1 // Copyright 2012 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_ZONE_H_ 6 #define V8_ZONE_H_ 7 8 #include <limits> 9 10 #include "src/base/accounting-allocator.h" 11 #include "src/base/hashmap.h" 12 #include "src/base/logging.h" 13 #include "src/globals.h" 14 #include "src/list.h" 15 #include "src/splay-tree.h" 16 17 namespace v8 { 18 namespace internal { 19 20 // Forward declarations. 21 class Segment; 22 23 24 // The Zone supports very fast allocation of small chunks of 25 // memory. The chunks cannot be deallocated individually, but instead 26 // the Zone supports deallocating all chunks in one fast 27 // operation. The Zone is used to hold temporary data structures like 28 // the abstract syntax tree, which is deallocated after compilation. 29 // 30 // Note: There is no need to initialize the Zone; the first time an 31 // allocation is attempted, a segment of memory will be requested 32 // through a call to malloc(). 33 // 34 // Note: The implementation is inherently not thread safe. Do not use 35 // from multi-threaded code. 36 class Zone final { 37 public: 38 explicit Zone(base::AccountingAllocator* allocator); 39 ~Zone(); 40 41 // Allocate 'size' bytes of memory in the Zone; expands the Zone by 42 // allocating new segments of memory on demand using malloc(). 43 void* New(size_t size); 44 45 template <typename T> 46 T* NewArray(size_t length) { 47 DCHECK_LT(length, std::numeric_limits<size_t>::max() / sizeof(T)); 48 return static_cast<T*>(New(length * sizeof(T))); 49 } 50 51 // Deletes all objects and free all memory allocated in the Zone. Keeps one 52 // small (size <= kMaximumKeptSegmentSize) segment around if it finds one. 53 void DeleteAll(); 54 55 // Deletes the last small segment kept around by DeleteAll(). You 56 // may no longer allocate in the Zone after a call to this method. 57 void DeleteKeptSegment(); 58 59 // Returns true if more memory has been allocated in zones than 60 // the limit allows. 61 bool excess_allocation() const { 62 return segment_bytes_allocated_ > kExcessLimit; 63 } 64 65 size_t allocation_size() const { return allocation_size_; } 66 67 base::AccountingAllocator* allocator() const { return allocator_; } 68 69 private: 70 // All pointers returned from New() have this alignment. In addition, if the 71 // object being allocated has a size that is divisible by 8 then its alignment 72 // will be 8. ASan requires 8-byte alignment. 73 #ifdef V8_USE_ADDRESS_SANITIZER 74 static const size_t kAlignment = 8; 75 STATIC_ASSERT(kPointerSize <= 8); 76 #else 77 static const size_t kAlignment = kPointerSize; 78 #endif 79 80 // Never allocate segments smaller than this size in bytes. 81 static const size_t kMinimumSegmentSize = 8 * KB; 82 83 // Never allocate segments larger than this size in bytes. 84 static const size_t kMaximumSegmentSize = 1 * MB; 85 86 // Never keep segments larger than this size in bytes around. 87 static const size_t kMaximumKeptSegmentSize = 64 * KB; 88 89 // Report zone excess when allocation exceeds this limit. 90 static const size_t kExcessLimit = 256 * MB; 91 92 // The number of bytes allocated in this zone so far. 93 size_t allocation_size_; 94 95 // The number of bytes allocated in segments. Note that this number 96 // includes memory allocated from the OS but not yet allocated from 97 // the zone. 98 size_t segment_bytes_allocated_; 99 100 // Expand the Zone to hold at least 'size' more bytes and allocate 101 // the bytes. Returns the address of the newly allocated chunk of 102 // memory in the Zone. Should only be called if there isn't enough 103 // room in the Zone already. 104 Address NewExpand(size_t size); 105 106 // Creates a new segment, sets it size, and pushes it to the front 107 // of the segment chain. Returns the new segment. 108 inline Segment* NewSegment(size_t size); 109 110 // Deletes the given segment. Does not touch the segment chain. 111 inline void DeleteSegment(Segment* segment, size_t size); 112 113 // The free region in the current (front) segment is represented as 114 // the half-open interval [position, limit). The 'position' variable 115 // is guaranteed to be aligned as dictated by kAlignment. 116 Address position_; 117 Address limit_; 118 119 base::AccountingAllocator* allocator_; 120 121 Segment* segment_head_; 122 }; 123 124 125 // ZoneObject is an abstraction that helps define classes of objects 126 // allocated in the Zone. Use it as a base class; see ast.h. 127 class ZoneObject { 128 public: 129 // Allocate a new ZoneObject of 'size' bytes in the Zone. 130 void* operator new(size_t size, Zone* zone) { return zone->New(size); } 131 132 // Ideally, the delete operator should be private instead of 133 // public, but unfortunately the compiler sometimes synthesizes 134 // (unused) destructors for classes derived from ZoneObject, which 135 // require the operator to be visible. MSVC requires the delete 136 // operator to be public. 137 138 // ZoneObjects should never be deleted individually; use 139 // Zone::DeleteAll() to delete all zone objects in one go. 140 void operator delete(void*, size_t) { UNREACHABLE(); } 141 void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); } 142 }; 143 144 145 // The ZoneScope is used to automatically call DeleteAll() on a 146 // Zone when the ZoneScope is destroyed (i.e. goes out of scope) 147 class ZoneScope final { 148 public: 149 explicit ZoneScope(Zone* zone) : zone_(zone) { } 150 ~ZoneScope() { zone_->DeleteAll(); } 151 152 Zone* zone() const { return zone_; } 153 154 private: 155 Zone* zone_; 156 }; 157 158 159 // The ZoneAllocationPolicy is used to specialize generic data 160 // structures to allocate themselves and their elements in the Zone. 161 class ZoneAllocationPolicy final { 162 public: 163 explicit ZoneAllocationPolicy(Zone* zone) : zone_(zone) { } 164 void* New(size_t size) { return zone()->New(size); } 165 static void Delete(void* pointer) {} 166 Zone* zone() const { return zone_; } 167 168 private: 169 Zone* zone_; 170 }; 171 172 173 // ZoneLists are growable lists with constant-time access to the 174 // elements. The list itself and all its elements are allocated in the 175 // Zone. ZoneLists cannot be deleted individually; you can delete all 176 // objects in the Zone by calling Zone::DeleteAll(). 177 template <typename T> 178 class ZoneList final : public List<T, ZoneAllocationPolicy> { 179 public: 180 // Construct a new ZoneList with the given capacity; the length is 181 // always zero. The capacity must be non-negative. 182 ZoneList(int capacity, Zone* zone) 183 : List<T, ZoneAllocationPolicy>(capacity, ZoneAllocationPolicy(zone)) { } 184 185 void* operator new(size_t size, Zone* zone) { return zone->New(size); } 186 187 // Construct a new ZoneList by copying the elements of the given ZoneList. 188 ZoneList(const ZoneList<T>& other, Zone* zone) 189 : List<T, ZoneAllocationPolicy>(other.length(), 190 ZoneAllocationPolicy(zone)) { 191 AddAll(other, zone); 192 } 193 194 // We add some convenience wrappers so that we can pass in a Zone 195 // instead of a (less convenient) ZoneAllocationPolicy. 196 void Add(const T& element, Zone* zone) { 197 List<T, ZoneAllocationPolicy>::Add(element, ZoneAllocationPolicy(zone)); 198 } 199 void AddAll(const List<T, ZoneAllocationPolicy>& other, Zone* zone) { 200 List<T, ZoneAllocationPolicy>::AddAll(other, ZoneAllocationPolicy(zone)); 201 } 202 void AddAll(const Vector<T>& other, Zone* zone) { 203 List<T, ZoneAllocationPolicy>::AddAll(other, ZoneAllocationPolicy(zone)); 204 } 205 void InsertAt(int index, const T& element, Zone* zone) { 206 List<T, ZoneAllocationPolicy>::InsertAt(index, element, 207 ZoneAllocationPolicy(zone)); 208 } 209 Vector<T> AddBlock(T value, int count, Zone* zone) { 210 return List<T, ZoneAllocationPolicy>::AddBlock(value, count, 211 ZoneAllocationPolicy(zone)); 212 } 213 void Allocate(int length, Zone* zone) { 214 List<T, ZoneAllocationPolicy>::Allocate(length, ZoneAllocationPolicy(zone)); 215 } 216 void Initialize(int capacity, Zone* zone) { 217 List<T, ZoneAllocationPolicy>::Initialize(capacity, 218 ZoneAllocationPolicy(zone)); 219 } 220 221 void operator delete(void* pointer) { UNREACHABLE(); } 222 void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); } 223 }; 224 225 226 // A zone splay tree. The config type parameter encapsulates the 227 // different configurations of a concrete splay tree (see splay-tree.h). 228 // The tree itself and all its elements are allocated in the Zone. 229 template <typename Config> 230 class ZoneSplayTree final : public SplayTree<Config, ZoneAllocationPolicy> { 231 public: 232 explicit ZoneSplayTree(Zone* zone) 233 : SplayTree<Config, ZoneAllocationPolicy>(ZoneAllocationPolicy(zone)) {} 234 ~ZoneSplayTree() { 235 // Reset the root to avoid unneeded iteration over all tree nodes 236 // in the destructor. For a zone-allocated tree, nodes will be 237 // freed by the Zone. 238 SplayTree<Config, ZoneAllocationPolicy>::ResetRoot(); 239 } 240 241 void* operator new(size_t size, Zone* zone) { return zone->New(size); } 242 243 void operator delete(void* pointer) { UNREACHABLE(); } 244 void operator delete(void* pointer, Zone* zone) { UNREACHABLE(); } 245 }; 246 247 typedef base::TemplateHashMapImpl<ZoneAllocationPolicy> ZoneHashMap; 248 249 } // namespace internal 250 } // namespace v8 251 252 #endif // V8_ZONE_H_ 253
