cpython/Modules/_sqlite/cache.c

313 lines
7.7 KiB
C

/* 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 */
static 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;
}
node->key = Py_NewRef(key);
node->data = Py_NewRef(data);
node->prev = NULL;
node->next = NULL;
return node;
}
static void
pysqlite_node_dealloc(pysqlite_Node *self)
{
PyTypeObject *tp = Py_TYPE(self);
Py_DECREF(self->key);
Py_DECREF(self->data);
tp->tp_free(self);
Py_DECREF(tp);
}
static 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;
}
self->factory = Py_NewRef(factory);
self->decref_factory = 1;
return 0;
}
static void
pysqlite_cache_dealloc(pysqlite_Cache *self)
{
PyTypeObject *tp = Py_TYPE(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);
tp->tp_free(self);
Py_DECREF(tp);
}
PyObject* pysqlite_cache_get(pysqlite_Cache* self, PyObject* key)
{
pysqlite_Node* node;
pysqlite_Node* ptr;
PyObject* data;
node = (pysqlite_Node*)PyDict_GetItemWithError(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 if (PyErr_Occurred()) {
return NULL;
}
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);
}
}
/* We cannot replace this by PyObject_CallOneArg() since
* PyObject_CallFunction() has a special case when using a
* single tuple as argument. */
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;
}
return Py_NewRef(node->data);
}
static 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 PyType_Slot node_slots[] = {
{Py_tp_dealloc, pysqlite_node_dealloc},
{Py_tp_new, PyType_GenericNew},
{0, NULL},
};
static PyType_Spec node_spec = {
.name = MODULE_NAME ".Node",
.basicsize = sizeof(pysqlite_Node),
.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.slots = node_slots,
};
PyTypeObject *pysqlite_NodeType = NULL;
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}
};
static PyType_Slot cache_slots[] = {
{Py_tp_dealloc, pysqlite_cache_dealloc},
{Py_tp_methods, cache_methods},
{Py_tp_new, PyType_GenericNew},
{Py_tp_init, pysqlite_cache_init},
{0, NULL},
};
static PyType_Spec cache_spec = {
.name = MODULE_NAME ".Cache",
.basicsize = sizeof(pysqlite_Cache),
.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
.slots = cache_slots,
};
PyTypeObject *pysqlite_CacheType = NULL;
int
pysqlite_cache_setup_types(PyObject *mod)
{
pysqlite_NodeType = (PyTypeObject *)PyType_FromModuleAndSpec(mod, &node_spec, NULL);
if (pysqlite_NodeType == NULL) {
return -1;
}
pysqlite_CacheType = (PyTypeObject *)PyType_FromModuleAndSpec(mod, &cache_spec, NULL);
if (pysqlite_CacheType == NULL) {
return -1;
}
return 0;
}