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