[176] | 1 | /* -*- C++ -*- */ |
---|
| 2 | |
---|
| 3 | #ifndef _AOFHEAP_H_ |
---|
| 4 | #define _AOFHEAP_H_ |
---|
| 5 | |
---|
| 6 | #include <new> // for placement new |
---|
| 7 | using namespace std; |
---|
| 8 | |
---|
| 9 | /* |
---|
| 10 | |
---|
| 11 | A very simple address-oriented first-fit heap |
---|
| 12 | with immediate coalescing. |
---|
| 13 | |
---|
| 14 | Because the heap is stored as a sorted doubly-linked list, |
---|
| 15 | it's potentially quite expensive: |
---|
| 16 | |
---|
| 17 | cost of a malloc = O(f) {# of non-contiguous freed objects} |
---|
| 18 | cost of a free = O(f) {# of non-contiguous freed objects} |
---|
| 19 | |
---|
| 20 | Worst-case performance could be improved by using a balanced O(log n) dictionary |
---|
| 21 | (like an RB-tree). Also, the free list is threaded through the objects themselves, |
---|
| 22 | something that can cause O(f) page faults; keeping the free list data structures |
---|
| 23 | separate from the data (and in a contiguous region of memory) would avoid this problem. |
---|
| 24 | |
---|
| 25 | */ |
---|
| 26 | |
---|
| 27 | // Freed objects of at least FreeThreshold size are freed to the super heap. |
---|
| 28 | |
---|
| 29 | template <class SuperHeap, int FreeThreshold> |
---|
| 30 | class AOFFHeap : public SuperHeap { |
---|
| 31 | public: |
---|
| 32 | |
---|
| 33 | AOFFHeap (void) |
---|
| 34 | { |
---|
| 35 | freeList.setSize (0); |
---|
| 36 | freeList.setNext (&freeList); |
---|
| 37 | freeList.setPrev (&freeList); |
---|
| 38 | } |
---|
| 39 | |
---|
| 40 | ~AOFFHeap (void) { |
---|
| 41 | return; // FIX ME FIX ME FIX ME!!! |
---|
| 42 | // Free everything on the free list. |
---|
| 43 | freedObject * ptr = freeList.getNext(); |
---|
| 44 | while (ptr != &freeList) { |
---|
| 45 | freedObject * prev = ptr; |
---|
| 46 | ptr = ptr->getNext(); |
---|
| 47 | SuperHeap::free (prev); |
---|
| 48 | } |
---|
| 49 | } |
---|
| 50 | |
---|
| 51 | void * malloc (size_t sz) { |
---|
| 52 | // printf ("aoffheap malloc sz = %d\n", sz); |
---|
| 53 | assert (isValid()); |
---|
| 54 | assert (sz >= sizeof(freedObject) - sizeof(allocatedObject)); |
---|
| 55 | // Find the first object in the free list that fits. |
---|
| 56 | freedObject * ptr = freeList.getNext(); |
---|
| 57 | while ((ptr != &freeList) && (ptr->getSize() < sz + sizeof(freedObject))) { |
---|
| 58 | ptr = ptr->getNext(); |
---|
| 59 | } |
---|
| 60 | // If there wasn't a big-enough object available on the free list, |
---|
| 61 | // make a new one. |
---|
| 62 | if (ptr == &freeList) { |
---|
| 63 | |
---|
| 64 | // printf ("AOFF super malloc(%d)\n", sz + sizeof(allocatedObject)); |
---|
| 65 | |
---|
| 66 | void * buf = SuperHeap::malloc (sz + sizeof(allocatedObject)); |
---|
| 67 | if (buf == NULL) { |
---|
| 68 | assert (isValid()); |
---|
| 69 | return NULL; |
---|
| 70 | } |
---|
| 71 | freedObject * newptr |
---|
| 72 | = new (buf) freedObject (sz, NULL, NULL); |
---|
| 73 | assert (size(newptr->getStart()) == sz); |
---|
| 74 | assert (isValid()); |
---|
| 75 | return (void *) newptr->getStart(); |
---|
| 76 | } else { |
---|
| 77 | assert (ptr->getSize() >= sz); |
---|
| 78 | // Remove it from the free list. |
---|
| 79 | freedObject * prev = ptr->getPrev(); |
---|
| 80 | freedObject * next = ptr->getNext(); |
---|
| 81 | assert (prev->isValid()); |
---|
| 82 | assert (next->isValid()); |
---|
| 83 | // If it's bigger than the request size, |
---|
| 84 | // splice it up. |
---|
| 85 | if (ptr->getSize() - sz >= sizeof(freedObject)) { |
---|
| 86 | // There's room for another object. |
---|
| 87 | // Splice it off. |
---|
| 88 | size_t oldSize = ptr->getSize(); |
---|
| 89 | ptr->setSize (sz); |
---|
| 90 | freedObject * splicedObj = new (ptr->getSuccessor()) |
---|
| 91 | freedObject (oldSize - sz - sizeof(freedObject), |
---|
| 92 | prev, |
---|
| 93 | next); |
---|
| 94 | prev->setNext (splicedObj); |
---|
| 95 | next->setPrev (splicedObj); |
---|
| 96 | assert (splicedObj->isValid()); |
---|
| 97 | assert (isValid()); |
---|
| 98 | assert (size(ptr->getStart()) == sz); |
---|
| 99 | return (void *) ptr->getStart(); |
---|
| 100 | } else { |
---|
| 101 | assert (0); |
---|
| 102 | abort(); |
---|
| 103 | // It's just right. |
---|
| 104 | // Just remove it. |
---|
| 105 | prev->setNext (next); |
---|
| 106 | next->setPrev (prev); |
---|
| 107 | assert (isValid()); |
---|
| 108 | assert (size(ptr->getStart()) == sz); |
---|
| 109 | return (void *) ptr->getStart(); |
---|
| 110 | } |
---|
| 111 | } |
---|
| 112 | } |
---|
| 113 | |
---|
| 114 | void free (void * p) { |
---|
| 115 | assert (isValid()); |
---|
| 116 | // Put the object back in sorted order (by address). |
---|
| 117 | freedObject * thisObject = (freedObject *) ((char *) p - sizeof(allocatedObject)); |
---|
| 118 | assert (thisObject->getStart() == p); |
---|
| 119 | freedObject * prev = &freeList; |
---|
| 120 | freedObject * next = freeList.getNext(); |
---|
| 121 | while ((next != &freeList) && ((char *) thisObject > (char *) next)) { |
---|
| 122 | prev = next; |
---|
| 123 | next = next->getNext(); |
---|
| 124 | } |
---|
| 125 | // Check if this object is already on the free list |
---|
| 126 | // (i.e., it was already deleted). |
---|
| 127 | if (thisObject == next) { |
---|
| 128 | // printf ("Bad call.\n"); |
---|
| 129 | // Ignore the bad programmer and just walk away... |
---|
| 130 | return; |
---|
| 131 | } |
---|
| 132 | // Now insert this object. |
---|
| 133 | prev->setNext (thisObject); |
---|
| 134 | next->setPrev (thisObject); |
---|
| 135 | thisObject = new (thisObject) freedObject (thisObject->getSize(), prev, next); |
---|
| 136 | // See if we can coalesce. |
---|
| 137 | if (prev->getSuccessor() == thisObject) { |
---|
| 138 | assert (prev != &freeList); |
---|
| 139 | coalesce (prev, thisObject); |
---|
| 140 | thisObject = prev; |
---|
| 141 | assert (thisObject->isValid()); |
---|
| 142 | assert (thisObject->getSize() > 0); |
---|
| 143 | // printf ("coalesced prev with this, new size = %d\n", thisObject->getSize()); |
---|
| 144 | } |
---|
| 145 | if (thisObject->getSuccessor() == next) { |
---|
| 146 | coalesce (thisObject, next); |
---|
| 147 | assert (thisObject->isValid()); |
---|
| 148 | //printf ("coalesced this with next, new size = %d\n", thisObject->getSize()); |
---|
| 149 | } |
---|
| 150 | // If this object is big enough, free it. |
---|
| 151 | if (thisObject->getSize() >= FreeThreshold) { |
---|
| 152 | // printf ("freed this (size = %d)\n", thisObject->getSize()); |
---|
| 153 | freedObject * prev = thisObject->getPrev(); |
---|
| 154 | freedObject * next = thisObject->getNext(); |
---|
| 155 | prev->setNext (next); |
---|
| 156 | next->setPrev (prev); |
---|
| 157 | assert (thisObject->isValid()); |
---|
| 158 | SuperHeap::free (thisObject); |
---|
| 159 | } |
---|
| 160 | assert (isValid()); |
---|
| 161 | } |
---|
| 162 | |
---|
| 163 | //protected: |
---|
| 164 | inline static size_t size (void * p) |
---|
| 165 | { |
---|
| 166 | allocatedObject * thisObject = (allocatedObject *) p - 1; |
---|
| 167 | assert (thisObject->isValid()); |
---|
| 168 | return thisObject->getSize(); |
---|
| 169 | } |
---|
| 170 | |
---|
| 171 | |
---|
| 172 | private: |
---|
| 173 | |
---|
| 174 | int isValid (void) { |
---|
| 175 | // March through the whole list and check for validity. |
---|
| 176 | freedObject * ptr = freeList.getNext(); |
---|
| 177 | while (ptr != &freeList) { |
---|
| 178 | freedObject * prev = ptr; |
---|
| 179 | assert (prev->getNext()->getPrev() == prev); |
---|
| 180 | assert (prev->isValid()); |
---|
| 181 | ptr = ptr->getNext(); |
---|
| 182 | } |
---|
| 183 | return 1; |
---|
| 184 | } |
---|
| 185 | |
---|
| 186 | class freedObject; |
---|
| 187 | |
---|
| 188 | inline void coalesce (freedObject * curr, freedObject * succ) { |
---|
| 189 | // printf ("Coalesce %d with %d\n", curr->getSize(), succ->getSize()); |
---|
| 190 | assert (curr->getSuccessor() == succ); |
---|
| 191 | assert (succ->getPrev() == curr); |
---|
| 192 | assert (curr->getNext() == succ); |
---|
| 193 | curr->setNext (succ->getNext()); |
---|
| 194 | succ->getNext()->setPrev(curr); |
---|
| 195 | curr->setSize (curr->getSize() + succ->getSize() + sizeof(allocatedObject)); |
---|
| 196 | assert (curr->isValid()); |
---|
| 197 | } |
---|
| 198 | inline static size_t align (int sz) { |
---|
| 199 | return (sz + (sizeof(double) - 1)) & ~(sizeof(double) - 1); |
---|
| 200 | } |
---|
| 201 | |
---|
| 202 | class allocatedObject { |
---|
| 203 | public: |
---|
| 204 | allocatedObject (void) |
---|
| 205 | { |
---|
| 206 | size = 0; |
---|
| 207 | #ifndef NDEBUG |
---|
| 208 | magic = 0xfacefade; |
---|
| 209 | #endif |
---|
| 210 | } |
---|
| 211 | int isValid (void) const { |
---|
| 212 | return (size >= 0) && (magic == 0xfacefade); |
---|
| 213 | } |
---|
| 214 | void setSize (size_t sz) { size = sz; assert (isValid()); } |
---|
| 215 | int getSize (void) const { assert (isValid()); return size; } |
---|
| 216 | |
---|
| 217 | // Return the start of the next object. |
---|
| 218 | allocatedObject * getSuccessor (void) const { |
---|
| 219 | assert (isValid()); |
---|
| 220 | return (allocatedObject *) ((char *) (this + 1) + size); |
---|
| 221 | } |
---|
| 222 | |
---|
| 223 | // Return the start of the actual object (beyond the header). |
---|
| 224 | char * getStart (void) const { |
---|
| 225 | assert (isValid()); |
---|
| 226 | return ((char *) (this + 1)); |
---|
| 227 | } |
---|
| 228 | private: |
---|
| 229 | int size; |
---|
| 230 | int magic; |
---|
| 231 | }; |
---|
| 232 | |
---|
| 233 | class freedObject : public allocatedObject { |
---|
| 234 | public: |
---|
| 235 | freedObject (void) |
---|
| 236 | : prev ((freedObject *) 0xdeadbeef), |
---|
| 237 | next ((freedObject *) 0xdeadbeef) |
---|
| 238 | {} |
---|
| 239 | freedObject (size_t sz, |
---|
| 240 | freedObject * p, |
---|
| 241 | freedObject * n) |
---|
| 242 | : prev (p), |
---|
| 243 | next (n) |
---|
| 244 | { |
---|
| 245 | allocatedObject::setSize (sz); |
---|
| 246 | } |
---|
| 247 | int isValid (void) const { |
---|
| 248 | return (allocatedObject::isValid()); |
---|
| 249 | } |
---|
| 250 | freedObject * getPrev (void) const { assert (isValid()); return prev; } |
---|
| 251 | freedObject * getNext (void) const { assert (isValid()); return next; } |
---|
| 252 | void setPrev (freedObject * p) { assert (isValid()); prev = p; } |
---|
| 253 | void setNext (freedObject * p) { assert (isValid()); next = p; } |
---|
| 254 | private: |
---|
| 255 | freedObject * prev; |
---|
| 256 | freedObject * next; |
---|
| 257 | }; |
---|
| 258 | |
---|
| 259 | |
---|
| 260 | freedObject freeList; |
---|
| 261 | double _dummy; // Just to make sure that the freeList node won't ever be coalesced! |
---|
| 262 | }; |
---|
| 263 | |
---|
| 264 | #endif |
---|