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| 1 // Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file |
| 2 // for details. All rights reserved. Use of this source code is governed by a |
| 3 // BSD-style license that can be found in the LICENSE file. |
| 4 |
| 5 #ifndef VM_WEAK_TABLE_H_ |
| 6 #define VM_WEAK_TABLE_H_ |
| 7 |
| 8 #include "vm/globals.h" |
| 9 |
| 10 #include "platform/assert.h" |
| 11 #include "vm/raw_object.h" |
| 12 |
| 13 namespace dart { |
| 14 |
| 15 class WeakTable { |
| 16 public: |
| 17 explicit WeakTable(intptr_t size) : used_(0), count_(0) { |
| 18 ASSERT(size >= 0); |
| 19 if (size < kMinSize) { |
| 20 size = kMinSize; |
| 21 } |
| 22 data_ = reinterpret_cast<intptr_t*>(calloc(size, kEntrySize * kWordSize)); |
| 23 size_ = size; |
| 24 } |
| 25 |
| 26 static WeakTable* NewFrom(WeakTable* original) { |
| 27 intptr_t cnt = original->count(); |
| 28 intptr_t sz = original->size(); |
| 29 intptr_t new_sz = sz; |
| 30 |
| 31 if (cnt <= (sz / 4)) { |
| 32 // Reduce the capacity. |
| 33 new_sz = sz / 2; |
| 34 } else if (cnt > (sz / 2)) { |
| 35 // Increase the capacity. |
| 36 new_sz = sz * 2; |
| 37 if (new_sz < sz) { |
| 38 FATAL("Reached impossible state of having more weak table entries" |
| 39 " than memory available for heap objects."); |
| 40 } |
| 41 } |
| 42 return new WeakTable(new_sz); |
| 43 } |
| 44 |
| 45 intptr_t size() const { return size_; } |
| 46 intptr_t used() const { return used_; } |
| 47 intptr_t count() const { return count_; } |
| 48 |
| 49 bool IsValidEntryAt(intptr_t i) const { |
| 50 ASSERT(((ValueAt(i) == 0) && |
| 51 ((ObjectAt(i) == NULL) || |
| 52 (data_[ObjectIndex(i)] == kDeletedEntry))) || |
| 53 ((ValueAt(i) != 0) && |
| 54 (ObjectAt(i) != NULL) && |
| 55 (data_[ObjectIndex(i)] != kDeletedEntry))); |
| 56 return (data_[ValueIndex(i)] != 0); |
| 57 } |
| 58 |
| 59 void InvalidateAt(intptr_t i) { |
| 60 ASSERT(IsValidEntryAt(i)); |
| 61 SetValueAt(i, 0); |
| 62 } |
| 63 |
| 64 RawObject* ObjectAt(intptr_t i) const { |
| 65 return reinterpret_cast<RawObject*>(data_[ObjectIndex(i)]); |
| 66 } |
| 67 |
| 68 intptr_t ValueAt(intptr_t i) const { |
| 69 return data_[ValueIndex(i)]; |
| 70 } |
| 71 |
| 72 WeakTable* SetValue(RawObject* key, intptr_t val); |
| 73 |
| 74 intptr_t GetValue(RawObject* key) const { |
| 75 intptr_t sz = size(); |
| 76 intptr_t idx = Hash(key) % sz; |
| 77 RawObject* obj = ObjectAt(idx); |
| 78 while (obj != NULL) { |
| 79 if (obj == key) { |
| 80 return ValueAt(idx); |
| 81 } |
| 82 idx = (idx + 1) % sz; |
| 83 obj = ObjectAt(idx); |
| 84 } |
| 85 ASSERT(ValueAt(idx) == 0); |
| 86 return 0; |
| 87 } |
| 88 |
| 89 private: |
| 90 enum { |
| 91 kObjectOffset = 0, |
| 92 kValueOffset, |
| 93 kEntrySize, |
| 94 }; |
| 95 |
| 96 static const intptr_t kDeletedEntry = 1; // Equivalent to a tagged NULL. |
| 97 static const intptr_t kMinSize = 8; |
| 98 |
| 99 static intptr_t LimitFor(intptr_t size) { |
| 100 // Maintain a maximum of 75% fill rate. |
| 101 return 3 * (size / 4); |
| 102 } |
| 103 intptr_t limit() const { return LimitFor(size()); } |
| 104 |
| 105 intptr_t index(intptr_t i) const { |
| 106 ASSERT(i >= 0); |
| 107 ASSERT(i < size()); |
| 108 return i * kEntrySize; |
| 109 } |
| 110 |
| 111 void set_used(intptr_t val) { |
| 112 ASSERT(val <= limit()); |
| 113 used_ = val; |
| 114 } |
| 115 |
| 116 void set_count(intptr_t val) { |
| 117 ASSERT(val <= limit()); |
| 118 ASSERT(val <= used()); |
| 119 count_ = val; |
| 120 } |
| 121 |
| 122 intptr_t ObjectIndex(intptr_t i) const { |
| 123 return index(i) + kObjectOffset; |
| 124 } |
| 125 |
| 126 intptr_t ValueIndex(intptr_t i) const { |
| 127 return index(i) + kValueOffset; |
| 128 } |
| 129 |
| 130 void SetObjectAt(intptr_t i, RawObject* key) { |
| 131 data_[ObjectIndex(i)] = reinterpret_cast<intptr_t>(key); |
| 132 } |
| 133 |
| 134 void SetValueAt(intptr_t i, intptr_t val) { |
| 135 // Setting a value of 0 is equivalent to invalidating the entry. |
| 136 if (val == 0) { |
| 137 data_[ObjectIndex(i)] = kDeletedEntry; |
| 138 set_count(count() - 1); |
| 139 } |
| 140 data_[ValueIndex(i)] = val; |
| 141 } |
| 142 |
| 143 WeakTable* Rehash(); |
| 144 |
| 145 static intptr_t Hash(RawObject* key) { |
| 146 return reinterpret_cast<intptr_t>(key) >> kObjectAlignmentLog2; |
| 147 } |
| 148 |
| 149 // data_ contains size_ tuples of key/value. |
| 150 intptr_t* data_; |
| 151 // size_ keeps the number of entries in data_. used_ maintains the number of |
| 152 // non-NULL entries and will trigger rehashing if needed. count_ stores the |
| 153 // number valid entries, and will determine the size_ after rehashing. |
| 154 intptr_t size_; |
| 155 intptr_t used_; |
| 156 intptr_t count_; |
| 157 |
| 158 DISALLOW_IMPLICIT_CONSTRUCTORS(WeakTable); |
| 159 }; |
| 160 |
| 161 } // namespace dart |
| 162 |
| 163 #endif // VM_WEAK_TABLE_H_ |
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