1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
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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.
  33 struct 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.
 101 class 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
--- EOF ---