1 /* cache .c - a LRU cache
2 *
3 * Copyright (C) 2004-2010 Gerhard Häring <gh@ghaering.de>
4 *
5 * This file is part of pysqlite.
6 *
7 * This software is provided 'as-is', without any express or implied
8 * warranty. In no event will the authors be held liable for any damages
9 * arising from the use of this software.
10 *
11 * Permission is granted to anyone to use this software for any purpose,
12 * including commercial applications, and to alter it and redistribute it
13 * freely, subject to the following restrictions:
14 *
15 * 1. The origin of this software must not be misrepresented; you must not
16 * claim that you wrote the original software. If you use this software
17 * in a product, an acknowledgment in the product documentation would be
18 * appreciated but is not required.
19 * 2. Altered source versions must be plainly marked as such, and must not be
20 * misrepresented as being the original software.
21 * 3. This notice may not be removed or altered from any source distribution.
22 */
23
24 #include "cache.h"
25 #include <limits.h>
26
27 /* only used internally */
pysqlite_new_node(PyObject * key,PyObject * data)28 pysqlite_Node* pysqlite_new_node(PyObject* key, PyObject* data)
29 {
30 pysqlite_Node* node;
31
32 node = (pysqlite_Node*) (pysqlite_NodeType.tp_alloc(&pysqlite_NodeType, 0));
33 if (!node) {
34 return NULL;
35 }
36
37 Py_INCREF(key);
38 node->key = key;
39
40 Py_INCREF(data);
41 node->data = data;
42
43 node->prev = NULL;
44 node->next = NULL;
45
46 return node;
47 }
48
pysqlite_node_dealloc(pysqlite_Node * self)49 void pysqlite_node_dealloc(pysqlite_Node* self)
50 {
51 Py_DECREF(self->key);
52 Py_DECREF(self->data);
53
54 Py_TYPE(self)->tp_free((PyObject*)self);
55 }
56
pysqlite_cache_init(pysqlite_Cache * self,PyObject * args,PyObject * kwargs)57 int pysqlite_cache_init(pysqlite_Cache* self, PyObject* args, PyObject* kwargs)
58 {
59 PyObject* factory;
60 int size = 10;
61
62 self->factory = NULL;
63
64 if (!PyArg_ParseTuple(args, "O|i", &factory, &size)) {
65 return -1;
66 }
67
68 /* minimum cache size is 5 entries */
69 if (size < 5) {
70 size = 5;
71 }
72 self->size = size;
73 self->first = NULL;
74 self->last = NULL;
75
76 self->mapping = PyDict_New();
77 if (!self->mapping) {
78 return -1;
79 }
80
81 Py_INCREF(factory);
82 self->factory = factory;
83
84 self->decref_factory = 1;
85
86 return 0;
87 }
88
pysqlite_cache_dealloc(pysqlite_Cache * self)89 void pysqlite_cache_dealloc(pysqlite_Cache* self)
90 {
91 pysqlite_Node* node;
92 pysqlite_Node* delete_node;
93
94 if (!self->factory) {
95 /* constructor failed, just get out of here */
96 return;
97 }
98
99 /* iterate over all nodes and deallocate them */
100 node = self->first;
101 while (node) {
102 delete_node = node;
103 node = node->next;
104 Py_DECREF(delete_node);
105 }
106
107 if (self->decref_factory) {
108 Py_DECREF(self->factory);
109 }
110 Py_DECREF(self->mapping);
111
112 Py_TYPE(self)->tp_free((PyObject*)self);
113 }
114
pysqlite_cache_get(pysqlite_Cache * self,PyObject * args)115 PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args)
116 {
117 PyObject* key = args;
118 pysqlite_Node* node;
119 pysqlite_Node* ptr;
120 PyObject* data;
121
122 node = (pysqlite_Node*)PyDict_GetItemWithError(self->mapping, key);
123 if (node) {
124 /* an entry for this key already exists in the cache */
125
126 /* increase usage counter of the node found */
127 if (node->count < LONG_MAX) {
128 node->count++;
129 }
130
131 /* if necessary, reorder entries in the cache by swapping positions */
132 if (node->prev && node->count > node->prev->count) {
133 ptr = node->prev;
134
135 while (ptr->prev && node->count > ptr->prev->count) {
136 ptr = ptr->prev;
137 }
138
139 if (node->next) {
140 node->next->prev = node->prev;
141 } else {
142 self->last = node->prev;
143 }
144 if (node->prev) {
145 node->prev->next = node->next;
146 }
147 if (ptr->prev) {
148 ptr->prev->next = node;
149 } else {
150 self->first = node;
151 }
152
153 node->next = ptr;
154 node->prev = ptr->prev;
155 if (!node->prev) {
156 self->first = node;
157 }
158 ptr->prev = node;
159 }
160 }
161 else if (PyErr_Occurred()) {
162 return NULL;
163 }
164 else {
165 /* There is no entry for this key in the cache, yet. We'll insert a new
166 * entry in the cache, and make space if necessary by throwing the
167 * least used item out of the cache. */
168
169 if (PyDict_GET_SIZE(self->mapping) == self->size) {
170 if (self->last) {
171 node = self->last;
172
173 if (PyDict_DelItem(self->mapping, self->last->key) != 0) {
174 return NULL;
175 }
176
177 if (node->prev) {
178 node->prev->next = NULL;
179 }
180 self->last = node->prev;
181 node->prev = NULL;
182
183 Py_DECREF(node);
184 }
185 }
186
187 data = PyObject_CallFunction(self->factory, "O", key);
188
189 if (!data) {
190 return NULL;
191 }
192
193 node = pysqlite_new_node(key, data);
194 if (!node) {
195 return NULL;
196 }
197 node->prev = self->last;
198
199 Py_DECREF(data);
200
201 if (PyDict_SetItem(self->mapping, key, (PyObject*)node) != 0) {
202 Py_DECREF(node);
203 return NULL;
204 }
205
206 if (self->last) {
207 self->last->next = node;
208 } else {
209 self->first = node;
210 }
211 self->last = node;
212 }
213
214 Py_INCREF(node->data);
215 return node->data;
216 }
217
pysqlite_cache_display(pysqlite_Cache * self,PyObject * args)218 PyObject* pysqlite_cache_display(pysqlite_Cache* self, PyObject* args)
219 {
220 pysqlite_Node* ptr;
221 PyObject* prevkey;
222 PyObject* nextkey;
223 PyObject* display_str;
224
225 ptr = self->first;
226
227 while (ptr) {
228 if (ptr->prev) {
229 prevkey = ptr->prev->key;
230 } else {
231 prevkey = Py_None;
232 }
233
234 if (ptr->next) {
235 nextkey = ptr->next->key;
236 } else {
237 nextkey = Py_None;
238 }
239
240 display_str = PyUnicode_FromFormat("%S <- %S -> %S\n",
241 prevkey, ptr->key, nextkey);
242 if (!display_str) {
243 return NULL;
244 }
245 PyObject_Print(display_str, stdout, Py_PRINT_RAW);
246 Py_DECREF(display_str);
247
248 ptr = ptr->next;
249 }
250
251 Py_RETURN_NONE;
252 }
253
254 static PyMethodDef cache_methods[] = {
255 {"get", (PyCFunction)pysqlite_cache_get, METH_O,
256 PyDoc_STR("Gets an entry from the cache or calls the factory function to produce one.")},
257 {"display", (PyCFunction)pysqlite_cache_display, METH_NOARGS,
258 PyDoc_STR("For debugging only.")},
259 {NULL, NULL}
260 };
261
262 PyTypeObject pysqlite_NodeType = {
263 PyVarObject_HEAD_INIT(NULL, 0)
264 MODULE_NAME "Node", /* tp_name */
265 sizeof(pysqlite_Node), /* tp_basicsize */
266 0, /* tp_itemsize */
267 (destructor)pysqlite_node_dealloc, /* tp_dealloc */
268 0, /* tp_vectorcall_offset */
269 0, /* tp_getattr */
270 0, /* tp_setattr */
271 0, /* tp_as_async */
272 0, /* tp_repr */
273 0, /* tp_as_number */
274 0, /* tp_as_sequence */
275 0, /* tp_as_mapping */
276 0, /* tp_hash */
277 0, /* tp_call */
278 0, /* tp_str */
279 0, /* tp_getattro */
280 0, /* tp_setattro */
281 0, /* tp_as_buffer */
282 Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE, /* tp_flags */
283 0, /* tp_doc */
284 0, /* tp_traverse */
285 0, /* tp_clear */
286 0, /* tp_richcompare */
287 0, /* tp_weaklistoffset */
288 0, /* tp_iter */
289 0, /* tp_iternext */
290 0, /* tp_methods */
291 0, /* tp_members */
292 0, /* tp_getset */
293 0, /* tp_base */
294 0, /* tp_dict */
295 0, /* tp_descr_get */
296 0, /* tp_descr_set */
297 0, /* tp_dictoffset */
298 (initproc)0, /* tp_init */
299 0, /* tp_alloc */
300 0, /* tp_new */
301 0 /* tp_free */
302 };
303
304 PyTypeObject pysqlite_CacheType = {
305 PyVarObject_HEAD_INIT(NULL, 0)
306 MODULE_NAME ".Cache", /* tp_name */
307 sizeof(pysqlite_Cache), /* tp_basicsize */
308 0, /* tp_itemsize */
309 (destructor)pysqlite_cache_dealloc, /* tp_dealloc */
310 0, /* tp_vectorcall_offset */
311 0, /* tp_getattr */
312 0, /* tp_setattr */
313 0, /* tp_as_async */
314 0, /* tp_repr */
315 0, /* tp_as_number */
316 0, /* tp_as_sequence */
317 0, /* tp_as_mapping */
318 0, /* tp_hash */
319 0, /* tp_call */
320 0, /* tp_str */
321 0, /* tp_getattro */
322 0, /* tp_setattro */
323 0, /* tp_as_buffer */
324 Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE, /* tp_flags */
325 0, /* tp_doc */
326 0, /* tp_traverse */
327 0, /* tp_clear */
328 0, /* tp_richcompare */
329 0, /* tp_weaklistoffset */
330 0, /* tp_iter */
331 0, /* tp_iternext */
332 cache_methods, /* tp_methods */
333 0, /* tp_members */
334 0, /* tp_getset */
335 0, /* tp_base */
336 0, /* tp_dict */
337 0, /* tp_descr_get */
338 0, /* tp_descr_set */
339 0, /* tp_dictoffset */
340 (initproc)pysqlite_cache_init, /* tp_init */
341 0, /* tp_alloc */
342 0, /* tp_new */
343 0 /* tp_free */
344 };
345
pysqlite_cache_setup_types(void)346 extern int pysqlite_cache_setup_types(void)
347 {
348 int rc;
349
350 pysqlite_NodeType.tp_new = PyType_GenericNew;
351 pysqlite_CacheType.tp_new = PyType_GenericNew;
352
353 rc = PyType_Ready(&pysqlite_NodeType);
354 if (rc < 0) {
355 return rc;
356 }
357
358 rc = PyType_Ready(&pysqlite_CacheType);
359 return rc;
360 }
361