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358 lines
12 KiB
C
358 lines
12 KiB
C
/* cache .c - a LRU cache
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*
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* Copyright (C) 2004-2010 Gerhard Häring <gh@ghaering.de>
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*
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* This file is part of pysqlite.
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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*
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include "cache.h"
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#include <limits.h>
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/* only used internally */
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pysqlite_Node* pysqlite_new_node(PyObject* key, PyObject* data)
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{
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pysqlite_Node* node;
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node = (pysqlite_Node*) (pysqlite_NodeType.tp_alloc(&pysqlite_NodeType, 0));
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if (!node) {
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return NULL;
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}
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Py_INCREF(key);
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node->key = key;
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Py_INCREF(data);
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node->data = data;
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node->prev = NULL;
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node->next = NULL;
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return node;
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}
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void pysqlite_node_dealloc(pysqlite_Node* self)
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{
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Py_DECREF(self->key);
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Py_DECREF(self->data);
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Py_TYPE(self)->tp_free((PyObject*)self);
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}
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int pysqlite_cache_init(pysqlite_Cache* self, PyObject* args, PyObject* kwargs)
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{
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PyObject* factory;
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int size = 10;
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self->factory = NULL;
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if (!PyArg_ParseTuple(args, "O|i", &factory, &size)) {
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return -1;
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}
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/* minimum cache size is 5 entries */
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if (size < 5) {
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size = 5;
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}
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self->size = size;
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self->first = NULL;
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self->last = NULL;
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self->mapping = PyDict_New();
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if (!self->mapping) {
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return -1;
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}
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Py_INCREF(factory);
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self->factory = factory;
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self->decref_factory = 1;
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return 0;
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}
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void pysqlite_cache_dealloc(pysqlite_Cache* self)
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{
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pysqlite_Node* node;
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pysqlite_Node* delete_node;
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if (!self->factory) {
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/* constructor failed, just get out of here */
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return;
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}
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/* iterate over all nodes and deallocate them */
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node = self->first;
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while (node) {
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delete_node = node;
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node = node->next;
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Py_DECREF(delete_node);
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}
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if (self->decref_factory) {
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Py_DECREF(self->factory);
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}
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Py_DECREF(self->mapping);
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Py_TYPE(self)->tp_free((PyObject*)self);
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}
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PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* args)
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{
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PyObject* key = args;
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pysqlite_Node* node;
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pysqlite_Node* ptr;
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PyObject* data;
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node = (pysqlite_Node*)PyDict_GetItem(self->mapping, key);
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if (node) {
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/* an entry for this key already exists in the cache */
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/* increase usage counter of the node found */
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if (node->count < LONG_MAX) {
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node->count++;
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}
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/* if necessary, reorder entries in the cache by swapping positions */
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if (node->prev && node->count > node->prev->count) {
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ptr = node->prev;
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while (ptr->prev && node->count > ptr->prev->count) {
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ptr = ptr->prev;
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}
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if (node->next) {
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node->next->prev = node->prev;
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} else {
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self->last = node->prev;
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}
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if (node->prev) {
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node->prev->next = node->next;
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}
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if (ptr->prev) {
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ptr->prev->next = node;
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} else {
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self->first = node;
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}
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node->next = ptr;
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node->prev = ptr->prev;
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if (!node->prev) {
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self->first = node;
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}
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ptr->prev = node;
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}
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} else {
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/* There is no entry for this key in the cache, yet. We'll insert a new
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* entry in the cache, and make space if necessary by throwing the
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* least used item out of the cache. */
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if (PyDict_Size(self->mapping) == self->size) {
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if (self->last) {
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node = self->last;
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if (PyDict_DelItem(self->mapping, self->last->key) != 0) {
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return NULL;
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}
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if (node->prev) {
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node->prev->next = NULL;
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}
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self->last = node->prev;
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node->prev = NULL;
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Py_DECREF(node);
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}
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}
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data = PyObject_CallFunction(self->factory, "O", key);
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if (!data) {
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return NULL;
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}
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node = pysqlite_new_node(key, data);
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if (!node) {
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return NULL;
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}
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node->prev = self->last;
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Py_DECREF(data);
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if (PyDict_SetItem(self->mapping, key, (PyObject*)node) != 0) {
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Py_DECREF(node);
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return NULL;
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}
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if (self->last) {
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self->last->next = node;
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} else {
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self->first = node;
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}
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self->last = node;
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}
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Py_INCREF(node->data);
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return node->data;
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}
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PyObject* pysqlite_cache_display(pysqlite_Cache* self, PyObject* args)
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{
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pysqlite_Node* ptr;
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PyObject* prevkey;
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PyObject* nextkey;
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PyObject* display_str;
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ptr = self->first;
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while (ptr) {
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if (ptr->prev) {
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prevkey = ptr->prev->key;
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} else {
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prevkey = Py_None;
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}
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if (ptr->next) {
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nextkey = ptr->next->key;
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} else {
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nextkey = Py_None;
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}
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display_str = PyUnicode_FromFormat("%S <- %S -> %S\n",
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prevkey, ptr->key, nextkey);
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if (!display_str) {
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return NULL;
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}
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PyObject_Print(display_str, stdout, Py_PRINT_RAW);
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Py_DECREF(display_str);
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ptr = ptr->next;
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}
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Py_INCREF(Py_None);
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return Py_None;
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}
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static PyMethodDef cache_methods[] = {
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{"get", (PyCFunction)pysqlite_cache_get, METH_O,
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PyDoc_STR("Gets an entry from the cache or calls the factory function to produce one.")},
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{"display", (PyCFunction)pysqlite_cache_display, METH_NOARGS,
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PyDoc_STR("For debugging only.")},
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{NULL, NULL}
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};
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PyTypeObject pysqlite_NodeType = {
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PyVarObject_HEAD_INIT(NULL, 0)
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MODULE_NAME "Node", /* tp_name */
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sizeof(pysqlite_Node), /* tp_basicsize */
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0, /* tp_itemsize */
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(destructor)pysqlite_node_dealloc, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_reserved */
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0, /* tp_repr */
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0, /* tp_as_number */
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0, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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0, /* tp_call */
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0, /* tp_str */
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0, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE, /* tp_flags */
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0, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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0, /* tp_iter */
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0, /* tp_iternext */
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0, /* tp_methods */
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0, /* tp_members */
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0, /* tp_getset */
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0, /* tp_base */
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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0, /* tp_dictoffset */
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(initproc)0, /* tp_init */
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0, /* tp_alloc */
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0, /* tp_new */
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0 /* tp_free */
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};
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PyTypeObject pysqlite_CacheType = {
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PyVarObject_HEAD_INIT(NULL, 0)
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MODULE_NAME ".Cache", /* tp_name */
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sizeof(pysqlite_Cache), /* tp_basicsize */
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0, /* tp_itemsize */
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(destructor)pysqlite_cache_dealloc, /* tp_dealloc */
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0, /* tp_print */
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0, /* tp_getattr */
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0, /* tp_setattr */
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0, /* tp_reserved */
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0, /* tp_repr */
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0, /* tp_as_number */
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0, /* tp_as_sequence */
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0, /* tp_as_mapping */
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0, /* tp_hash */
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0, /* tp_call */
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0, /* tp_str */
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0, /* tp_getattro */
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0, /* tp_setattro */
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0, /* tp_as_buffer */
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Py_TPFLAGS_DEFAULT|Py_TPFLAGS_BASETYPE, /* tp_flags */
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0, /* tp_doc */
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0, /* tp_traverse */
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0, /* tp_clear */
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0, /* tp_richcompare */
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0, /* tp_weaklistoffset */
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0, /* tp_iter */
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0, /* tp_iternext */
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cache_methods, /* tp_methods */
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0, /* tp_members */
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0, /* tp_getset */
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0, /* tp_base */
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0, /* tp_dict */
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0, /* tp_descr_get */
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0, /* tp_descr_set */
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0, /* tp_dictoffset */
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(initproc)pysqlite_cache_init, /* tp_init */
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0, /* tp_alloc */
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0, /* tp_new */
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0 /* tp_free */
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};
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extern int pysqlite_cache_setup_types(void)
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{
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int rc;
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pysqlite_NodeType.tp_new = PyType_GenericNew;
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pysqlite_CacheType.tp_new = PyType_GenericNew;
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rc = PyType_Ready(&pysqlite_NodeType);
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if (rc < 0) {
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return rc;
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}
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rc = PyType_Ready(&pysqlite_CacheType);
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return rc;
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}
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