From 7566ad6d188b9f40b828dae1d814bcdd54967d25 Mon Sep 17 00:00:00 2001
Date: Tue, 16 Mar 2021 06:02:47 +0000
Subject: [PATCH 2/3] backport JDK-8214535 to support Jmap parallel

---
 .../gc_implementation/g1/g1CollectedHeap.cpp  |  30 ++++++
 .../gc_implementation/g1/g1CollectedHeap.hpp  |   7 +-
 .../vm/gc_implementation/g1/heapRegion.hpp    |   3 +-
 .../parallelScavenge/parallelScavengeHeap.cpp |  75 ++++++++++++-
 .../parallelScavenge/parallelScavengeHeap.hpp |   9 +-
 .../parallelScavenge/psOldGen.cpp             |  29 +++++
 .../parallelScavenge/psOldGen.hpp             |  11 ++
 .../shared/vmGCOperations.cpp                 |   2 +-
 .../shared/vmGCOperations.hpp                 |   4 +-
 .../share/vm/gc_interface/collectedHeap.hpp   |  19 +++-
 .../src/share/vm/memory/genCollectedHeap.cpp  |   4 +
 .../src/share/vm/memory/genCollectedHeap.hpp  |   3 +-
 .../src/share/vm/memory/heapInspection.cpp    | 102 ++++++++++++++++--
 .../src/share/vm/memory/heapInspection.hpp    |  46 +++++++-
 hotspot/src/share/vm/runtime/arguments.hpp    |  12 +--
 .../src/share/vm/services/attachListener.cpp  |  13 ++-
 hotspot/src/share/vm/utilities/workgroup.hpp  |  21 +++-
 .../share/classes/sun/tools/jmap/JMap.java    |  39 +++++--
 jdk/test/sun/tools/common/ApplicationSetup.sh |  12 ++-
 jdk/test/sun/tools/jmap/ParallelInspection.sh |  79 ++++++++++++++
 22 files changed, 480 insertions(+), 45 deletions(-)
 create mode 100644 jdk/test/sun/tools/jmap/ParallelInspection.sh

diff --git a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
index 47d8000a..5cb13535 100644
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp
@@ -59,6 +59,7 @@
 #include "gc_implementation/shared/gcTraceTime.hpp"
 #include "gc_implementation/shared/isGCActiveMark.hpp"
 #include "memory/allocation.hpp"
+#include "memory/heapInspection.hpp"
 #include "memory/gcLocker.inline.hpp"
 #include "memory/generationSpec.hpp"
 #include "memory/iterator.hpp"
@@ -381,6 +382,11 @@ void G1RegionMappingChangedListener::on_commit(uint start_idx, size_t num_region
   reset_from_card_cache(start_idx, num_regions);
 }
 
+void G1CollectedHeap::run_task(AbstractGangTask* task) {
+    workers()->run_task(task);
+    reset_heap_region_claim_values();
+}
+
 void G1CollectedHeap::push_dirty_cards_region(HeapRegion* hr)
 {
   // Claim the right to put the region on the dirty cards region list
@@ -2647,6 +2653,30 @@ void G1CollectedHeap::object_iterate(ObjectClosure* cl) {
   heap_region_iterate(&blk);
 }
 
+class G1ParallelObjectIterator : public ParallelObjectIterator {
+private:
+    G1CollectedHeap*  _heap;
+    uint _num_threads;
+
+public:
+    G1ParallelObjectIterator(uint thread_num) :
+        _heap(G1CollectedHeap::heap()),_num_threads(thread_num) {}
+
+    virtual void object_iterate(ObjectClosure* cl, uint worker_id) {
+        _heap->object_iterate_parallel(cl, worker_id,_num_threads);
+    }
+};
+
+ParallelObjectIterator* G1CollectedHeap::parallel_object_iterator(uint thread_num) {
+    return new G1ParallelObjectIterator(thread_num);
+}
+
+void G1CollectedHeap::object_iterate_parallel(ObjectClosure* cl, uint worker_id, uint num_workers) {
+    IterateObjectClosureRegionClosure blk(cl);
+    heap_region_par_iterate_chunked(&blk, worker_id, num_workers, HeapRegion::ParInspectClaimValue);
+}
+
+
 // Calls a SpaceClosure on a HeapRegion.
 
 class SpaceClosureRegionClosure: public HeapRegionClosure {
diff --git a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
index bde0ca4d..f8c52e68 100644
--- a/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
+++ b/hotspot/src/share/vm/gc_implementation/g1/g1CollectedHeap.hpp
@@ -646,6 +646,8 @@ public:
   G1Allocator* allocator() {
     return _allocator;
   }
+  // Runs the given AbstractGangTask with the current active workers.
+  virtual void run_task(AbstractGangTask* task);
 
   G1MonitoringSupport* g1mm() {
     assert(_g1mm != NULL, "should have been initialized");
@@ -1292,6 +1294,7 @@ public:
   void cleanUpCardTable();
 
   // Iteration functions.
+  void object_iterate_parallel(ObjectClosure* cl, uint worker_id, uint num_workers);
 
   // Iterate over all the ref-containing fields of all objects, calling
   // "cl.do_oop" on each.
@@ -1299,7 +1302,7 @@ public:
 
   // Iterate over all objects, calling "cl.do_object" on each.
   virtual void object_iterate(ObjectClosure* cl);
-
+  virtual ParallelObjectIterator* parallel_object_iterator(uint thread_num);
   virtual void safe_object_iterate(ObjectClosure* cl) {
     object_iterate(cl);
   }
@@ -1607,7 +1610,7 @@ public:
 
   // Perform any cleanup actions necessary before allowing a verification.
   virtual void prepare_for_verify();
-
+  virtual FlexibleWorkGang* get_safepoint_workers() { return _workers; }
   // Perform verification.
 
   // vo == UsePrevMarking  -> use "prev" marking information,
diff --git a/hotspot/src/share/vm/gc_implementation/g1/heapRegion.hpp b/hotspot/src/share/vm/gc_implementation/g1/heapRegion.hpp
index c16c906e..b58a3cc2 100644
--- a/hotspot/src/share/vm/gc_implementation/g1/heapRegion.hpp
+++ b/hotspot/src/share/vm/gc_implementation/g1/heapRegion.hpp
@@ -347,7 +347,8 @@ class HeapRegion: public G1OffsetTableContigSpace {
     ParEvacFailureClaimValue   = 6,
     AggregateCountClaimValue   = 7,
     VerifyCountClaimValue      = 8,
-    ParMarkRootClaimValue      = 9
+    ParMarkRootClaimValue      = 9,
+    ParInspectClaimValue       = 10
   };
 
   // All allocated blocks are occupied by objects in a HeapRegion
diff --git a/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp b/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp
index e13fefa2..cf281259 100644
--- a/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp
+++ b/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp
@@ -60,7 +60,12 @@ jint ParallelScavengeHeap::initialize() {
   _collector_policy->initialize_all();
 
   const size_t heap_size = _collector_policy->max_heap_byte_size();
-
+  _workers = new FlexibleWorkGang("GC Thread",ParallelGCThreads, true, false);
+  if (_workers == NULL) {
+      vm_exit_during_initialization("Failed necessary allocation.");
+  } else {
+      _workers->initialize_workers();
+  }
   ReservedSpace heap_rs = Universe::reserve_heap(heap_size, _collector_policy->heap_alignment());
   MemTracker::record_virtual_memory_type((address)heap_rs.base(), mtJavaHeap);
 
@@ -547,6 +552,71 @@ void ParallelScavengeHeap::object_iterate(ObjectClosure* cl) {
   old_gen()->object_iterate(cl);
 }
 
+// The HeapBlockClaimer is used during parallel iteration over the heap,
+// allowing workers to claim heap areas ("blocks"), gaining exclusive rights to these.
+// The eden and survivor spaces are treated as single blocks as it is hard to divide
+// these spaces.
+// The old space is divided into fixed-size blocks.
+class HeapBlockClaimer : public StackObj {
+    size_t _claimed_index;
+
+public:
+    static const size_t InvalidIndex = SIZE_MAX;
+    static const size_t EdenIndex = 0;
+    static const size_t SurvivorIndex = 1;
+    static const size_t NumNonOldGenClaims = 2;
+
+    HeapBlockClaimer() : _claimed_index(EdenIndex) { }
+    // Claim the block and get the block index.
+    size_t claim_and_get_block() {
+      size_t block_index;
+      block_index = Atomic::add(1u, reinterpret_cast<volatile jint *>(&_claimed_index)) - 1;
+
+      PSOldGen* old_gen = ParallelScavengeHeap::heap()->old_gen();
+      size_t num_claims = old_gen->num_iterable_blocks() + NumNonOldGenClaims;
+
+      return block_index < num_claims ? block_index : InvalidIndex;
+    }
+};
+
+void ParallelScavengeHeap::object_iterate_parallel(ObjectClosure* cl,
+                                                   HeapBlockClaimer* claimer) {
+  size_t block_index = claimer->claim_and_get_block();
+  // Iterate until all blocks are claimed
+  if (block_index == HeapBlockClaimer::EdenIndex) {
+    young_gen()->eden_space()->object_iterate(cl);
+    block_index = claimer->claim_and_get_block();
+  }
+  if (block_index == HeapBlockClaimer::SurvivorIndex) {
+    young_gen()->from_space()->object_iterate(cl);
+    young_gen()->to_space()->object_iterate(cl);
+    block_index = claimer->claim_and_get_block();
+  }
+  while (block_index != HeapBlockClaimer::InvalidIndex) {
+    old_gen()->object_iterate_block(cl, block_index - HeapBlockClaimer::NumNonOldGenClaims);
+    block_index = claimer->claim_and_get_block();
+  }
+}
+
+class PSScavengeParallelObjectIterator : public ParallelObjectIterator {
+private:
+    ParallelScavengeHeap*  _heap;
+    HeapBlockClaimer      _claimer;
+
+public:
+    PSScavengeParallelObjectIterator() :
+            _heap(ParallelScavengeHeap::heap()),
+            _claimer() {}
+
+    virtual void object_iterate(ObjectClosure* cl, uint worker_id) {
+      _heap->object_iterate_parallel(cl, &_claimer);
+    }
+};
+
+ParallelObjectIterator* ParallelScavengeHeap::parallel_object_iterator(uint thread_num) {
+  return new PSScavengeParallelObjectIterator();
+}
+
 
 HeapWord* ParallelScavengeHeap::block_start(const void* addr) const {
   if (young_gen()->is_in_reserved(addr)) {
@@ -622,6 +692,9 @@ void ParallelScavengeHeap::print_on_error(outputStream* st) const {
 void ParallelScavengeHeap::gc_threads_do(ThreadClosure* tc) const {
   PSScavenge::gc_task_manager()->threads_do(tc);
 }
+void ParallelScavengeHeap::run_task(AbstractGangTask* task) {
+  _workers->run_task(task);
+}
 
 void ParallelScavengeHeap::print_gc_threads_on(outputStream* st) const {
   PSScavenge::gc_task_manager()->print_threads_on(st);
diff --git a/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp b/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp
index bf3a207c..96244cb4 100644
--- a/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp
+++ b/hotspot/src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.hpp
@@ -41,6 +41,7 @@ class GCHeapSummary;
 class GCTaskManager;
 class PSAdaptiveSizePolicy;
 class PSHeapSummary;
+class HeapBlockClaimer;
 
 class ParallelScavengeHeap : public CollectedHeap {
   friend class VMStructs;
@@ -55,7 +56,7 @@ class ParallelScavengeHeap : public CollectedHeap {
   static ParallelScavengeHeap* _psh;
 
   GenerationSizer* _collector_policy;
-
+  FlexibleWorkGang* _workers;
   // Collection of generations that are adjacent in the
   // space reserved for the heap.
   AdjoiningGenerations* _gens;
@@ -208,7 +209,9 @@ class ParallelScavengeHeap : public CollectedHeap {
   void oop_iterate(ExtendedOopClosure* cl);
   void object_iterate(ObjectClosure* cl);
   void safe_object_iterate(ObjectClosure* cl) { object_iterate(cl); }
-
+  void object_iterate_parallel(ObjectClosure* cl, HeapBlockClaimer* claimer);
+  virtual ParallelObjectIterator* parallel_object_iterator(uint thread_num);
+  virtual FlexibleWorkGang* get_safepoint_workers() { return _workers; }
   HeapWord* block_start(const void* addr) const;
   size_t block_size(const HeapWord* addr) const;
   bool block_is_obj(const HeapWord* addr) const;
@@ -222,7 +225,7 @@ class ParallelScavengeHeap : public CollectedHeap {
   virtual void print_gc_threads_on(outputStream* st) const;
   virtual void gc_threads_do(ThreadClosure* tc) const;
   virtual void print_tracing_info() const;
-
+  virtual void run_task(AbstractGangTask* task);
   void verify(bool silent, VerifyOption option /* ignored */);
 
   void print_heap_change(size_t prev_used);
diff --git a/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp b/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp
index 12d0d450..dd652553 100644
--- a/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp
+++ b/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.cpp
@@ -206,6 +206,35 @@ HeapWord* PSOldGen::allocate(size_t word_size) {
   return res;
 }
 
+size_t PSOldGen::num_iterable_blocks() const {
+  return (object_space()->used_in_bytes() + IterateBlockSize - 1) / IterateBlockSize;
+}
+
+void PSOldGen::object_iterate_block(ObjectClosure* cl, size_t block_index) {
+  size_t block_word_size = IterateBlockSize / HeapWordSize;
+  assert((block_word_size % (ObjectStartArray::block_size)) == 0,
+         "Block size not a multiple of start_array block");
+
+  MutableSpace *space = object_space();
+
+  HeapWord* begin = space->bottom() + block_index * block_word_size;
+  HeapWord* end = MIN2(space->top(), begin + block_word_size);
+
+  if (!start_array()->object_starts_in_range(begin, end)) {
+    return;
+  }
+
+  // Get object starting at or reaching into this block.
+  HeapWord* start = start_array()->object_start(begin);
+  if (start < begin) {
+    start += oop(start)->size();
+  }
+  // Iterate all objects until the end.
+  for (HeapWord* p = start; p < end; p += oop(p)->size()) {
+    cl->do_object(oop(p));
+  }
+}
+
 HeapWord* PSOldGen::expand_and_allocate(size_t word_size) {
   expand(word_size*HeapWordSize);
   if (GCExpandToAllocateDelayMillis > 0) {
diff --git a/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp b/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp
index 90fa0d56..73738b95 100644
--- a/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp
+++ b/hotspot/src/share/vm/gc_implementation/parallelScavenge/psOldGen.hpp
@@ -57,6 +57,9 @@ class PSOldGen : public CHeapObj<mtGC> {
   const size_t _min_gen_size;
   const size_t _max_gen_size;
 
+  // Block size for parallel iteration
+  static const size_t IterateBlockSize = 1024 * 1024;
+
   // Used when initializing the _name field.
   static inline const char* select_name();
 
@@ -170,6 +173,14 @@ class PSOldGen : public CHeapObj<mtGC> {
   void oop_iterate_no_header(OopClosure* cl) { object_space()->oop_iterate_no_header(cl); }
   void object_iterate(ObjectClosure* cl) { object_space()->object_iterate(cl); }
 
+  // Number of blocks to be iterated over in the used part of old gen.
+  size_t num_iterable_blocks() const;
+  // Iterate the objects starting in block block_index within [bottom, top) of the
+  // old gen. The object just reaching into this block is not iterated over.
+  // A block is an evenly sized non-overlapping part of the old gen of
+  // IterateBlockSize bytes.
+  void object_iterate_block(ObjectClosure* cl, size_t block_index);
+
   // Debugging - do not use for time critical operations
   virtual void print() const;
   virtual void print_on(outputStream* st) const;
diff --git a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
index 85059b82..d086a56c 100644
--- a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
+++ b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.cpp
@@ -188,7 +188,7 @@ void VM_GC_HeapInspection::doit() {
   }
   HeapInspection inspect(_csv_format, _print_help, _print_class_stats,
                          _columns);
-  inspect.heap_inspection(_out);
+  inspect.heap_inspection(_out, _parallel_thread_num);
 }
 
 
diff --git a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.hpp b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.hpp
index cb070bd7..10d37522 100644
--- a/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.hpp
+++ b/hotspot/src/share/vm/gc_implementation/shared/vmGCOperations.hpp
@@ -132,18 +132,20 @@ class VM_GC_HeapInspection: public VM_GC_Operation {
  private:
   outputStream* _out;
   bool _full_gc;
+  uint _parallel_thread_num;
   bool _csv_format; // "comma separated values" format for spreadsheet.
   bool _print_help;
   bool _print_class_stats;
   const char* _columns;
  public:
-  VM_GC_HeapInspection(outputStream* out, bool request_full_gc) :
+  VM_GC_HeapInspection(outputStream* out, bool request_full_gc, uint parallel_thread_num = 1) :
     VM_GC_Operation(0 /* total collections,      dummy, ignored */,
                     GCCause::_heap_inspection /* GC Cause */,
                     0 /* total full collections, dummy, ignored */,
                     request_full_gc) {
     _out = out;
     _full_gc = request_full_gc;
+    _parallel_thread_num = parallel_thread_num;
     _csv_format = false;
     _print_help = false;
     _print_class_stats = false;
diff --git a/hotspot/src/share/vm/gc_interface/collectedHeap.hpp b/hotspot/src/share/vm/gc_interface/collectedHeap.hpp
index 88632ddc..7af75fd6 100644
--- a/hotspot/src/share/vm/gc_interface/collectedHeap.hpp
+++ b/hotspot/src/share/vm/gc_interface/collectedHeap.hpp
@@ -25,6 +25,7 @@
 #ifndef SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
 #define SHARE_VM_GC_INTERFACE_COLLECTEDHEAP_HPP
 
+#include "utilities/workgroup.hpp"
 #include "gc_interface/gcCause.hpp"
 #include "gc_implementation/shared/gcWhen.hpp"
 #include "memory/allocation.hpp"
@@ -38,7 +39,7 @@
 // is an abstract class: there may be many different kinds of heaps.  This
 // class defines the functions that a heap must implement, and contains
 // infrastructure common to all heaps.
-
+class AbstractGangTask;
 class AdaptiveSizePolicy;
 class BarrierSet;
 class CollectorPolicy;
@@ -74,6 +75,12 @@ class GCHeapLog : public EventLogBase<GCMessage> {
   }
 };
 
+class ParallelObjectIterator : public CHeapObj<mtGC> {
+public:
+    virtual void object_iterate(ObjectClosure* cl, uint worker_id) = 0;
+};
+
+
 //
 // CollectedHeap
 //   SharedHeap
@@ -461,7 +468,7 @@ class CollectedHeap : public CHeapObj<mtInternal> {
 
   // Does this heap support heap inspection (+PrintClassHistogram?)
   virtual bool supports_heap_inspection() const = 0;
-
+  virtual FlexibleWorkGang* get_safepoint_workers() { return NULL; }
   // Perform a collection of the heap; intended for use in implementing
   // "System.gc".  This probably implies as full a collection as the
   // "CollectedHeap" supports.
@@ -514,7 +521,10 @@ class CollectedHeap : public CHeapObj<mtInternal> {
   // Iterate over all objects, calling "cl.do_object" on each.
   virtual void object_iterate(ObjectClosure* cl) = 0;
 
-  // Similar to object_iterate() except iterates only
+  virtual ParallelObjectIterator* parallel_object_iterator(uint thread_num) {
+      return NULL;
+  }
+
   // over live objects.
   virtual void safe_object_iterate(ObjectClosure* cl) = 0;
 
@@ -593,6 +603,9 @@ class CollectedHeap : public CHeapObj<mtInternal> {
   // Iterator for all GC threads (other than VM thread)
   virtual void gc_threads_do(ThreadClosure* tc) const = 0;
 
+  // Run given task. Possibly in parallel if the GC supports it.
+  virtual void run_task(AbstractGangTask* task) = 0;
+
   // Print any relevant tracing info that flags imply.
   // Default implementation does nothing.
   virtual void print_tracing_info() const = 0;
diff --git a/hotspot/src/share/vm/memory/genCollectedHeap.cpp b/hotspot/src/share/vm/memory/genCollectedHeap.cpp
index bbe6370a..ed2c0afb 100644
--- a/hotspot/src/share/vm/memory/genCollectedHeap.cpp
+++ b/hotspot/src/share/vm/memory/genCollectedHeap.cpp
@@ -1414,3 +1414,7 @@ void GenCollectedHeap::stop() {
   }
 #endif
 }
+
+void GenCollectedHeap::run_task(AbstractGangTask *task) {
+
+}
diff --git a/hotspot/src/share/vm/memory/genCollectedHeap.hpp b/hotspot/src/share/vm/memory/genCollectedHeap.hpp
index 6d0dd591..2c78ea15 100644
--- a/hotspot/src/share/vm/memory/genCollectedHeap.hpp
+++ b/hotspot/src/share/vm/memory/genCollectedHeap.hpp
@@ -120,6 +120,7 @@ public:
 
   // Returns JNI_OK on success
   virtual jint initialize();
+
   char* allocate(size_t alignment,
                  size_t* _total_reserved, int* _n_covered_regions,
                  ReservedSpace* heap_rs);
@@ -229,7 +230,7 @@ public:
   // may not pack objects densely; a chunk may either be an object or a
   // non-object.
   virtual HeapWord* block_start(const void* addr) const;
-
+  virtual void run_task(AbstractGangTask* task);
   // Requires "addr" to be the start of a chunk, and returns its size.
   // "addr + size" is required to be the start of a new chunk, or the end
   // of the active area of the heap. Assumes (and verifies in non-product
diff --git a/hotspot/src/share/vm/memory/heapInspection.cpp b/hotspot/src/share/vm/memory/heapInspection.cpp
index cc8f4fc0..7c44c50f 100644
--- a/hotspot/src/share/vm/memory/heapInspection.cpp
+++ b/hotspot/src/share/vm/memory/heapInspection.cpp
@@ -28,6 +28,7 @@
 #include "memory/genCollectedHeap.hpp"
 #include "memory/heapInspection.hpp"
 #include "memory/resourceArea.hpp"
+#include "runtime/atomic.hpp"
 #include "runtime/os.hpp"
 #include "utilities/globalDefinitions.hpp"
 #include "utilities/macros.hpp"
@@ -200,6 +201,41 @@ size_t KlassInfoTable::size_of_instances_in_words() const {
   return _size_of_instances_in_words;
 }
 
+// Return false if the entry could not be recorded on account
+// of running out of space required to create a new entry.
+bool KlassInfoTable::merge_entry(const KlassInfoEntry* cie) {
+    Klass*          k = cie->klass();
+    KlassInfoEntry* elt = lookup(k);
+    // elt may be NULL if it's a new klass for which we
+    // could not allocate space for a new entry in the hashtable.
+    if (elt != NULL) {
+        elt->set_count(elt->count() + cie->count());
+        elt->set_words(elt->words() + cie->words());
+        _size_of_instances_in_words += cie->words();
+        return true;
+    }
+    return false;
+}
+
+class KlassInfoTableMergeClosure : public KlassInfoClosure {
+private:
+    KlassInfoTable* _dest;
+    bool _success;
+public:
+    KlassInfoTableMergeClosure(KlassInfoTable* table) : _dest(table), _success(true) {}
+    void do_cinfo(KlassInfoEntry* cie) {
+        _success &= _dest->merge_entry(cie);
+    }
+    bool success() { return _success; }
+};
+
+// merge from table
+bool KlassInfoTable::merge(KlassInfoTable* table) {
+    KlassInfoTableMergeClosure closure(this);
+    table->iterate(&closure);
+    return closure.success();
+}
+
 int KlassInfoHisto::sort_helper(KlassInfoEntry** e1, KlassInfoEntry** e2) {
   return (*e1)->compare(*e1,*e2);
 }
@@ -461,7 +497,7 @@ class HistoClosure : public KlassInfoClosure {
 class RecordInstanceClosure : public ObjectClosure {
  private:
   KlassInfoTable* _cit;
-  size_t _missed_count;
+  uintx _missed_count;
   BoolObjectClosure* _filter;
  public:
   RecordInstanceClosure(KlassInfoTable* cit, BoolObjectClosure* filter) :
@@ -475,7 +511,7 @@ class RecordInstanceClosure : public ObjectClosure {
     }
   }
 
-  size_t missed_count() { return _missed_count; }
+  uintx missed_count() { return _missed_count; }
 
  private:
   bool should_visit(oop obj) {
@@ -483,17 +519,67 @@ class RecordInstanceClosure : public ObjectClosure {
   }
 };
 
-size_t HeapInspection::populate_table(KlassInfoTable* cit, BoolObjectClosure *filter) {
-  ResourceMark rm;
+// Heap inspection for every worker.
+// When native OOM hanppens for KlassInfoTable, set _success to false.
+void ParHeapInspectTask::work(uint worker_id) {
+    uintx missed_count = 0;
+    bool merge_success = true;
+    if (!Atomic::load(reinterpret_cast<jlong *>(&_success))) {
+        // other worker has failed on parallel iteration.
+        return;
+    }
+    KlassInfoTable cit(false);
+    if (cit.allocation_failed()) {
+        // fail to allocate memory, stop parallel mode
+        Atomic::store(false, reinterpret_cast<jlong *>(&_success));
+        return;
+    }
+    RecordInstanceClosure ric(&cit, _filter);
+    _poi->object_iterate(&ric, worker_id);
+    missed_count = ric.missed_count();
+    {
+        MutexLocker x(&_mutex);
+        merge_success = _shared_cit->merge(&cit);
+    }
+    if (merge_success) {
+        Atomic::add(missed_count, reinterpret_cast<jlong *>(&missed_count));
+    } else {
+        Atomic::store(false, reinterpret_cast<jlong *>(&_success));
+    }
+}
 
+size_t HeapInspection::populate_table(KlassInfoTable* cit, BoolObjectClosure *filter, uint parallel_thread_num) {
+    // Try parallel first.
+    if (parallel_thread_num > 1) {
+        ResourceMark rm;
+        FlexibleWorkGang* gang = Universe::heap()->get_safepoint_workers();
+        if (gang != NULL) {
+            // The GC provided a WorkGang to be used during a safepoint.
+            // Can't run with more threads than provided by the WorkGang.
+            WithUpdatedActiveWorkers update_and_restore(gang, parallel_thread_num);
+            ParallelObjectIterator* poi = Universe::heap()->parallel_object_iterator(gang->active_workers());
+            if (poi != NULL) {
+                // The GC supports parallel object iteration.
+                ParHeapInspectTask task(poi, cit, filter);
+                // Run task with the active workers.
+                Universe::heap()->run_task(&task);
+                delete poi;
+                if (task.success()) {
+                    return task.missed_count();
+                }
+            }
+        }
+    }
+
+    ResourceMark rm;
+    // If no parallel iteration available, run serially.
   RecordInstanceClosure ric(cit, filter);
   Universe::heap()->object_iterate(&ric);
   return ric.missed_count();
 }
 
-void HeapInspection::heap_inspection(outputStream* st) {
+void HeapInspection::heap_inspection(outputStream* st, uint parallel_thread_num) {
   ResourceMark rm;
-
   if (_print_help) {
     for (int c=0; c<KlassSizeStats::_num_columns; c++) {
       st->print("%s:\n\t", name_table[c]);
@@ -514,9 +600,9 @@ void HeapInspection::heap_inspection(outputStream* st) {
 
   KlassInfoTable cit(_print_class_stats);
   if (!cit.allocation_failed()) {
-    size_t missed_count = populate_table(&cit);
+    uintx missed_count = populate_table(&cit, NULL, parallel_thread_num);
     if (missed_count != 0) {
-      st->print_cr("WARNING: Ran out of C-heap; undercounted " SIZE_FORMAT
+      st->print_cr("WARNING: Ran out of C-heap; undercounted " UINTX_FORMAT
                    " total instances in data below",
                    missed_count);
     }
diff --git a/hotspot/src/share/vm/memory/heapInspection.hpp b/hotspot/src/share/vm/memory/heapInspection.hpp
index c5fec15c..d2fed80b 100644
--- a/hotspot/src/share/vm/memory/heapInspection.hpp
+++ b/hotspot/src/share/vm/memory/heapInspection.hpp
@@ -25,11 +25,14 @@
 #ifndef SHARE_VM_MEMORY_HEAPINSPECTION_HPP
 #define SHARE_VM_MEMORY_HEAPINSPECTION_HPP
 
+#include "utilities/workgroup.hpp"
 #include "memory/allocation.inline.hpp"
 #include "oops/oop.inline.hpp"
 #include "oops/annotations.hpp"
 #include "utilities/macros.hpp"
 
+class ParallelObjectIterator;
+
 #if INCLUDE_SERVICES
 
 
@@ -254,7 +257,8 @@ class KlassInfoTable: public StackObj {
   void iterate(KlassInfoClosure* cic);
   bool allocation_failed() { return _buckets == NULL; }
   size_t size_of_instances_in_words() const;
-
+  bool merge(KlassInfoTable* table);
+  bool merge_entry(const KlassInfoEntry* cie);
   friend class KlassInfoHisto;
 };
 
@@ -366,11 +370,47 @@ class HeapInspection : public StackObj {
                  bool print_class_stats, const char *columns) :
       _csv_format(csv_format), _print_help(print_help),
       _print_class_stats(print_class_stats), _columns(columns) {}
-  void heap_inspection(outputStream* st) NOT_SERVICES_RETURN;
-  size_t populate_table(KlassInfoTable* cit, BoolObjectClosure* filter = NULL) NOT_SERVICES_RETURN_(0);
+  void heap_inspection(outputStream* st, uint parallel_thread_num = 1) NOT_SERVICES_RETURN;
+  size_t populate_table(KlassInfoTable* cit, BoolObjectClosure* filter = NULL, uint parallel_thread_num = 1) NOT_SERVICES_RETURN_(0);
   static void find_instances_at_safepoint(Klass* k, GrowableArray<oop>* result) NOT_SERVICES_RETURN;
  private:
   void iterate_over_heap(KlassInfoTable* cit, BoolObjectClosure* filter = NULL);
 };
 
+// Parallel heap inspection task. Parallel inspection can fail due to
+// a native OOM when allocating memory for TL-KlassInfoTable.
+// _success will be set false on an OOM, and serial inspection tried.
+class ParHeapInspectTask : public AbstractGangTask {
+private:
+    ParallelObjectIterator *_poi;
+    KlassInfoTable *_shared_cit;
+    BoolObjectClosure *_filter;
+    uintx _missed_count;
+    bool _success;
+    Mutex _mutex;
+
+public:
+    ParHeapInspectTask(ParallelObjectIterator *poi,
+                       KlassInfoTable *shared_cit,
+                       BoolObjectClosure *filter) :
+            AbstractGangTask("Iterating heap"),
+            _poi(poi),
+            _shared_cit(shared_cit),
+            _filter(filter),
+            _missed_count(0),
+            _success(true),
+            _mutex(Mutex::leaf, "Parallel heap iteration data merge lock") {}
+
+    uintx missed_count() const {
+        return _missed_count;
+    }
+
+    bool success() {
+        return _success;
+    }
+
+    virtual void work(uint worker_id);
+};
+
+
 #endif // SHARE_VM_MEMORY_HEAPINSPECTION_HPP
diff --git a/hotspot/src/share/vm/runtime/arguments.hpp b/hotspot/src/share/vm/runtime/arguments.hpp
index 03f293e3..9dbe99ef 100644
--- a/hotspot/src/share/vm/runtime/arguments.hpp
+++ b/hotspot/src/share/vm/runtime/arguments.hpp
@@ -424,12 +424,6 @@ class Arguments : AllStatic {
   static ArgsRange check_memory_size(julong size, julong min_size);
   static ArgsRange parse_memory_size(const char* s, julong* long_arg,
                                      julong min_size);
-  // Parse a string for a unsigned integer.  Returns true if value
-  // is an unsigned integer greater than or equal to the minimum
-  // parameter passed and returns the value in uintx_arg.  Returns
-  // false otherwise, with uintx_arg undefined.
-  static bool parse_uintx(const char* value, uintx* uintx_arg,
-                          uintx min_size);
 
   // methods to build strings from individual args
   static void build_jvm_args(const char* arg);
@@ -478,6 +472,12 @@ class Arguments : AllStatic {
  public:
   // Parses the arguments, first phase
   static jint parse(const JavaVMInitArgs* args);
+  // Parse a string for a unsigned integer.  Returns true if value
+  // is an unsigned integer greater than or equal to the minimum
+  // parameter passed and returns the value in uintx_arg.  Returns
+  // false otherwise, with uintx_arg undefined
+  static bool parse_uintx(const char* value, uintx* uintx_arg,
+                            uintx min_size);
   // Apply ergonomics
   static jint apply_ergo();
   // Adjusts the arguments after the OS have adjusted the arguments
diff --git a/hotspot/src/share/vm/services/attachListener.cpp b/hotspot/src/share/vm/services/attachListener.cpp
index 0f51378d..d7529a44 100644
--- a/hotspot/src/share/vm/services/attachListener.cpp
+++ b/hotspot/src/share/vm/services/attachListener.cpp
@@ -214,9 +214,11 @@ jint dump_heap(AttachOperation* op, outputStream* out) {
 //
 // Input arguments :-
 //   arg0: "-live" or "-all"
+//   arg1: parallel thread number
 static jint heap_inspection(AttachOperation* op, outputStream* out) {
   bool live_objects_only = true;   // default is true to retain the behavior before this change is made
   const char* arg0 = op->arg(0);
+  uint parallel_thread_num = MAX2<uint>(1, (uint)os::initial_active_processor_count() * 3 / 8);
   if (arg0 != NULL && (strlen(arg0) > 0)) {
     if (strcmp(arg0, "-all") != 0 && strcmp(arg0, "-live") != 0) {
       out->print_cr("Invalid argument to inspectheap operation: %s", arg0);
@@ -224,7 +226,16 @@ static jint heap_inspection(AttachOperation* op, outputStream* out) {
     }
     live_objects_only = strcmp(arg0, "-live") == 0;
   }
-  VM_GC_HeapInspection heapop(out, live_objects_only /* request full gc */);
+  const char* num_str = op->arg(1);
+  if (num_str != NULL && num_str[0] != '\0') {
+      uintx num;
+      if (!Arguments::parse_uintx(num_str, &num, 0)) {
+          out->print_cr("Invalid parallel thread number: [%s]", num_str);
+          return JNI_ERR;
+      }
+      parallel_thread_num = num == 0 ? parallel_thread_num : (uint)num;
+  }
+  VM_GC_HeapInspection heapop(out, live_objects_only /* request full gc */, parallel_thread_num);
   VMThread::execute(&heapop);
   return JNI_OK;
 }
diff --git a/hotspot/src/share/vm/utilities/workgroup.hpp b/hotspot/src/share/vm/utilities/workgroup.hpp
index dd956515..7e0fc973 100644
--- a/hotspot/src/share/vm/utilities/workgroup.hpp
+++ b/hotspot/src/share/vm/utilities/workgroup.hpp
@@ -163,6 +163,7 @@ public:
   virtual uint active_workers() const {
     return _total_workers;
   }
+
   bool terminate() const {
     return _terminate;
   }
@@ -325,6 +326,10 @@ class FlexibleWorkGang: public WorkGang {
     _active_workers(UseDynamicNumberOfGCThreads ? 1U : ParallelGCThreads) {}
   // Accessors for fields
   virtual uint active_workers() const { return _active_workers; }
+  uint update_active_workers(uint v) {
+      _active_workers = MIN2(v, _active_workers);
+      return _active_workers;
+  }
   void set_active_workers(uint v) {
     assert(v <= _total_workers,
            "Trying to set more workers active than there are");
@@ -339,7 +344,21 @@ class FlexibleWorkGang: public WorkGang {
     return _started_workers < _active_workers;
   }
 };
-
+class WithUpdatedActiveWorkers : public StackObj {
+private:
+    FlexibleWorkGang* const _gang;
+    const uint              _old_active_workers;
+public:
+    WithUpdatedActiveWorkers(FlexibleWorkGang* gang, uint requested_num_workers) :
+            _gang(gang),
+            _old_active_workers(gang->active_workers()) {
+        uint capped_num_workers = MIN2(requested_num_workers, gang->active_workers());
+        gang->update_active_workers(capped_num_workers);
+    }
+    ~WithUpdatedActiveWorkers() {
+        _gang->set_active_workers(_old_active_workers);
+    }
+};
 // Work gangs in garbage collectors: 2009-06-10
 //
 // SharedHeap - work gang for stop-the-world parallel collection.
diff --git a/jdk/src/share/classes/sun/tools/jmap/JMap.java b/jdk/src/share/classes/sun/tools/jmap/JMap.java
index 5d349fc0..e891b6c5 100644
--- a/jdk/src/share/classes/sun/tools/jmap/JMap.java
+++ b/jdk/src/share/classes/sun/tools/jmap/JMap.java
@@ -47,7 +47,8 @@ public class JMap {
     private static String HISTO_OPTION = "-histo";
     private static String LIVE_HISTO_OPTION = "-histo:live";
     private static String DUMP_OPTION_PREFIX = "-dump:";
-
+    private static final String LIVE_OBJECTS_OPTION = "-live";
+    private static final String ALL_OBJECTS_OPTION = "-all";
     // These options imply the use of a SA tool
     private static String SA_TOOL_OPTIONS =
       "-heap|-heap:format=b|-clstats|-finalizerinfo";
@@ -134,10 +135,10 @@ public class JMap {
             // Here we handle the built-in options
             // As more options are added we should create an abstract tool class and
             // have a table to map the options
-            if (option.equals(HISTO_OPTION)) {
-                histo(pid, false);
-            } else if (option.equals(LIVE_HISTO_OPTION)) {
-                histo(pid, true);
+            if (option.equals("-histo")) {
+                histo(pid, "");
+            } else if (option.startsWith("-histo:")) {
+                histo(pid, option.substring("-histo:".length()));
             } else if (option.startsWith(DUMP_OPTION_PREFIX)) {
                 dump(pid, option);
             } else {
@@ -216,12 +217,26 @@ public class JMap {
         return null;
     }
 
-    private static final String LIVE_OBJECTS_OPTION = "-live";
-    private static final String ALL_OBJECTS_OPTION = "-all";
-    private static void histo(String pid, boolean live) throws IOException {
+
+    private static void histo(String pid, String options) throws IOException {
         VirtualMachine vm = attach(pid);
-        InputStream in = ((HotSpotVirtualMachine)vm).
-            heapHisto(live ? LIVE_OBJECTS_OPTION : ALL_OBJECTS_OPTION);
+        String parallel = null;
+        String liveopt = "-all";
+        if (options.startsWith("live")) {
+            liveopt = "-live";
+        }
+        String[] subopts = options.split(",");
+        for (int i = 0; i < subopts.length; i++) {
+            String subopt = subopts[i];
+            if (subopt.startsWith("parallel=")) {
+                parallel = subopt.substring("parallel=".length());
+                if (parallel == null) {
+                    System.err.println("Fail: no number provided in option: '" + subopt + "'");
+                    System.exit(1);
+                }
+            }
+        }
+        InputStream in = ((HotSpotVirtualMachine)vm).heapHisto(liveopt,parallel);
         drain(vm, in);
     }
 
@@ -360,6 +375,10 @@ public class JMap {
             System.err.println("    -heap                to print java heap summary");
             System.err.println("    -histo[:live]        to print histogram of java object heap; if the \"live\"");
             System.err.println("                         suboption is specified, only count live objects");
+            System.err.println("    parallel=<number>  parallel threads number for heap iteration:");
+            System.err.println("                         parallel=0 default behavior, use predefined number of threads");
+            System.err.println("                         parallel=1 disable parallel heap iteration");
+            System.err.println("                         parallel=<N> use N threads for parallel heap iteration");
             System.err.println("    -clstats             to print class loader statistics");
             System.err.println("    -finalizerinfo       to print information on objects awaiting finalization");
             System.err.println("    -dump:<dump-options> to dump java heap in hprof binary format");
diff --git a/jdk/test/sun/tools/common/ApplicationSetup.sh b/jdk/test/sun/tools/common/ApplicationSetup.sh
index 64da8b96..c0f6a636 100644
--- a/jdk/test/sun/tools/common/ApplicationSetup.sh
+++ b/jdk/test/sun/tools/common/ApplicationSetup.sh
@@ -42,8 +42,15 @@
 startApplication()
 {
   appOutput="${TESTCLASSES}/Application.out"
-
-  ${JAVA} -XX:+UsePerfData -classpath "${TESTCLASSPATH:-${TESTCLASSES}}" "$@" > "$appOutput" 2>&1 &
+  if [ $# -gt 2 ]; then
+    if [ $3 = "defineGC" ]; then
+      ${JAVA} -XX:+UsePerfData -XX:+$4 -classpath "${TESTCLASSPATH:-${TESTCLASSES}}" "$@" > "$appOutput" 2>&1 &
+    else
+      ${JAVA} -XX:+UsePerfData -classpath "${TESTCLASSPATH:-${TESTCLASSES}}" "$@" > "$appOutput" 2>&1 &
+    fi
+  else
+    ${JAVA} -XX:+UsePerfData -classpath "${TESTCLASSPATH:-${TESTCLASSES}}" "$@" > "$appOutput" 2>&1 &
+  fi
   appJavaPid="$!"
   appOtherPid=
   appPidList="$appJavaPid"
@@ -120,7 +127,6 @@ startApplication()
   echo "INFO: $1 output is in $appOutput"
 }
 
-
 # Stops a simple application by invoking ShutdownSimpleApplication
 # class with a specific port-file, usage:
 #   stopApplication port-file
diff --git a/jdk/test/sun/tools/jmap/ParallelInspection.sh b/jdk/test/sun/tools/jmap/ParallelInspection.sh
new file mode 100644
index 00000000..69e51a76
--- /dev/null
+++ b/jdk/test/sun/tools/jmap/ParallelInspection.sh
@@ -0,0 +1,79 @@
+#!/bin/sh
+
+#
+# Copyright (c) Huawei Technologies Co., Ltd. 2020. All rights reserved.
+#
+
+# @test
+# @summary Unit test for jmap parallel heap inspection feature
+# @library ../common
+# @build SimpleApplication ShutdownSimpleApplication
+# @run shell ParallelInspection.sh
+
+. ${TESTSRC}/../common/CommonSetup.sh
+. ${TESTSRC}/../common/ApplicationSetup.sh
+# parallel num in G1GC
+# Start application and use PORTFILE for coordination
+PORTFILE="${TESTCLASSES}"/shutdown.port
+startApplication SimpleApplication "${PORTFILE}" defineGC UseG1GC
+
+# all return statuses are checked in this test
+set +e
+
+failed=0
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=0 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=1 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=2 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=0 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=1 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=2 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+set -e
+
+stopApplication "${PORTFILE}"
+waitForApplication
+
+# parallel num in ParallelGC
+# Start application and use PORTFILE for coordination
+PORTFILE="${TESTCLASSES}"/shutdown.port
+startApplication SimpleApplication "${PORTFILE}" defineGC UseParallelGC
+
+# all return statuses are checked in this test
+set +e
+
+failed=0
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=0 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=1 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:parallel=2 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=0 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=1 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+
+${JMAP} -J-XX:+UsePerfData -histo:live,parallel=2 $appJavaPid
+if [ $? != 0 ]; then failed=1; fi
+set -e
+
+stopApplication "${PORTFILE}"
+waitForApplication
+
+exit $failed
-- 
2.19.0