4965777: GC changes to support use of discovered field for pending references
Summary: If and when the reference handler thread is able to use the discovered field to link reference objects in its pending list, so will GC. In that case, GC will scan through this field once a reference object has been placed on the pending list, but not scan that field before that stage, as the field is used by the concurrent GC thread to link discovered objects. When ReferenceHandleR thread does not use the discovered field for the purpose of linking the elements in the pending list, as would be the case in older JDKs, the JVM will fall back to the old behaviour of using the next field for that purpose.
Reviewed-by: jcoomes, mchung, stefank
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#ifndef SHARE_VM_MEMORY_HEAPINSPECTION_HPP
#define SHARE_VM_MEMORY_HEAPINSPECTION_HPP
#include "memory/allocation.inline.hpp"
#include "oops/oop.inline.hpp"
#ifndef SERVICES_KERNEL
// HeapInspection
// KlassInfoTable is a bucket hash table that
// maps klassOops to extra information:
// instance count and instance word size.
//
// A KlassInfoBucket is the head of a link list
// of KlassInfoEntry's
//
// KlassInfoHisto is a growable array of pointers
// to KlassInfoEntry's and is used to sort
// the entries.
class KlassInfoEntry: public CHeapObj {
private:
KlassInfoEntry* _next;
klassOop _klass;
long _instance_count;
size_t _instance_words;
public:
KlassInfoEntry(klassOop k, KlassInfoEntry* next) :
_klass(k), _instance_count(0), _instance_words(0), _next(next)
{}
KlassInfoEntry* next() { return _next; }
bool is_equal(klassOop k) { return k == _klass; }
klassOop klass() { return _klass; }
long count() { return _instance_count; }
void set_count(long ct) { _instance_count = ct; }
size_t words() { return _instance_words; }
void set_words(size_t wds) { _instance_words = wds; }
int compare(KlassInfoEntry* e1, KlassInfoEntry* e2);
void print_on(outputStream* st) const;
};
class KlassInfoClosure: public StackObj {
public:
// Called for each KlassInfoEntry.
virtual void do_cinfo(KlassInfoEntry* cie) = 0;
};
class KlassInfoBucket: public CHeapObj {
private:
KlassInfoEntry* _list;
KlassInfoEntry* list() { return _list; }
void set_list(KlassInfoEntry* l) { _list = l; }
public:
KlassInfoEntry* lookup(const klassOop k);
void initialize() { _list = NULL; }
void empty();
void iterate(KlassInfoClosure* cic);
};
class KlassInfoTable: public StackObj {
private:
int _size;
// An aligned reference address (typically the least
// address in the perm gen) used for hashing klass
// objects.
HeapWord* _ref;
KlassInfoBucket* _buckets;
uint hash(klassOop p);
KlassInfoEntry* lookup(const klassOop k);
public:
// Table size
enum {
cit_size = 20011
};
KlassInfoTable(int size, HeapWord* ref);
~KlassInfoTable();
bool record_instance(const oop obj);
void iterate(KlassInfoClosure* cic);
bool allocation_failed() { return _buckets == NULL; }
};
class KlassInfoHisto : public StackObj {
private:
GrowableArray<KlassInfoEntry*>* _elements;
GrowableArray<KlassInfoEntry*>* elements() const { return _elements; }
const char* _title;
const char* title() const { return _title; }
static int sort_helper(KlassInfoEntry** e1, KlassInfoEntry** e2);
void print_elements(outputStream* st) const;
public:
enum {
histo_initial_size = 1000
};
KlassInfoHisto(const char* title,
int estimatedCount);
~KlassInfoHisto();
void add(KlassInfoEntry* cie);
void print_on(outputStream* st) const;
void sort();
};
#endif // SERVICES_KERNEL
class HeapInspection : public AllStatic {
public:
static void heap_inspection(outputStream* st, bool need_prologue) KERNEL_RETURN;
static void find_instances_at_safepoint(klassOop k, GrowableArray<oop>* result) KERNEL_RETURN;
};
#endif // SHARE_VM_MEMORY_HEAPINSPECTION_HPP