g1InCSetState.hpp revision 9056:dc9930a04ab0 
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24
25#ifndef SHARE_VM_GC_G1_G1INCSETSTATE_HPP
26#define SHARE_VM_GC_G1_G1INCSETSTATE_HPP
27
28#include "gc/g1/g1BiasedArray.hpp"
29#include "gc/g1/heapRegion.hpp"
30#include "memory/allocation.hpp"
31
32// Per-region state during garbage collection.
33struct InCSetState {
34 public:
35  // We use different types to represent the state value. Particularly SPARC puts
36  // values in structs from "left to right", i.e. MSB to LSB. This results in many
37  // unnecessary shift operations when loading and storing values of this type.
38  // This degrades performance significantly (>10%) on that platform.
39  // Other tested ABIs do not seem to have this problem, and actually tend to
40  // favor smaller types, so we use the smallest usable type there.
41#ifdef SPARC
42  #define CSETSTATE_FORMAT INTPTR_FORMAT
43  typedef intptr_t in_cset_state_t;
44#else
45  #define CSETSTATE_FORMAT "%d"
46  typedef int8_t in_cset_state_t;
47#endif
48 private:
49  in_cset_state_t _value;
50 public:
51  enum {
52    // Selection of the values were driven to micro-optimize the encoding and
53    // frequency of the checks.
54    // The most common check is whether the region is in the collection set or not.
55    // This encoding allows us to use an != 0 check which in some architectures
56    // (x86*) can be encoded slightly more efficently than a normal comparison
57    // against zero.
58    // The same situation occurs when checking whether the region is humongous
59    // or not, which is encoded by values < 0.
60    // The other values are simply encoded in increasing generation order, which
61    // makes getting the next generation fast by a simple increment.
62    Humongous    = -1,    // The region is humongous - note that actually any value < 0 would be possible here.
63    NotInCSet    =  0,    // The region is not in the collection set.
64    Young        =  1,    // The region is in the collection set and a young region.
65    Old          =  2,    // The region is in the collection set and an old region.
66    Num
67  };
68
69  InCSetState(in_cset_state_t value = NotInCSet) : _value(value) {
70    assert(is_valid(), "Invalid state %d", _value);
71  }
72
73  in_cset_state_t value() const        { return _value; }
74
75  void set_old()                       { _value = Old; }
76
77  bool is_in_cset_or_humongous() const { return _value != NotInCSet; }
78  bool is_in_cset() const              { return _value > NotInCSet; }
79  bool is_humongous() const            { return _value < NotInCSet; }
80  bool is_young() const                { return _value == Young; }
81  bool is_old() const                  { return _value == Old; }
82
83#ifdef ASSERT
84  bool is_default() const              { return !is_in_cset_or_humongous(); }
85  bool is_valid() const                { return (_value >= Humongous) && (_value < Num); }
86  bool is_valid_gen() const            { return (_value >= Young && _value <= Old); }
87#endif
88};
89
90// Instances of this class are used for quick tests on whether a reference points
91// into the collection set and into which generation or is a humongous object
92//
93// Each of the array's elements indicates whether the corresponding region is in
94// the collection set and if so in which generation, or a humongous region.
95//
96// We use this to speed up reference processing during young collection and
97// quickly reclaim humongous objects. For the latter, by making a humongous region
98// succeed this test, we sort-of add it to the collection set. During the reference
99// iteration closures, when we see a humongous region, we then simply mark it as
100// referenced, i.e. live.
101class G1InCSetStateFastTestBiasedMappedArray : public G1BiasedMappedArray<InCSetState> {
102 protected:
103  InCSetState default_value() const { return InCSetState::NotInCSet; }
104 public:
105  void set_humongous(uintptr_t index) {
106    assert(get_by_index(index).is_default(),
107           "State at index " INTPTR_FORMAT " should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value());
108    set_by_index(index, InCSetState::Humongous);
109  }
110
111  void clear_humongous(uintptr_t index) {
112    set_by_index(index, InCSetState::NotInCSet);
113  }
114
115  void set_in_young(uintptr_t index) {
116    assert(get_by_index(index).is_default(),
117           "State at index " INTPTR_FORMAT " should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value());
118    set_by_index(index, InCSetState::Young);
119  }
120
121  void set_in_old(uintptr_t index) {
122    assert(get_by_index(index).is_default(),
123           "State at index " INTPTR_FORMAT " should be default but is " CSETSTATE_FORMAT, index, get_by_index(index).value());
124    set_by_index(index, InCSetState::Old);
125  }
126
127  bool is_in_cset_or_humongous(HeapWord* addr) const { return at(addr).is_in_cset_or_humongous(); }
128  bool is_in_cset(HeapWord* addr) const { return at(addr).is_in_cset(); }
129  bool is_in_cset(const HeapRegion* hr) const { return get_by_index(hr->hrm_index()).is_in_cset(); }
130  InCSetState at(HeapWord* addr) const { return get_by_address(addr); }
131  void clear() { G1BiasedMappedArray<InCSetState>::clear(); }
132  void clear(const HeapRegion* hr) { return set_by_index(hr->hrm_index(), InCSetState::NotInCSet); }
133};
134
135#endif // SHARE_VM_GC_G1_G1INCSETSTATE_HPP
136