Arguments::set_parnew_gc_flags() {
   assert(!UseSerialGC && !UseParallelOldGC && !UseParallelGC && !UseG1GC,
          "control point invariant");
@@ -1095,15 +1091,15 @@ void Arguments::set_parnew_gc_flags() {
   // Turn off AdaptiveSizePolicy for parnew until it is complete.
   disable_adaptive_size_policy("UseParNewGC");
 
-  if (ParallelGCThreads == 0) {
-    FLAG_SET_DEFAULT(ParallelGCThreads,
-                     Abstract_VM_Version::parallel_worker_threads());
-    if (ParallelGCThreads == 1) {
-      FLAG_SET_DEFAULT(UseParNewGC, false);
-      FLAG_SET_DEFAULT(ParallelGCThreads, 0);
-    }
+  if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
+    FLAG_SET_DEFAULT(ParallelGCThreads, Abstract_VM_Version::parallel_worker_threads());
+    assert(ParallelGCThreads > 0, "We should always have at least one thread by default");
+  } else if (ParallelGCThreads == 0) {
+    jio_fprintf(defaultStream::error_stream(),
+        "The ParNew GC can not be combined with -XX:ParallelGCThreads=0\n");
+    vm_exit(1);
   }
-  if (UseParNewGC) {
+
   // By default YoungPLABSize and OldPLABSize are set to 4096 and 1024 respectively,
   // these settings are default for Parallel Scavenger. For ParNew+Tenured configuration
   // we set them to 1024 and 1024.
@@ -1130,7 +1126,6 @@ void Arguments::set_parnew_gc_flags() {
     FLAG_SET_DEFAULT(ParGCUseLocalOverflow, true);
   }
   assert(ParGCUseLocalOverflow || !UseCompressedOops, "Error");
-  }
 }
 
 // Adjust some sizes to suit CMS and/or ParNew needs; these work well on