first pass at cache

This commit is contained in:
Joe Thornber 2011-10-21 16:57:28 +01:00
parent ad8a70ce76
commit 97f8d913e2
4 changed files with 402 additions and 1 deletions

253
cache.h Normal file
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#ifndef CACHE_H
#define CACHE_H
#include <boost/intrusive/circular_list_algorithms.hpp>
#include <boost/intrusive/rbtree_algorithms.hpp>
#include <boost/optional.hpp>
#include <list>
#include <map>
#include <stdexcept>
//----------------------------------------------------------------
namespace base {
// FIXME: move somewhere more useful
template <typename T>
struct deleter {
void operator()(T *t) {
delete t;
}
};
// ValueTraits needs to define value_type, key_type and a get_key()
// static function. Commonly you will want value_type to be a
// shared_ptr, with any teardown specific stuff in the destructor.
template <typename ValueTraits>
class cache {
public:
typedef typename ValueTraits::value_type value_type;
typedef typename ValueTraits::key_type key_type;
cache(unsigned max_entries);
~cache();
void insert(value_type const &v);
boost::optional<value_type> get(key_type const &k);
void put(value_type const &k);
private:
void make_space();
struct value_entry {
// FIXME: this means the cached object must have a
// default constructor also, which is a shame.
// so we can construct the headers.
value_entry()
: ref_count_(0) {
}
explicit value_entry(value_type v)
: ref_count_(0),
v_(v) {
}
struct {
value_entry *next_, *prev_;
} lru_;
struct {
value_entry *parent_, *left_, *right_;
int color_;
} lookup_;
unsigned ref_count_;
value_type v_;
};
struct value_ptr_cmp {
bool operator() (value_entry const *lhs, value_entry const *rhs) {
key_type k1 = ValueTraits::get_key(lhs->v_);
key_type k2 = ValueTraits::get_key(rhs->v_);
return k1 < k2;
}
};
struct key_value_ptr_cmp {
bool operator() (key_type const &k1, value_entry const *rhs) {
key_type k2 = ValueTraits::get_key(rhs->v_);
return k1 < k2;
}
bool operator() (value_entry const *lhs, key_type const &k2) {
key_type k1 = ValueTraits::get_key(lhs->v_);
return k1 < k2;
}
};
struct list_node_traits {
typedef value_entry node;
typedef value_entry *node_ptr;
typedef const value_entry *const_node_ptr;
static node_ptr get_next(const_node_ptr n) {
return n->lru_.next_;
}
static void set_next(node_ptr n, node_ptr next) {
n->lru_.next_ = next;
}
static node_ptr get_previous(const_node_ptr n) {
return n->lru_.prev_;
}
static void set_previous(node_ptr n, node_ptr prev) {
n->lru_.prev_ = prev;
}
};
struct rbtree_node_traits {
typedef value_entry node;
typedef value_entry *node_ptr;
typedef const value_entry * const_node_ptr;
typedef int color;
static node_ptr get_parent(const_node_ptr n) {
return n->lookup_.parent_;
}
static void set_parent(node_ptr n, node_ptr parent) {
n->lookup_.parent_ = parent;
}
static node_ptr get_left(const_node_ptr n) {
return n->lookup_.left_;
}
static void set_left(node_ptr n, node_ptr left) {
n->lookup_.left_ = left;
}
static node_ptr get_right(const_node_ptr n) {
return n->lookup_.right_;
}
static void set_right(node_ptr n, node_ptr right) {
n->lookup_.right_ = right;
}
static int get_color(const_node_ptr n) {
return n->lookup_.color_;
}
static void set_color(node_ptr n, color c) {
n->lookup_.color_ = c;
}
static color red() {
return 0;
}
static color black() {
return 1;
}
};
typedef boost::intrusive::circular_list_algorithms<list_node_traits> lru_algo;
typedef boost::intrusive::rbtree_algorithms<rbtree_node_traits> lookup_algo;
unsigned max_entries_;
unsigned current_entries_;
value_entry lru_header_;
value_entry lookup_header_;
};
template <typename ValueTraits>
cache<ValueTraits>::cache(unsigned max_entries)
: max_entries_(max_entries),
current_entries_(0) {
lru_algo::init_header(&lru_header_);
lookup_algo::init_header(&lookup_header_);
}
template <typename ValueTraits>
cache<ValueTraits>::~cache() {
deleter<value_entry> d;
lookup_algo::clear_and_dispose(&lookup_header_, d);
}
template <typename ValueTraits>
void
cache<ValueTraits>::insert(value_type const &v) {
make_space();
value_entry *node = new value_entry(v);
try {
lru_algo::link_after(&lru_header_, node);
try {
value_ptr_cmp cmp;
lookup_algo::insert_equal(&lookup_header_, &lookup_header_, node, cmp);
current_entries_++;
} catch (...) {
lru_algo::unlink(node);
throw;
}
} catch (...) {
delete node;
throw;
}
}
template <typename ValueTraits>
boost::optional<typename ValueTraits::value_type>
cache<ValueTraits>::get(key_type const &k) {
key_value_ptr_cmp cmp;
value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
if (node == &lookup_header_)
return boost::optional<value_type>();
if (!node->ref_count_++)
lru_algo::unlink(node);
return boost::optional<value_type>(node->v_);
}
template <typename ValueTraits>
void
cache<ValueTraits>::put(value_type const &v) {
// FIXME: the lookup will go once we use a proper hook
key_value_ptr_cmp cmp;
key_type k = ValueTraits::get_key(v);
value_entry *node = lookup_algo::find(&lookup_header_, k, cmp);
if (node == &lookup_header_)
throw std::runtime_error("invalid put");
if (!--node->ref_count_)
lru_algo::link_after(&lru_header_, node);
}
template <typename ValueTraits>
void
cache<ValueTraits>::make_space() {
if (current_entries_ == max_entries_) {
value_entry *node = lru_header_.lru_.prev_;
if (node == &lru_header_)
throw std::runtime_error("cache full");
lru_algo::unlink(node);
lookup_algo::unlink(node);
delete node;
current_entries_--;
}
}
}
//----------------------------------------------------------------
#endif

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TEST_SOURCE=\
unit-tests/block_t.cc \
unit-tests/btree_t.cc \
unit-tests/cache_t.cc \
unit-tests/endian_t.cc \
unit-tests/space_map_t.cc \
unit-tests/space_map_disk_t.cc \
@ -19,6 +20,9 @@ unit-tests/block_t: unit-tests/block_t.o
unit-tests/btree_t: unit-tests/btree_t.o $(OBJECTS)
g++ $(CPPFLAGS) -o $@ $+ $(LIBS)
unit-tests/cache_t: unit-tests/cache_t.o $(OBJECTS)
g++ $(CPPFLAGS) -o $@ $+ $(LIBS)
unit-tests/space_map_t: unit-tests/space_map_t.o $(OBJECTS)
g++ $(CPPFLAGS) -o $@ $+ $(LIBS)

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unit-tests/cache_t.cc Normal file
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#include "cache.h"
#define BOOST_TEST_MODULE CacheTests
#include <boost/test/included/unit_test.hpp>
#include <boost/shared_ptr.hpp>
using namespace boost;
using namespace base;
using namespace std;
//----------------------------------------------------------------
namespace {
struct Thing {
Thing()
: key_(0),
desc_("default constructed") {
}
Thing(unsigned n)
: key_(n),
desc_("foo bar") {
}
unsigned key_;
string desc_;
};
struct ThingTraits {
typedef unsigned key_type;
typedef Thing value_type;
static key_type get_key(value_type const &t) {
return t.key_;
}
};
struct SharedThingTraits {
typedef unsigned key_type;
typedef shared_ptr<Thing> value_type;
static key_type get_key(value_type const &p) {
return p->key_;
}
};
}
//----------------------------------------------------------------
BOOST_AUTO_TEST_CASE(cache_creation)
{
cache<ThingTraits> c(16);
}
BOOST_AUTO_TEST_CASE(cache_caches)
{
unsigned const COUNT = 16;
cache<ThingTraits> c(COUNT);
for (unsigned i = 0; i < COUNT; i++)
c.insert(Thing(i));
for (unsigned i = 0; i < COUNT; i++)
BOOST_ASSERT(c.get(i));
}
BOOST_AUTO_TEST_CASE(cache_drops_elements)
{
unsigned const COUNT = 1024;
unsigned const CACHE_SIZE = 16;
cache<ThingTraits> c(CACHE_SIZE);
for (unsigned i = 0; i < COUNT; i++)
c.insert(Thing(i));
for (unsigned i = 0; i < COUNT - CACHE_SIZE; i++)
BOOST_ASSERT(!c.get(i));
for (unsigned i = COUNT - CACHE_SIZE; i < COUNT; i++)
BOOST_ASSERT(c.get(i));
}
BOOST_AUTO_TEST_CASE(held_entries_count_towards_the_cache_limit)
{
unsigned const CACHE_SIZE = 16;
cache<ThingTraits> c(CACHE_SIZE);
unsigned i;
for (i = 0; i < CACHE_SIZE; i++) {
c.insert(Thing(i));
c.get(i);
}
BOOST_CHECK_THROW(c.insert(Thing(i)), runtime_error);
}
BOOST_AUTO_TEST_CASE(put_works)
{
unsigned const CACHE_SIZE = 16;
cache<ThingTraits> c(CACHE_SIZE);
unsigned i;
for (i = 0; i < CACHE_SIZE; i++) {
c.insert(Thing(i));
c.get(i);
c.put(Thing(i));
}
// should succeed
c.insert(Thing(i));
}
BOOST_AUTO_TEST_CASE(multiple_gets_works)
{
unsigned const CACHE_SIZE = 16;
cache<ThingTraits> c(CACHE_SIZE);
unsigned i;
for (i = 0; i < CACHE_SIZE; i++) {
c.insert(Thing(i));
c.get(i);
c.get(i);
c.put(Thing(i));
}
BOOST_CHECK_THROW(c.insert(Thing(i)), runtime_error);
}
BOOST_AUTO_TEST_CASE(shared_ptr_cache_works)
{
unsigned const CACHE_SIZE = 16;
cache<SharedThingTraits> c(CACHE_SIZE);
for (unsigned i = 0; i < CACHE_SIZE; i++) {
c.insert(shared_ptr<Thing>(new Thing(i)));
optional<shared_ptr<Thing> > maybe_ptr = c.get(i);
BOOST_ASSERT(maybe_ptr);
BOOST_ASSERT((*maybe_ptr)->key_ == i);
}
}
//----------------------------------------------------------------